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Post-flashover fires for structural design

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One of the major difficulties in designing structures to resist fires is the selection of post-flashover design fires. This paper proposes modificatio...

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A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point).

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Flame over is a term used to describe what happens in a compartment (structure) fire when the layer of combustible gasses ignites. This causes a "liquid" fire that immediately precedes Flashover, or the simultaneous ignition of everything in the room. I am preparing for a Godly flashover!

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fire dynamics series: predicting hot gas layer temperature and smoke layer height in a room fire with natural and forced ventilation

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Fire Dynamics Series: Predicting Hot Gas Layer Temperature and Smoke Layer Height in a Room Fire with Natural and Forced Ventilation - a PDH Online Course for Engineers, Surveyors and Architects

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PDHonline.com provides online (web-based) professional development courses (PDH hours units credits PDHs) continuing education units (CEU CEUs) and learning units (LU LUs) for engineer (engineers PE P.E.) land surveyor (surveyors LS PLS) and architect (architects AIA A.I.A. RA)

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'You have a legal obligation'
Smoke ventilation systems are life-saving and property and contents preserving but only if they are in full working order. Therefore, it is essential that a comprehensively tailored maintenance plan is put in place.
Under the terms of The Regulatory Reform (Fire Safety) Order 2005, the person responsible for the building has the legal obligation to ensure that premises and any facilities, equipment and devices are subject to a suitable system of maintenance and are maintained in an efficient state, in efficient working order, and in good repair. BS 9999:2008 states that it is essential that the fire protection measures can carry out their function in a fire. These should be checked periodically with all fire safety equipment maintained and tested in accordance with the relevant standard.

The legislation applies to virtually all premises and covers nearly every type of building, structure and open space.

At Smoke and Fire Ventilation Systems Limited we provide a range of services to ensure compliance and can offer the following:

Highly competitive, fully managed preventative maintenance regime to suit your specific smoke control requirements. This includes all manufacturers' equipment.

Our directly employed, experienced engineers who specialize in smoke vent systems.

6-month inspection service if required.

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Test certificate will be issued for smoke control systems.

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Smoke ventilation systems are life-saving and property and contents preserving but only if they are in full working order. Therefore, it is essential that a comprehensively tailored maintenance plan is put in place.

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Modelling of fire events using the NIST Fire Dynamics Simulator (FDS), including fire development, compartment temperatures, device activation times and flammable vapour explosive limits

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The Rim Fire (see pictures) that recently ravaged Yosemite National Park was started by a hunter's illegal campfire, according to authorities.

To determine the cause of such a fire, investigators rely on a number of observations and techniques, from telltale signs of flames to satellite imagery and chemical tests.

To better understand the science, National Geographic spoke with Richard Meier, a fire investigator in Sarasota, Florida, with John A. Kennedy and Associates, which analyzes fires and explosions for insurance companies and trials. Meier is also a staff member at the National Association of Fire Investigators, and the organization's treasurer.

How does one become a fire investigator?

There's a lot of different ways. In my case I spent about 23 years in engineering, in the manufacturing industry, which is a good thing: I used to make things, so I know how they work. A lot of people start off as firefighters and then become investigators.

What kind of training is required?

I started training a few years before I came to Kennedy. I started attending seminars and webinars. The National Fire Protection Association maintains a list of subjects that investigators must know to be certified. These include fire chemistry, fire dynamics, documenting the scene, and so on.

How do you determine the cause of a fire?

Science had nothing to do with fire investigation up to the late 1970s and early '80s. Before that it was based on old wives' tales. But now we use the scientific method.

The first thing is to find out where the fire started, which is what we call the "origin." The "area of origin" can be a broad area, like a room in a house ... The "point of origin" is the smallest area you can identify, which can be as small as a thimble or as big as a room. In the case of a wildland fire, you're probably talking [about] an area of origin around a half acre to an acre, and a point of origin the size of a campsite or a campfire.

After you figure out the origin, you look for things that could have served as an ignition source: a campfire, a flare, hunting ammunition (rare but sometimes happens), or a curved bottle that's left in the sun and acts as a magnifying glass. You have to test each one, at least logically, and determine if it's a competent ignition source for the fuels that you have.

Fuels could be dried grass or pine needles, which take a lot of energy to get started. You can light a piece of paper with a match, but you can't light a two-by-four with a match.

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Hot Science: How Investigators Determine the Causes of Fires

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The Rim Fire (see pictures) that recently ravaged Yosemite National Park was started by a hunter's illegal campfire, according to authorities. To determine the cause of such a fire, investigators rely on a number of observations and techniques, from telltale signs of flames to satellite imagery and chemical tests.

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How do you determine the cause of a fire? The aftermath of a blaze is overwhelming for a lot of reasons: physical damage, emotional damage, and more, but trained experts need to sort through that to figure out whether or not a fire was started intentionally or unintentionally in order to avoid repeat offenses. Here are a few ways that experts can figure out how a fire began.

First, professionals need to locate the point of origin of a fire. When looking at wildfires, we know they start small and gradually get hotter and larger, moving in a V- or U-shaped pattern. They often move with the direction of the wind and travel faster when moving uphill. In order to find the starting point, investigators will start at the outskirts of this V- or U-shape and work inward.

Clues to figuring out where that origin is beginning with determining the most blackened parts of a tree. The side of a tree with the most damage is probably facing the starting point of the blaze. Fires burn blades of grass from the bottom up, so fallen tips of grass that is unburned will point in the direction of the original fire.

As fires gain momentum over time, they tend to burn higher. So any unscorched fallen limbs of trees will be very close to the starting point of a wild blaze. Once the investigators have narrowed down a 100 square foot section of burned area as the starting point, they bring out the fine-toothed combs. Experts actually get down on hands and knees to search for any physical clues, like accelerants, matches, cigarette butts, tire marks, or footprints.

However, physical evidence is not enough to claim arson. This is where the real detective work begins. Eyewitness interviews and investigating motive will eventually determine whether or not foul play was involved.

For all of your fire safety needs and to keep up-to-date with more information posts about the natures of fire, contact Rich Fire today!

Source: http://science.howstuffworks.com/wildfire-arson.htm

Tags: Determining the Fire's Point of Origin, Fire Cause & Origin, Fire investigation, How do fire investigators determine the cause of a blaze, How to Determine the Origin of a Fire

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how do fire investigators determine the cause of a blaze

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How do you determine the cause of a fire? The aftermath of a blaze is overwhelming for a lot of reasons: physical damage, emotional damage, and more, but trained experts need to sort through that to figure out whether or not a fire was started intentionally or unintentionally in order to avoid repeat offenses.

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There are four logical components to the literature review presented:

The first part of the review describes the work completed for establishing a degree of fire damage assessment for commonly encountered materials in structure fires.

The second part isolates the work conducted on identifying fire patterns and the characteristics associated with these trends within the damage.

The third part of the review focuses on the possible causal factors influencing the location and magnitude of damage.

The fourth part of the review focuses on the practice of using damage in fire investigation to assist in determining the area of fire origin.

Literature on establishing a degree of fire damage assessment

When a fire develops in an enclosure, the products of combustion ( e.g. heat, soot) begin to influence the materials within the compartment. Thus, the lining materials for the walls, ceiling and floor, as well as the various materials that make up the contents within the compartment, are damaged by this exposure to the products of combustion. The fire investigation community terms the resulting damage as fire effects, which are defined as "the observable or measurable changes in or on a material as a result of exposure to the fire" (NFPA ).

The degree to which materials are influenced by the developing fire will be a function of the material characteristics, temperature of the products of combustion and the duration of exposure (NFPA ). There are numerous factors that may influence how a material is affected by heat and exposure to incomplete combustion products ( e.g. smoke, aerosols). The loss of mass from a material is typically dependent on the material and the exposure to heating. A short list of material properties that may also influence the effects of a material exposed to a fire environment includes: moisture content, thermal conductivity, density, specific heat, critical heat flux, ignition and flame spread propensity and heat of gasification/vaporization (NFPA ).

The damage data used by fire investigators in origin determination starts with the ability of the investigator to observe varying damage along surfaces of contents, walls, ceiling, floor and structural members. The fire investigator's observations are simply assessing the varying DOFD. Identification of varying DOFD throughout the compartment serves as the basis for interpretation by the investigator. Fire investigation textbooks, guides and studies describe the use of lines or areas of demarcation in assessing damage. The areas of damage and boundaries of those areas are often referred to as areas and lines of demarcation. Areas of demarcation are locations along a surface that exhibit similar damage characteristics ( e.g. magnitude of damage, type of fire effect, color, texture) and are in close proximity to each other. Lines of demarcation are "the borders defining the differences in certain heat and smoke effects of the fire on various materials. They appear between the affected area and adjacent, less-affected areas" (NFPA ). Fire investigators are instructed to visually and measurably identify these areas and lines of demarcation.

Ideally, the investigator would be able to look at a material's surface and distinguish the varying DOFD across its surface and this examination would be consistent with the findings of other qualified investigators. However, fire investigators currently use their visual interpretation to give vague descriptions on the varying degrees of damage when reporting their findings. Many fire investigation reports, textbooks and standards inconsistently report degrees of damage, using a wide range of undefined modifiers, such as greater, lesser, heavy, light, minor, moderate, major, severe and large, in an attempt to distinguish between levels of damage that they observe and are trying to convey (DeHaan and Icove ; Lentini ; Madrzykowski and Fleischmann ; NFPA ; Shanley et al. ).

There are a total of 17 fire effects listed in NFPA () that serve as the base list of observations for fire investigators (Table ). There are hundreds of materials that can be found in residential occupancies, as such there are thousands of studies that would need to be reviewed and summarized here to identify the characteristics of the material properties and the impact that heat has on each material. The focus of this literature review is to identify the work that has been done specifically for forensic applications that have been conducted for identifying ways to observe and characterize varying degrees of fire damage through measurable or visible means. Wood and gypsum wallboard (drywall) were the only materials that had sufficient literature to review in this context.

Wood (Char)

Wood has been and remains a common material used for construction of structures and contents. Therefore, fire investigators within most fire scenes typically find charred material. As such, fire investigators have written about the use of visible and measurable observations related to varying damage to wood for as long as fire investigation has been in existence (Rethoret ). However, the visible and measurable observations used in identifying the varying degree of charring have had many misconceptions.

The early texts on fire investigations promoted the use of identifying the varying degree of charring throughout the compartment to assist with origin determination. Rethoret () describes that the fire investigator should "study closely the depth of carbonization at various places, as this will bring the investigator in getting back to the point of origin". Straeter and Crawford () text identified that "the point of deepest char in the wood is likely to be the point of origin of the fire". Kennedy () relates that "wooden joists or studding are exposed to burning...the sides exposed to the direction from which the fire is coming will be more severely burned and charred". Prominent forensic scientist, Paul Kirk (), wrote in support of using depth of char for fire investigation in the following, "variations in depth of the char will inevitably be noted...and that this feature of the fire is of primary importance". None of these texts, however, provided a methodology to the reader on how to go about identifying what constitutes greater and lesser visible or measurable char damage.

Gypsum Wallboard / Drywall (Calcination)

Gypsum wallboard is one of the more common lining materials for walls and ceilings used for construction of residential and commercial facilities. Gypsum wallboard is a common structural lining material consisting of a core of gypsum (calcium sulfate dihydrate) sandwiched between two paper facers (McGraw and Mowrer ).

There are several effects that may occur to gypsum wallboard when exposed to heat and fire conditions, including: color changes, soot deposition, charred paper, paper consumed and clean burn (Fig. ). Determining which effect or effects reflect varying degrees of damage is the key to successfully assessing damage. Two methods are used to visibly interpret damage on gypsum wallboard (1) cross-sections of the wall can be evaluated for visibly identifiable changes to the gypsum wallboard through depth and (2) the surface effects can be evaluated for visibly identifiable varying DOFD.

Much of the earlier published research was focused on examining cross-sections of the wallboard, visibly determining the depth of calcination based on different bands of color within the cross-section (Posey and Posey ). The Posey study reported that an investigator could visibly identify subtle color changes in individually cut cross-sections of the wallboard and prescribe the DOFD associated with the color changes. Several researchers supported this analysis but questioned the practical application of such a method (Schroeder ; Kennedy et al. ). Other researchers have shown that the cross-sectioning method is misleading, as well as having significant procedural drawbacks (Mann and Putaansuu ; Mealy and Gottuk ). Most recent studies consider taking the actual depth of calcination by using an instrument and probing it into the wall a more effective method (Mann and Putaansuu, ; Mealy and Gottuk, ; Kennedy et al. ). Therefore, the visual identification of color changes through the cross-sectioning of wallboard will not be further addressed.

Measurable damage

Mealy et al. () designed a tool based on the previous work of Ngu (), which used a force gauge with an attached hex key probe (2 mm diameter). The Mealy, Wolfe and Gottuk study used the Ngu force gauge to ensure that the user performed their measurements with similar force (Mealy et al. ). They confirmed that 6.6lbf (3 kgf) of force was best at matching the Fourier Transform Infrared spectroscopy (FTIR) chemical analysis of dehydration found in the Mann and Putaansuu study (). The Mealy study () indicated that a variance on the depth measurements, regardless of the user, was negligible (~10 % variance) and that the method worked at reliably indicating fire travel, especially when no visible observations could be made. The Mealy, et al. study () also demonstrated that when visual damage to the wall surfaces were unable to provide enough data for analysis that contour plots of the depth measurements "provided valuable insight into the areas within the enclosure that were subjected to the most severe thermal damage, the areas in which the initiating (primary first fuel) fire occurred". This quote, however, is not to generalize that the area of origin is to be equated with the area of greatest thermal damage outside of this specific test series.

Although these studies demonstrated that depth of calcination surveys assisted in the area of origin determination, neither developed a process to quickly process a fire scene. The prescribed process by Mealy () was time consuming due to the requirement on the user to be extremely careful in watching the gauge and then marking the probe with a piece of tape to document the depth, thus introducing potential error.

The constant force is applied to the tool by two 3.3 lb constant force springs. The use of 2 springs running parallel to each other allows for equal pressure on each side of the tool (Fig. ). The measuring pin is constructed of a 2 mm cobalt drill bit. The pin size was based on the Mealy () research, which resulted in a pressure of 1175 psi (0.86 kg/mm ²). Resistance in the tool system is minimized through the use of UHMW-PE TIVAR plastic on all sliding surfaces, eliminating metal on metal contact. This includes the spring housing and rear slider block. This study also developed a simplified grid system out of tent pole stakes to decrease scene processing time.

Visible damage

Hicks et al. (; ) conducted a fire pattern reproducibility study using single fuel items. Forty-eight tests were conducted with a standardized ANSI/UL wood crib and ten additional tests were conducted with commercially available polyurethane foam recliners. The fuels were burned against a gypsum wallboard lining material within a compartment lined with gypsum wallboard. Twelve thermocouples were mounted in a grid array above the fuel item to capture temperatures for the duration of the tests. These two studies demonstrated a relatively predictable response of visible damage to the gypsum wallboard consistent with the varying DOFD identified in NFPA 921 (Figs. and ).

Madrzykowski and Fleischmann () performed a study of the response of gypsum wallboard and the reproducibility of the damage pattern created when exposed to known heat release rate (HRR) fires with varying types of fuel sources and wall construction. The fuels used for their experiments included a natural gas burner, gasoline pool fire and polyurethane foam. The wall construction was varied between a single sheet of gypsum wallboard with wood framing, a gypsum wallboard front and back with wood framing and gypsum wallboard front and back with fiberglass batt insulation in the voids of the wood framing. The gypsum wallboard was covered with a primer and cover coats of latex paint. This study focused on the effects where the paper had been burned away (consumed) and where the paper had been peeled up (penetration). To accomplish this, the researchers evaluated the variability of the flame height in comparison to the height and area of damage. As expected, the results indicated that the patterns generated by the polyurethane foam fire had greater uncertainty than the natural gas and gasoline pool fires. The wall construction had no significant impact on the damage.

Mann and Putaansuu () exposed samples of gypsum wallboard to three levels of heat flux for three different durations and noted visible changes, as well as depth of calcination changes with a variety of probing instruments. Their study reported that the fire damage to the surface and internal cross section of the wallboard occurs progressively in the following manner:

Mealy et al. () also discuss findings related to the visual identification of surface damage progression to gypsum wallboard based on imposed heat fluxes. They further confirmed the NFPA 921's and Mann and Putaansuu's progressive visible damage to the surface of the gypsum wallboard.

Riahi studied the soot deposition characteristics of three different fuels in bench-scale experiments and then against a gypsum wallboard lined wall (Riahi and Beyler ; Riahi ; Riahi et al. ). An optical measurement method was developed to arrive at optical properties of smoke deposited out of a smoke layer onto glass filters. From this work, the researchers used gravimetric measurements of these filters to demonstrate and validate an analytical model for smoke deposition based on thermophoresis. Consequently, a new optical measurement method was developed to use with digital photographs and digital image analysis. The researchers used ImageJ software and a Kodak gray scale and found good agreement between the optical measurement methods and smoke pattern images developed along wall surfaces. Their study showed that "the smoke pattern was determined for the wall tests and showed a difference between test conditions and very good agreement for the method for all test conditions" (Riahi ). They also stated that "based on the clean zone area, the flame height and the fire size can be calculated" (Riahi ). Finally, the study was conducted with a variety of digital cameras and they found that the optical properties were not dependent on the camera used.

Literature on identifying fire patterns

As one early fire investigation text declares, "patterns are the cornerstone of all fire investigation because of their universal applicability" (DeHaan ). It is important to evaluate the evolution of the term fire pattern to better evaluate what literature exists.

Fire pattern was first used to describe how the fire developed or had traveled as described by Kirk, "every fire forms a pattern that is determined chiefly by the configuration of the environment and the availability of combustible material" (Kirk ). The term or similar terms were later defined in subsequent texts as "where the fire's destruction took place and where it did not" (DeHaan ). In the United Kingdom the use of fire patterns can be found within the literature, though, they tended to discuss these as directional signposts where the "heat flow will cause asymmetric effects within the building" (Cooke and Ide ). These early definitions are broad and all encompassing of the entire fire scene. The first attempt at consolidating patterns was the first edition of NFPA 921, however many misconceptions had spawned up between the early 1960's and the publication of NFPA 921 (NFPA ).

The Law Enforcement Assistance Administration (LEAA) documented many of the myths about using the visible appearance of damage to identify arson (Boudreau et al. ). Arson investigators were surveyed about how they investigate fires and cited interpretation of "burn indicators" as the most common method of establishing arson. Some of these indicators used were alligatoring, crazing of glass, depth of char, lines of demarcation, sagged furniture springs and spalled concrete. The LEAA report, after listing the indicators, identified that these indicators have received little or no scientific testing and that "there appears to be no published material in the scientific literature to substantiate their validity" (Boudreau et al. ). Despite the lack of validity and this caution, the training and textbooks within the profession during this time used these indicators as a means to link an observation to the speed of the fire and ultimately to the conclusion of fire cause.

In 1992, NFPA 921's first edition identified most of these old indicators as misconceptions. This first edition was also the first time fire patterns were organized into one document. NFPA 921's original definition stated "fire patterns are the physical effects that are visible or measurable remaining after a fire...including thermal effects on materials, such as charring, oxidation, consumption of combustibles, smoke and soot deposits, distortion, melting, color changes, changes in the character of materials, structural collapse and other effects" (NFPA ).

The original definition of fire patterns and how it was used in NFPA 921 was all inclusive of the varying degree of damage to materials, clusters of damage, geometric shapes and the process of using damage to arrive at an area of origin (NFPA ). It was not until 2008 that NFPA 921 changed the definition of the term with the introduction of the term fire effects. The definition of fire patterns evolved to "the visible or measurable physical changes, or identifiable shapes, formed by a fire effect or group of fire effects" (NFPA ). The definition of fire effects became "observable or measurable changes in or on a material as the result of a fire" (NFPA ). Fire effects are the bases for the varying DOFD that was discussed in the previous section. This did not so much redefine the NFPA 921 coverage of the topic, but rather clarified the fire investigator's interpretation process in identifying a fire pattern.

The evolution in terminology clarifies how fire patterns became a more restricted definition and it is this bounded term that will be the focus of this literature review section. Prior to discussing the patterns themselves and their historical progression, it is first important to recognize that lines of demarcation or areas of demarcation serve as the borders of a fire pattern and should be defined. Areas of demarcation are locations along a surface that exhibit similar damage characteristics ( e.g. magnitude of damage, type of fire effect, color, texture) and are in close proximity to each other. Lines of demarcation are "the borders defining the differences in certain heat and smoke effects of the fire on various materials. They appear between the affected area and adjacent, less-affected areas" (NFPA ).

The fire testing conducted for fire patterns has evolved with the changing definition of the term. As such, a subsection on testing is first presented to describe all fire pattern tests conducted, not just those evaluating the current use of the term. The tests were typically conducted to evaluate multiple aspects of using damage for origin determination and not just within the context of clusters of damage, therefore, many of these tests will describe fire effects, clusters of fire effects, fire pattern generation and the use of fire patterns to arrive at an area of origin. The tests will be summarized chronologically in this section and will be referred to in other sections of the literature review where the work specifically addresses that subject matter.

Fire tests conducted related to fire patterns

All of the fire pattern studies have been summarized in Additional file . This spreadsheet provides all of the test details, general instrumentation results, list of indicators identified or not and provides the probability for the identification of these indicators.

The first published fire pattern tests was in 1984 (Custer and Wright ). Two 15 ft by 15 ft (4.57 m × 4.57 m) structures with a ceiling height of 7 ft (2.13 m) were tested. The compartments were of frame construction with unfinished wood lining the interior of the compartment. There were two windows and one door, where one window was closed and the other open for the fire duration, while the door was opened 5 min post-ignition. The open window was 3 ft by 3 ft (0.91 m × 0.91 m) with a sill of 2 ft (0.61 m) that was directly across the room from the doorway that was 3 ft by 6 ft (0.91 m × 1.83 m). Both compartments were furnished similarly with a sofa located under the open window, a sofa located along the wall next to the door and a kitchen table in the center of the compartment.

The origin of both fires was located under the window in the sofa, but different accelerants were used to start each test fire with 2-gallons of gasoline in test 1 and scattered newspaper in test 2. A thermocouple tree was located at the area of origin. Each test fire was conducted for 10 min, with the door opened at 5 min. The researchers report negligible winds on the day of the tests. Both tests resulted in an area of greatest damage directly across the room from the window opening, the opposite side of the room from the true origin.

This test was conducted as part of a conference where the participants of the conference were to evaluate the fire scenes for origin. It was reported, "many of the investigators had difficulty finding the location of the point of origin, in many cases indicating the opposite side of the room" (Custer and Wright ). The conclusion reached by the researchers was that "it would appear that the major conclusion which can be drawn from this study is that ventilation conditions in the early stages of a fire can cause an anomalous fire spread, thus giving a false impression as to the point of origin" (Custer and Wright ). The researchers consequently provide guidance to investigators on how to resolve this situation by saying "it is necessary to pay particular attention to low burns and shadow effects on room furnishings" (Custer and Wright ).

In 1997 The United States Fire Administration (USFA), in conjunction with the National Institute of Standards and Technology, Building and Fire Research Laboratory (NIST-BFRL) launched the fire pattern research committee and produced the USFA Fire Pattern Test report (Shanley et al. ). This project consisted of 10 separate full-scale tests to produce the first scientifically controlled and recorded research into the formation, growth and investigation of patterns produced in fires. These tests produced the first published data that supported fire patterns as being useful in fire investigation. However, this report also demonstrated that in two tests, "distinctive patterns were produced which without careful study and a full understanding of all factors which influenced the progress and growth of the fire, could easily be interpreted to indicate incorrect or multiple origins" (Shanley et al. ).

This study noted that flashover and ventilation was one of the most misunderstood variables, having the influence to alter "normal" fire pattern production. Most notably, "patterns which indicated areas of intense burning but were remote from the point of origin were observed and were determined to be from ventilation effects only. This was observed in rooms, which had flashover conditions where clean burn areas were produced under windows away from the origin. This was also observed on walls opposite door openings" (Shanley et al. ). Heat and flame vector analysis was used as a process within these studies to document the direction of fire travel, location and magnitude of fire patterns, as well as a process of confirming the area of origin. Again, no procedural details were provided on how to implement the heat and flame vector analysis, but this was the first time that formalized diagrams and legends were published as demonstrative aids.

In March of 1997 four full-size compartment test fires were conducted in furnished bedrooms (Milke and Hill ). The compartments were 12 ft by 12 ft with 8 ft ceiling heights (3.6 m × 3.6 m × 2.4 m) with a single door opening 3 ft by 6 ft-10 in. (0.91 m × 2.1 m). The rooms were instrumented with heat flux gauges, thermocouples and gas sampling probes. The burns were intended to be identical to determine if differences would be discovered with a close analysis of the results. In all cases, ignition of a gasoline spill next to an upholstered chair was used to initiate the fire. The researchers noted differences and attributed these to small variations in the inflow of air.

Another series of full-scale fire tests was conducted with funding provided by the National Institute of Justice (Putorti ). Putorti reported, "comparisons of the conditions of the rooms and furnishings after the experiments resulted in the determination of several similarities, as well as many differences, between experiments with the same method of ignition" (Putorti ). He attributes the differences to the "ventilation effects".

In 2003, ten full-scale test burns were performed in a ISO 9705 room 12 ft by 12 ft with 8 ft ceiling heights (3.6 m × 3.6 m × 2.4 m) with a primary focus on examining television sets and electronic appliances exposed to a full-scale room fire (Hoffmann et al. ). Six tests were completed with television sets placed inside a wood entertainment center. Two tests were completed with television sets placed on a wood stand next to an upholstered chair. These eight tests were "allowed to continue until just before flashover conditions were attained" (Hoffmann et al. ).

The ignition varied where four tests had a 2 ft (0.61 m) diameter pan of Isopropyl Alcohol (IPA) used to ignite a small electrical appliance adjacent to the television set, two tests were ignited by applying the IPA fueled fire directly to the television set and the last two non-full room involvement tests were ignited with the use of newspaper sheets under the cushion and on the floor in front of the upholstered chair. The final two tests were performed after "multiple television sets and electronic appliances were placed on wood stands and on the floor in a burn room containing an upholstered chair and area rug...both of these tests were allowed to progress into full-room involvement and were not extinguished until 4 min past flashover" (Hoffmann et al. ).

The researchers stated that one of the objectives of their tests "was to determine if burn patterns in the room were consistent with the origin or location of the external fire" (Hoffmann et al. ). The results for the eight tests that did not reach full-room involvement were reported as having "asymmetric fire patterns and heat damage was consistent with the location of the exposure fire for all but one pre-flashover exposure fire test" (Hoffmann et al. ). The one test that deviated showed a V-pattern emanating from the floor behind the entertainment center giving the appearance that the "fire origin could be interpreted to be located on or near the floor behind the entertainment center when the fire origin was to the left and along side the television inside the entertainment center" (Hoffmann et al. ). The researchers report this deviation in the fire patterns was caused by "the burning, melting and dripping of the plastic electronic appliance next to the television" (Hoffmann et al. ).

The two tests that resulted in full-room involvement showed that "burn patterns could be generated which were not indicative of the area of origin of the fire" (Hoffmann et al. ). In one of these tests it was found that "other burn patterns in the flashover tests showed similar misleading patterns from asymmetric burning of a television set, with the most damage on the side away from the origin of the fire to patterns on the gypsum walls indicating a V-pattern pointing to a television stand and associated electronics" (Hoffmann et al. ). The room burns produced patterns that were both consistent with the origin as well as burn patterns and V-patterns that were inconsistent with the origin.

Beginning in March of 2005, a series of 20 full-scale fire pattern tests were conducted at Eastern Kentucky University (Gorbett et al. ; Hopkins et al. ; Hopkins et al. ; Hopkins et al. ; Gorbett 2010; Gorbett et al. ). The test fires were conducted in identically constructed, finished and furnished living room and bedroom compartments within a burn building. These studies focused on fire pattern reproducibility, pattern persistence through flashover, the use of fire patterns in origin determination and the influence of initial, low HRR fuel on fire pattern production. The researchers discuss that similar truncated cone patterns were identified in the first eight tests (Gorbett et al. ). The most important finding from these tests is that "the interpretation of all fire effects provides substantial evidence for the investigator to identify the correct area of origin" ( Gorbett et al. 2010). These studies contended that the use of the heat and flame vector analysis enabled the investigator to determine the true area of origin. Fire effects were listed for each test, fire patterns identified and formal heat and flame vector analysis legends and diagrams were provided for each test. However, no procedural details were provided on how to implement the analysis.

In 2005 and 2008, three studies were completed in conjunction with a training seminar to analyze burn pattern development in post-flashover fires (Carman ). This study focused on the impact of ventilation on fire patterns and the ability of fire investigators to use fire patterns to determine the quadrant of the room where the fire began. The test was conducted in a single compartment measuring 14 ft by 12 ft by 8 ft high (4.26 m × 3.66 m × 2.4 m) that resembled a residential bedroom with one open doorway to the exterior. The fire was allowed to burn in post-flashover conditions for approximately 2 min. Clean burn damage located on the wall opposite of the door opening (not at the area of origin) extended from the floor to the ceiling and had an approximate 6-foot base. There was also an area of clean burn with angled lines of demarcation emanating from the area of origin.

Carman () divided the room into four quadrants and performed a survey of the attendees in an attempt to derive an error rate study of investigators. He reports a 5.7 % success rate of determining the correct quadrant where the fire was started. The Carman study did not provide the demographics of the attendees, nor did it provide any statistical rigor. Carman attributed the failure to the lack of understanding by the investigation profession of the differences between pre- and post-flashover fire behavior and resulting damage. The authors have since noted several limitations to this exercise including that the participants were not permitted to complete a full investigation of the compartment, were not allowed to move any items and had to make a conclusion based on their visual interpretation of the damage from the doorway.

In 2009, Wolfe, Mealy and Gottuk conducted 15 full-scale tests with varying ventilation conditions and fuels. They focused on under-ventilated fires, the fire growth associated with these types of fires and their forensic analysis. While much of the research was based more on the tenability limits and associated dynamics in under-ventilated fires, they reported on a few forensic-based conclusions. These included that soot deposition can be used to aid in the area of origin determination and that the clean burn area size was proportional to the fire size (Wolfe et al. ).

Carman reports on three tests conducted at ATF's fire research laboratory in a follow-up to his 2008 work (Carman ). The three tests were conducted with identical contents and ventilation. The compartment size, ventilation opening and setup were similar to the 2008 work. The three tests were better instrumented with three total heat flux gauges, one radiant heat flux gauge, three gas sensors (measuring O ₂, CO ₂, CO), and gas velocity probes (Oullette ). The tests were able to burn in the full-room involvement state for 7, 140 and 111 s respectively. Each test fire resulted in damage along the wall opposite of the door opening, progressively greater in magnitude with the longer duration in full-room involvement burning. This area of damage opposite the door had angled lines of demarcation that extended from the floor to the ceiling. A clean burn area of damage was located at the area of origin only with the fire with the shortest duration of full room involvement burning. Clean burn damage also occurred along the wall near the doorway opening in the fire with the longest full room involvement burning duration.

A series of nine full-scale studies, funded by the National Institute of Justice, were conducted with ignitable liquid fuel spilled on carpeted and vinyl flooring with varying ventilation scenarios (Mealy et al. ). These tests evaluated many aspects of fire investigations, including the presence of ignitable liquid residue after extinguishment, fire patterns, depth of calcination and the fire dynamics of an under-ventilated compartment. A compartment (3.7 m × 3.7 m × 2.4 m) with a single doorway ventilation opening located in the center of a wall was used for this series of tests. An upholstered sofa and upholstered chair were located in adjacent corners across the room from each other with a coffee table in between. The ventilation opening was located in the wall opposite of this furniture. The ventilation opening was varied throughout the test between a slit vent (2 m × 0.2 m) and the full door opening (2 m × 0.9 m). Test one used only Class A fuels, while the eight remaining tests used gasoline as the first fuel ignited. The location of gasoline spilled was varied between the floor and on/around furniture items.

Some of their more notable findings was that floor patterns caused by ignitable liquids may be minimal because they can easily be destroyed, that the commonly reported clean burn damage may be caused by water spray from fire suppression hoselines and that areas of clean burn were associated with the inflow of air due to local ventilation flows. Mass loss of the furniture items was measured at the end of each test and was showed to relate well to the area of origin. Areas along the wall surfaces that were white in color directly adjacent to areas of significant soot deposition were found within this series of tests to be attributed to the oxidation of the soot from the surface ( i.e. clean burn) and with wash from the hoseline for suppression. Also, the study illustrated that drywall seams, if no tape and mud was applied, would present areas of clean burn damage during ventilation-controlled conditions (Mealy et al. ).

In 2011 three test fires were conducted that varied between single and multiple ventilation openings (Claflin ). The three compartments were similarly constructed measuring 11 ft, 5 in. by 11 ft, 9 in. (3.48 m × 3.58 m) with a ceiling height of 8 ft (2.4 m). Each compartment had a door that measured 2 ft, 7 in. by 6 ft, 8 in. (0.787 m × 2.032 m) and was opened to the exterior for the entire duration of the test. Two tests also had a window that measured 3 ft by 4 ft in height (0.91 m × 1.22 m) with a 2 ft, 6 in. sill height (0.812 m). The compartment was furnished as a residential living room with a couch under the window, armchair directly across the room from the door opening, an office chair adjacent to the doorway and a coffee table.

The origin and ignition of the three tests were in a pillow placed along the back corner of the couch on the floor against the wall with the window. Each fire was said to have only burned for 2 min in full room involvement. Thermocouple data and total heat flux gauges were used as instrumentation for all three burns. Test 1 had the window and door open for the entire duration of the fire, test 2 had the window hinged closed until flashover and then the window was left opened for the duration of post-flashover and test 3 had no window. These tests demonstrated similar findings as Carman's tests (2008) that significant heat flux and clean burn occurs on the wall directly across the room from the doorway. There was no significant damage identified around the window ventilation, as the researchers discussed that this vent served primarily as an outflow for the heated gases, while the doorway served as the inflow due to the location of the neutral plane. The researchers also concluded that the fire pattern at the true origin persisted in all three tests.

Fire patterns

This section focuses on the literature that exists for fire patterns. This section has been divided into four subsections that evaluate the general location and type of fire patterns.

Undamaged areas

Penetrations

Holes in floors have had many misconceptions tied directly to floor patterns, as discussed previously. The same proponents of identifying 'pour patterns' as being indicative of an ignitable liquid, also promulgated that holes in floors were indicative of ignitable liquids being used (Battle and Weston ; Fitch and Porter ; Barracato ; Smith ; Harmer et al. ; Kennedy and Kennedy ; Cooke and Ide ). Kirk being one of the few texts at the time that opposed this idea when declaring "flammable liquids never carry fire downward" (Kirk ). As floor patterns were warned against, so has floor penetrations by both the fire science and investigation communities (Babrauskas ; NFPA ). Alternative explanations are now commonly given when discussing penetrations through floors, including: radiant heat, furniture items, melting plastics and pre-existing openings in the floor during fully involved compartment fire (NFPA ) (Fig. ).

Babrauskas () lists several unpublished tests of holes through wood floors and provides a summary of these tests.

Literature on compartment fire dynamics influencing damage

The damage observed to wall, ceiling and content surfaces is an artifact of the fire dynamics for that fire. Identifying the cause of the damage is complicated by the fact that the investigator has to use evidence after the event, such as the location and magnitude of damage, compartment geometry, ventilation openings and the position and number of fuels as a means to identify the range of initial conditions that may have influenced how the fire developed. Because of this, the problem of using fire damage to determine how the fire developed is considered an inverse problem. Other areas of science regularly deal with inverse problems typically through extensive mathematical study. However, most inverse problems are approached by first establishing direct solutions for well-posed problems. Therefore, the approach of this step is to leverage what science currently exists to assist with validating the current list of direct solutions for fire pattern generation and identifying characteristics that may exist and how they may vary with the changing fire dynamics. The direct solutions currently listed for causes of fire patterns include, plume-generated patterns, hot gas layer-generated patterns, ventilation-generated patterns and suppression-generated patterns (NFPA ).

In this section of the literature review, sections 2.3.1.1-2.3.1.2 discuss the basic causes of fire patterns and will serve as the connection of fire investigation terminology to the fire science research that has been conducted in those areas. Section 2.3.2.1-2.3.2.5 will outline the characteristics that are currently being used by fire investigators in determining the cause of the fire pattern and evaluate the findings of the fire pattern studies.

Causes of damage

The investigator typically assigns an interpretation to each fire pattern as to how it may have been created, which in turn assists the investigator in determining how the fire spread. This process has significant potential for uncertainty, as the initial conditions are generally unknown to the investigator.

NFPA 921 states that there are "three basic causes of fire patterns: heat, deposition and consumption" (NFPA ). Consumption is a function of heat transfer and the material properties. As such, material properties were already discussed in the degree of fire damage assessment and will not be duplicated here.

Cause of damage - heat

The cumulative heat exposure should be considered the leading factor in the creation of damage. The cumulative heat exposure consists of the duration and varying intensity of heat exposure to the materials. Heat exposure to the materials ( e.g. plastics, wood) will result in either physical or chemical changes. Physical changes include melting, deformation, expansion, or loss of tensile strength. Chemical changes include the decomposition/pyrolysis, dehydration, or changes in color.

Heat damage to the surface linings and the contents within the compartment after the fire is frequently the most readily visible and measurable. The effects that remain after a fire are typically related to the damage resulting from the cumulative heat flux received by an exposed material. The developing fire and the variables influencing the fire scenario control heat transfer in a compartment, including the location, the intensity and duration of the heat transfer. The dominant sources for heat transfer during a compartment fire stem from the following:

As heat transfer is first and foremost dependent on a temperature difference, greater temperature differences will result in greater heat flux. In a compartment fire, the highest temperatures are present at those locations where flaming combustion is occurring. The fire plume and the various heat fluxes generated by it are one of the primary means of damage production in the early stages of a fire due to this great temperature difference and highly turbulent flows. Fire plumes against wall surfaces have shown to have moderate heat fluxes ranging from 40 to 80 kW/m ², while heat fluxes measured in tests with objects immersed in diffusion flames range between 75 and 200 kW/m ² Heskestad (); (Qian and Saito ; Dillon ; Lattimer ). Incident heat flux to wall, floor, or ceiling surfaces is dependent on the HRR of the fuel and standoff distance between the flame plume and the surface of interest. The greater the distance between the base of the plume and the surface of the wall or content surface will result in a substantially decreased heat flux to the surface (Qian and Saito ). Saito (); Williamson, et al. () witnessed a 50-70 % decrease in peak heat flux values when small standoff distances (0.05-0.25 m) were employed.

One aspect of looking at radiant heat flux is to determine if the secondary object has been raised to a critical temperature or is receiving a critical heat flux where ignition of that object is possible. In the fire investigation profession, testing to determine whether the first burning object can ignite a secondary object is paramount to hypothesis testing of an area of origin. Equally important is to determine whether the radiant heat transfer is sufficient to cause damage to nearby contents or wall surfaces.

Babrauskas () reports on ignition of secondary items based on burning a series of common residential fuels and evaluating the heat flux to transducers at varying lateral distances. He reports

"irradiances measured 0.05 m away range to near 80 kW/m ² for the fastest burning specimens; however, 40 kW/m ² was not recorded farther than 0.44 m away and 20 kW/m ² was not found beyond 0.88 m distant. The implication is that common furnishing items, which normally require a minimum irradiance approaching 20 kW/m ² for ignition, would stand little hazard of fire involvement if placed at least 1 m away from the initial source" (Babrauskas ).

These findings were reported as only being applicable for pre-flashover fires. More recent research has identified heat flux values between 25 and 50 kW/m ² reported at 1 m away from more modern fuel packages, including king size mattresses, upholstered chairs and sleeper sofas (Madrzykowski and Kerber ).

The collection of high temperature gases within a compartment is also a source of heat flux that can cause damage. A ceiling jet is formed by the intersection of the plume with the ceiling, which will cause greater heat to be transferred first to the ceiling surface and later to the intersecting wall surfaces. The temperature of the plume will be greatest near the plume centerline and therefore the greatest heat flux to the ceiling surface will be at this location at this point throughout the duration of the fire. The temperature and resultant heat flux decreases with increasing radial distance from the plume centerline. In addition, the ceiling jet velocity is highest near the centerline of the plume and decreases as it moves outward (Heskestad ). Consequently, these two factors combine to inflict more damage and create more pronounced fire effects near the plume centerline, with the damage decreasing as the distance from the centerline is increased (Jowsey ). When the flame plume has not intersected the ceiling, heat fluxes along the ceiling surface near the centerline of a plume have been recorded to range between 80 and 100 kW/m ² within 0-1 m radial distance, while heat fluxes between 1.0 and 1.6 m radial distances ranges between 10 and 70 kW/m ² (Dillon ; Lattimer and Sorathia ).

As the fire continues to develop, the ceiling jet and the gases from the upper layer begin to have an intensified effect on the surfaces nearest the plume. Later in a fire's development, an upper layer begins to form and starts transferring heat to the wall and ceiling surfaces. The energy generated by the fire and therefore the temperatures and layer depth of the upper layer vary as a function of time (Walton and Thomas ). Thus, different locations within the compartment may be receiving different temperatures at different times throughout the fire. However, an assumption can be made for fuel-controlled fires that higher temperatures will occur at the plume interface with any building or content's surface. As the temperature of the gases in the upper layer increases and the duration of influence between these gases and the lining surfaces increase, the heat flux imposed on these surfaces reaches a critical threshold that begins damaging the material and creating fire effects attributed to the upper gas layer. Heat fluxes to the walls inside a compartment containing an upper gas layer have been reported to range between 5 and 40 kW/m ², based on varying temperatures between 200 and 600 °C (Tanaka et al. ).

Drysdale () indicates that the average compartment temperatures are highest near the cross over between fuel-controlled and ventilation-controlled. The fires that are located at the extremes of the spectrum ( i.e. predominantly fuel-controlled or ventilation-controlled) produce substantially lower temperatures. Consequently, the damage expected in a fuel-controlled state is generally less-severe until the ventilation begins deteriorating, nearing the cross over to ventilation-controlled. Furthermore, average fire gas temperatures have been related to the ventilation factor compared to the total surface area of the compartment, commonly denoted by \( {A}_v\sqrt{H_v}/{A}_T. \) This relationship points out that there are higher gas temperatures reached in the fuel-controlled burning but the duration of burning is shorter because "much of the heat energy is transferred out of the room by the air/fire gas exchange" (Drysdale ).

There has been extensive work done in the area of flashover for traditional residential-sized compartments with a single opening. Several correlations have been developed to assist in determining the minimum HRR necessary for flashover to occur, conditioned on the total surface area of the compartment (A T) and the ventilation factor \( {A}_v\sqrt{h_v} \) (McCaffrey and Quintiere (); Babrauskas ; McCaffrey et al. ; Thomas ). As the compartment transitions through flashover and into full-room involvement, the upper layer descends toward the floor and encompasses nearly the entire volume of the compartment. Therefore, the walls, ceiling and floor surfaces are now receiving an elevated heat flux, in addition to the already burning fuel receiving greater feedback, increasing its own HRR and other fuels becoming involved. A common maximum recorded heat flux in a postflashover compartment fire is 170 kW/m ² (NFPA ). Each fire pattern study has the three most common flashover correlations summarized within Additional file .

During a fully involved compartment fire or when a compartment fire is ventilation-controlled, more complete combustion is achieved at those locations where the mixture is adequate. Several studies concerning ventilation-controlled fires throughout the years have introduced a concept of a ventilation factor (\( {A}_v\sqrt{h_v} \)) and illustrated the importance of ventilation openings on a fire's growth by analyzing the size of ventilation openings, locations of these openings within the compartment and the shear mixing that occurs at the interface of the opening (Kawagoe ; Thomas and Heslden ; Harmathy ; Thomas and Bennets ; Utiskul ; Sugawa et al. ; Quintiere ). Many of the studies discuss the production of unburned hydrocarbons (UHC's) during under-ventilated conditions that result in unburned fuel filling the compartment and undergoing combustion only where sufficient UHC concentrations encounter sufficient oxygen (Beyler ; Utiskul and Quintiere (); Utiskul ; Thomas and Bennets ).

Not all compartment fires will transition through flashover (Drysdale ). The compartment can reach a state of full-room involvement without transitioning through flashover, or become ventilation-limited and never achieve full-room involvement state (Francis and Chen ). One of the most important findings is that combustion was found to occur detached from fuel items and found to burn nearest the open ventilation source if the global equivalence ratio ( ϕ) in the fire room becomes larger than unity, typically between 1.2 and 1.6 depending on temperature (Thomas and Bennets ; Utiskul ). ϕ is defined as the average fuel-to-oxygen mass ratio in a compartment divided by the stoichiometric value in a compartment (Wieczorek et al. ).

The fire is generally regarded as well-ventilated when values of ϕ < 0.3 − 0.5. The combustion within this compartment is of a high efficiency and the yields of soot and carbon monoxide (CO) are low (Pitts ). The fire is considered to be under-ventilated at higher values of ϕ > 1.0. Typically, flashover occurs at a ϕ = 1.0 (Wieczorek et al. ). Gottuk () reports sustained external burning occurring at ϕ values around 1.4 +/−0.4, but other research has reported extension of flames outside the compartment starting at ϕ values of 0.7 (Wieczorek et al. ). Gottuk's () results were gases from the layer burning and escaping, while Wieczorek et al. () had flames resulting from a lack of mixing within the compartment, which has also been identified in compartments with combustible linings (Drysdale ). As the combustion zone is not attached to a fuel item or fuel package any longer, it becomes more difficult for the fire investigator to evaluate whether the damage was caused by a flame plume burning attached to a fuel item or if it is the UHCs burning detached from a fuel item due to ventilation-controlled conditions. Therefore, determining if and when the fire transitions from a fuel-controlled to a ventilation-controlled condition is an important distinction.

As the effects of ventilation have been shown to significantly influence damage within the compartment, a further review of these concepts is necessary. Hydrostatic pressure differences at the ventilation opening cause the hot gases to exit the compartment and cooler air to be transferred into the compartment, assuming no external force is causing a greater pressure. The natural convection drives air out of the compartment creating a lower pressure for inflow to be driven from gravity flows or can also be influenced by wind or other mechanically induced flows ( e.g. positive pressure ventilation). The mixing of the air and UHCs has been shown to occur at the opening, along the gravity flow, around objects within the flow and opposite the opening along walls, specifically for doors (Abib and Jaluria , ; Quintiere and McCaffrey ).

Cause of damage - deposition

Exposure of materials to the byproducts of combustion can also lead to damage that may be useful to the investigator. Smoke contains particulates, liquid aerosols and gases (NFPA ). The deposition of smoke/soot onto surface linings and contents within an enclosure stems from the following:

Combustion that fire investigators will most commonly encounter is predominantly diffusion flames. The combustion of a fuel through diffusion flames is inherently oxygen limited by the diffusion reaction and the availability of only 21 % of oxygen in air in well-ventilated fires. This limitation of the flaming combustion allows for the production of smoke. Smoke consists of liquid aerosols, solid particulates ( i.e. soot), and gaseous byproducts, including carbon monoxide (CO), carbon dioxide (CO ₂), hydrogen cyanide (HCN), oxygen (O ₂), steam (H ₂O vapor), and unburned hydrocarbons (UHC). This production of incomplete combustion byproducts is exacerbated in poorly ventilated spaces, ventilation-controlled burning regimes and combustion of fuels that under normal atmospheric conditions have high soot yields ( e.g. aromatic and unsaturated hydrocarbons).

Thermophoretic forces between the gas and surface lining are greatly dependent on the burning regime of the fire. In the early stages of a fire and through fuel-controlled conditions, the production of the incomplete combustion byproducts (HCN, CO, UHCs) is typically minor. The production increases substantially as the compartment fire becomes ventilation-limited. The higher temperatures and higher velocities of smoke cause greater collection of soot deposits to form in certain locations within the compartment. As the temperatures are higher in the room of origin it is expected that an upper layer will be affecting those surfaces higher in elevation. Conversely, as the smoke moves away from the room of origin the temperatures will decrease, which causes the smoke to descend within the compartment causing lighter soot to deposit across the entire elevation of wall surfaces. Therefore, it is expected that soot deposition on wall surfaces to be greatest in thickness and higher in elevation closer to the room of origin and lesser in thickness and lower in elevation as one moves away from the room of origin. Often times the soot deposited within the room of origin will be higher in elevation with distinct lines of demarcation and thick soot deposits. Soot deposited in rooms away from the room of origin have a fairly uniform soot deposition on all surfaces extending from floor to ceiling (Wolfe et al. ).

Riahi () studied the soot deposition characteristics of three different fuels in bench-scale experiments and then against a gypsum wallboard lined wall. An optical measurement method was developed to arrive at optical properties of smoke deposited out of a smoke layer onto glass filters. From this work, the researchers used gravimetric measurements of these filters to demonstrate and validate an analytical model for smoke deposition based on thermophoresis.

Characteristics of direct solutions

The characteristics of damage that have been reported in the literature to assist investigators in determining the cause of the fire pattern will be evaluated here.

Plume-generated fire patterns (PG Patterns)

Fire plume generated fire patterns are the most important to identify correctly. The fire origin will ultimately be connected to a plume generated fire pattern. However, if the fire pattern is incorrectly assigned as a plume generated pattern, then the entire origin hypothesis will most likely be incorrect (Carman ).

As with anything, there are additional caveats in the identification of plume-generated fire patterns. The first of which is the standoff distance between the fuel item burning and the damaged surface. Shanley et al. ()) reported one of the driving factors for the lack of a plume-generated fire pattern associated with the origin in a chair was due to the chair being placed approximately 18-inches away from the wall.

Dillon () indicated that one could generalize a simplified flame shape based on a series of ISO-9705 room corner tests by using the average incident heat flux of 30 kW/m ². He found that the damage from the flame plume would extend approximately the width of the fuel for 100 kW fires that did not have a ceiling jet form and 3 times the width of the fuel with 300 kW fires that did have flame extension under the ceiling. Dillon () went on to illustrate that some of the corner flame height approximations resulted in 40 % uncertainty, but others were as close as 2 %.

A conical pattern has been characterized as one that is produced when the interacting buoyant fire plume is restricted by an intersecting horizontal surface, spreading the heat across the bottom of the obstructing surface. The surface then redirects the buoyant flow and its momentum across the bottom of the ceiling creating a ceiling jet, which begins to descend from the ceiling as an upper layer (Hicks et al. ). This causes the plume to widen horizontally in the upper layer causing damage to the intersecting surfaces. A two-dimensional fire pattern is expected to form on the vertical surface interface ( i.e. walls) in the form of a funnel or cone with the vertex at the bottom. This fire pattern has been proposed to indicate a fuel package that has reached a HRR sufficient to create a flame plume that reaches the horizontal surface ( i.e. ceiling).

In summary, the characteristics distilled from the literature is that plume-generated patterns have areas of greater magnitude of damage in relationship to the surrounding areas and because of this the lines of demarcation between these areas are described as clear or sharp. Also, the lines of demarcation are not parallel to the floor or ceiling, but are at an angle representing the buoyant flow, usually with characteristic geometric shapes (Fig. ).

Upper layer-generated fire patterns (ULG Patterns)

Secondly, these patterns are often used as a means to show direction of smoke and heat travel.

The upper layer gases are elevated in temperature and have the ability to radiate heat downward onto the tops of contents throughout the compartment. Fire investigators describe this consistent damage to tops of contents as radiant heat damage being caused by the upper layer. Correspondingly, this heat source is often attributed to igniting contents throughout the compartment, especially those items located relatively high in elevation around the compartment ( e.g. curtains). Fire investigators commonly use the lack of thermal damage behind or under contents, known as protected areas, as evidence that the damage was caused by an upper layer.

Investigators use the varying heights and direction of the lines of demarcation as indicative of directional flow. Direction of flow is typically associated with the lower line of demarcation being closer to the origin of the flow. These patterns are often witnessed on vertical surfaces of content items and wall linings. The cited basis for this pattern is the principles of fluid flow and the buoyant nature of heated gases. This is the reason that many fire investigation texts commonly refer to fire moving up and outward (DeHaan and Icove ; Kennedy ; Kennedy (); Kirk ; Rethoret ).

When the gases rise and expand, they begin interacting with the lining surfaces and contents in the flow of the fluid. Particulates and aerosols are deposited and heat is transferred in the same direction and flow as the smoke. As the gases rise and expand, they also begin to interact with ventilation openings. The movement of smoke from a compartment into an adjoining space is controlled by the density differences at the interface of the ventilation opening. Upper layer gases inside the compartment are driven by density differences due to their higher temperature and lower density. These gases are buoyant compared to the surrounding air at the opening interface, which causes them to flow through the opening, unless there is wind or some other external force (mechanical ventilation) allowing the pressure outside of the compartment to be higher. Therefore, the dynamic forces that drive flow through an opening are based on fluid dynamics and fluids in motion at the ventilation opening interface and the discharge characteristics of the opening. As the smoke exits the opening, it expands in volume and rises. Particulates and aerosols are commonly deposited on the wall and ceiling surface where the upper layer interacted with the lining surface (NFPA ). In addition, if these gases were undergoing flaming combustion as they exited the opening, thermal damage to the wall surface is expected to follow the same theory (DeHaan and Icove ). The resulting damage appears to be angled lines of demarcation with the lower end of the line of demarcation being nearest the source of the smoke flow (Fig. ).

Characteristics distilled from the literature related that the ULG patterns will have level lines of demarcation with relatively uniform magnitude of damage, unless the upper layer is flowing from one location to another and, if so, the lines of demarcation will be angled towards the opening.

Ventilation-generated fire patterns (VG Patterns)

The more significant issue with ventilation-generated patterns is when the compartment fire is ventilation-controlled. During this phase of the compartment fire, there are adequate UHCs produced, but lack sufficient oxygen for combustion. The burning during ventilation-controlled conditions is often times detached from a fuel item ( i.e. wood chair) and the pyrolyzates (unburned fuel) will burn in locations near ventilation openings and along airflow paths when sufficient oxygen for combustion exists (Custer and Wright ; Shanley et al. ; Carman ; Gorbett et al. 2010). Consequently, temperatures in the upper layer will also vary based on local variations in this combustion. A substantial degree of damage is often times found directly adjacent to or opposite of window and door openings. This type of damage was noted in the USFA study with specificity (Shanley et al. ).

Shanley et al. () noted that the effect of ventilation was the one factor least understood and that ventilation-generated patterns were identified to be of great magnitude, sometimes greater than that of the patterns caused by the plume or origin. Their study noted that clean burn areas were observed on wall surfaces under windows that had opened during the fire and that the damage extended from the sill of the window to the floor. Also, their study noted that similar areas of great magnitude of damage occurred around doors and on walls opposite door openings.

Mealy et al. () identified similar effects near ventilation openings in their compartment fire tests. They identified areas of damage with greater magnitude around the doorway openings. In addition, this study identified that greater damage (clean burn) occurred at the seams between drywall sections within their tests when they were not covered with tape and mud, due to leakage through the unsealed openings. This same damage near the drywall seams was identified in the Claflin study () (Fig. ).

Characteristics of the damage linked with ventilation-generated patterns during ventilation-controlled conditions are large surface areas and increased magnitude of damage, angled lines of demarcation located around the ventilation opening or directly opposite of a door opening. Also, damage may be found near the unsealed seams of drywall sections due to infiltrating air.

Suppression generated fire patterns (SG Patterns)

Suppression factors may also impact the visible and measurable damage that investigators use. These factors included the location of water application, duration of fire burning prior to arrival, duration required to extinguish the fire, location of fire department entry, method of extinguishment, use of positive pressure ventilation ( i.e. forced convection, mechanical movement of smoke or spreading of contaminants), the change of ventilation upon arrival (breaking windows, opening doors, cutting holes in ceiling), and overhaul after the fire has been extinguished.

Mealy et al. () identified hose spray from suppression efforts as washing off areas of soot and ash from the gypsum wallboard, leaving behind a white area. These white areas were similar in appearance to clean burn patterns at first glance, but were shown upon closer examination to be differentiated based on smeared, directional appearance with observable water drip marks.

Many of the firefighting factors would not necessarily develop new patterns that have unique characteristics. For example, the location of fire department entry, the use of positive pressure ventilation and the change of ventilation upon arrival should result in fire patterns that are similar to ventilation-generated fire patterns. The only point of contention then would be the manner in which the ventilation opening was created. Finally, an area that is white in color surrounded by soot areas should not be classified as a clean burn area until closer examination is performed.

Alternate causal factors

Andrew Cox () argues that both the generic causal factors and the contextual circumstances should be considered when interpreting the cause of the damage. Cox provides an example where using these two concepts demonstrated that a white area on a wall required consideration of the causal factors and contextual circumstances to adequately evaluate the damage. He lists causal factors for this white area of damage as possibly hose stream wash, surface paper burned off leaving a 'clean' noncombustible surface behind, or the wall may have been surfaced differently prior to the fire ( i.e. repairs of the drywall performed). He then indicates that the contextual circumstances should also be evaluated, which include a relationship to other artifacts and associated casual factors (proximity to a fuel item), post-flashover conditions and proximity of damage to a ventilation opening. The changes to the wall surfaces by the owner through repairs and other possible information that may change the overall damage within the compartment need to be addressed.

Drywall repairs, as well as tape and mud between drywall seams or the lack of this material may alter the observations of damage in these areas and will need to be considered. Several researchers have identified significant changes in damage around drywall seams (Claflin ; Gorbett et al. 2010; Mealy et al. ). If the mud and tape were present to cover the drywall seams, then typically the damage is lesser at this area. However, if the mud and tape are not present and the compartment transitioned to a ventilation-controlled fire, the damage around these sources of ventilation may be significant (Claflin ; Mealy et al. ) (Fig. ).

Literature regarding the practice of using damage in fire investigations

This section of the literature review focuses on the use of fire patterns and fire pattern generation to identify an area of origin. Since the beginning of fire investigations, the focus on how to determine the area of origin for a fire was to try and use damage to work backwards in an attempt to recreate the development of the fire within the investigator's mind. Many of the early texts discuss this similarly to Rethoret when he states "using the method of tracing the course of the fire and by working backwards, the actual place where the fire originated can usually be determined by the greatest damage" (Rethoret ). In essence this shows that fire investigators were trained to identify the greatest area of damage and that this would be the area of origin. However, even the earliest text on fire investigation cautions investigators that ventilation may cause trouble with this process as it will cause greater damage in those areas of better "air currents" (Rethoret ). The earliest texts (Rethoret ; Kennedy ), however, do not offer a process on how to use the data, other than vague descriptions on visibly identifying greater areas of damage and tracing varying char damage.

The first identified process was published in 1955 (Straeter and Crawford ). The authors stated that "fire leaves its fingerprints and that each finger of flame leaves its effects and the study of these effects will help you pick the spot where it burned first" (Straeter and Crawford ). To accomplish this goal, the authors suggested that the area of origin could be identified through the use of damage by both (1) retracing the fire's path by the forces bearing on it and (2) retracing or reconstructing the path of the fire by the effects produced. The forces bearing on the fire were identified in this text as (a) combustibles involved, (b) openings and ventilation, (c) winds and drafts, (d) explosions and (e) variations from normal burning. The most emphasis was placed on combustibles involved and openings and ventilation.

The authors suggested that the investigator could evaluate the items involved and "the differences of flammability of combustibles along the route of travel may explain the route of travel or spread" (Straeter and Crawford ). They also discussed that locations and conditions of ventilation openings as functioning in "two different capacities, where the fire could pass to the next room...or it may be a source of incoming air to feed the fire" (Straeter and Crawford ). The second way to retrace the path of the fire towards the origin was by the use of the effects produced, which they broke down into evaluating six parts including (a) char, (b) remains and debris, (c) room temperatures, (d) sequence of shorted electric circuits, (e) sequence of sprinkler eruptions, (f) interiors of partitions and (g) adjoining properties.

The section on char suggested that the investigator go backward from the areas of "little char to deeper char establishing the path of fire clearly" (Straeter and Crawford ). They also suggested that the level of heat lines on the walls may be "traced back from the termination point toward the beginning...ordinarily they will be lower and lower on the walls as you approach the areas where the greatest heat was generated" (Straeter and Crawford ). This combination of using damage in the context of the fire behavior variables was new to the profession in 1955, but then apparently lost for the next 40 years. The authors do not, however, indicate how, provided this information, an investigator arrives at a conclusion.

The next identified process was promulgated by John Kennedy in 1962 and was termed the Pointer or Arrow Theory (Kennedy ). The pointer theory was proffered as a "system of determining the point of origin of a fire by tracing its path back to its source...the system is based on the fact that fires normally travel by feeding on flammables. The sides exposed to the direction from which the fire is coming will be more severely burned and charred. This will leave a series of burned studs, which serve as pointers or arrows to trace the fire" (Kennedy ). Again, Kennedy makes the argument that the investigator needs to identify the greatest area of damage. Kennedy incorrectly makes the assumption that "in fires involving buildings or other structures where wooden joists or studding are exposed and burning, the application of the fire will usually be constant" (Kennedy ).

Kirk was the next to put forward a general process on how to identify the area of origin based on damage. The focus of his process was similar to the others in describing that the area of origin will be located at the greatest area of damage and the investigators should focus on identifying the low burn damage areas and using conical shapes. He encouraged investigators to focus on low burns, because as he says "any low point in a burn should be investigated as a possible origin" (Kirk ). However, Kirk also identifies many of the "very common complications" that can arise, which will "distract the investigator from following the fire pattern back to its point of origin" (Kirk ). These deviations from 'normal' patterns, as he called them, included areas of open ventilation, secondary ignition of falling material, roof or attic fires, exterior exposure fires and roof collapse. He succinctly describes his process as "direction of spread of the fire will be noted...it will be upward, partially lateral, rarely downward, but its direction will indicate the general region of origin when properly interpreted. This should and generally is, close to the low point of the burn" (Kirk ).

Kennedy and Kennedy () described a first method as "the 'V' pattern method is based on the fact that fire burns upward and outward toward available fuel, leaving a 'V' shaped pattern that can be traced back to its lowest point which would be the area of origin". The only method that appears to be systematized and examples provided was the truncated cone method in conjunction with the heat and flame vector analysis (Kennedy and Kennedy ). This method was used to identify each fire pattern within the compartment, ascribe a direction or intensity to that damage and assign a directional arrow on a diagram to reflect this damage, however, no specific procedural details were provided on how to implement this analysis or how to interpret direction (Kennedy and Kennedy ).

In 1985, Cooke and Ide put forward a process termed radius of error (Cooke and Ide ). Their method encouraged investigators to use fire patterns to arrive at an origin, but upon arriving at their hypothetical area(s) of origin required the investigator to provide some measure of accuracy in the form of a radius of error. Their example is as follows, "if the investigator decides he has located a seat of fire within a radius of error of 1 m, he is certain that the original seat of fire lays within an area having one metres [sic] radius ( i.e. within an area of 3.14 square metres [sic])" (Cooke and Ide ). Their use of this method was stated to ensure that an investigator would be required to provide an indication of the degree of accuracy, as well as provide an area for excavation. This was the first time that investigators were encouraged to assign some reliability to their origin conclusion, however, the authors failed to provide guidelines on how specifically to arrive at the initial origin hypothesis.

Since 1992, NFPA 921 has established the de facto standard of care for the fire investigation profession, yet it lacks specific procedures for origin determination (Gorbett and Chapdelaine ). The only procedural aspect that NFPA 921 provides for fire pattern use for origin determination is the heat and flame vector analysis (NFPA ). However, no specific details are provided on how to implement this analysis. The scientific method is proclaimed throughout the document as the generic process for investigating a fire, but no specific procedural details are outlined on how to implement it into practice for analyzing fire patterns.

In 1997, a formal heat and flame vector analysis was conducted with three of the USFA fire pattern tests. The results confirmed that the use of this method was appropriate for these three test fires (Shanley et al. ). This was the first published work that outlined how to develop a legend and diagram as demonstrative aids for applying the heat and flame vector analysis. It can be argued that this study was the nearest any of the methods have come to being testing for reliability or validity (Fig. and Table ).

In 2002, fire pattern analysis was identified as an essential area of research by the National Fire Protection Association's Fire Protection Research Foundation. In their report, authored by its Research Council on Post-Fire Investigation, they recommended, "if patterns are to be used for origin and cause determination, forensic methods to identify the specific source of a pattern need to be developed and rigorously vetted" (NFPA, , p.5).

The first insistence that decision analysis should be considered for fire patterns analysis was in 2010 ( Gorbett et al. 2010). The study divided the use of fire patterns into fire effects and fire dynamics attributes and called for some form of weighting of fire dynamics attributes in the overall decision process. However, the authors did not propose a working prototype.

A survey was conducted to evaluate the proficiency of professional fire investigators at determining the area of origin when provided with photographs and measurable data from a test (Tinsley and Gorbett ). The accuracy of the proficiency test was matched with the demographics of 586 professional fire investigators. The test fire used for this survey was setup as a residential living room furnished with a polyurethane foam couch and loveseat, end tables and a coffee table. The walls and ceiling were lined with gypsum wallboard. The fire burned for approximately two minutes post-flashover.

The participants were provided a diagram of the room and photographs of the contents, walls and ceiling. An approximate 2-square foot (0.19 m ²) grid was established and the participants were asked to select the grid space that most represented their area of origin. Next, the participants were provided with depth of char measurements for all content items and depth of calcination measurements for all of the walls for the same compartment fire and were asked to re-examine the photographs and select an area of origin again. The study concluded that 73.8 % without measurable data and 77.7 % with measurable data accurately determined the area of origin. Thus, the total percentage of participants choosing the correct area increased 3.9 % with the inclusion of measurable data as part of the given. These results were found to be statistically significant using a chi square distribution yielding a p-value of 0.006.

In 2013, Andrew Cox published an article proposing a new methodology for the assessment and interpretation of compartment fire damage through the use of what he termed the origin matrix (Cox ). Essentially this work establishes a rudimentary decision matrix that uses pre-flashover and varying durations of post-flashover as the primary consideration in identifying the location and magnitude of damage within the compartment. The central theme is that the investigator can section off a room and can use the location of ventilation openings as a predictor of the location and magnitude of damage based on the location of this ventilation and the predicted airflow from these openings.

Cox discussed the importance of separating data and the interpretation of that data when discussing this new method. He contends that damage should just be viewed as data and the investigator "must resist the temptation to interpret the meaning of individual fire effects and fire patterns in isolation" (Cox ). The origin matrix provides the user a diagram of the compartment of interest, where the user is to shade in those portions of the diagram where damage is identified and then this damage is to be compared to expected damage based on the predicted damage from the ventilation openings. Cox provided a process for better interpreting the compartment fire dynamics that is still under development and has not undergone a major field test for user application.

A summary of the findings from the literature review and recommendations based on this review will be provided within this section. The literature on using fire patterns to determine an area of origin should be classified into four areas that will assist in guiding future research, including:

1. (1)

Assessing the varying Degrees of Fire Damage (DOFD) along the surfaces of the compartment and contents ( i.e. fire effects);

2. (2)

Identifying clusters and trends of damage ( i.e. fire patterns);

When lacking a systematic approach to solving complex problems, many professions have turned to decision support frameworks, tools or methods, the intent of which are to guide the decision by asking questions and helping to assess the weight or importance of variables. It is suggested from this literature review that the overall reasoning process for evaluating fire damage for determining an area of origin consists of the following seven steps (Gorbett ):

Acknowledgements

The authors would like to thank Bill Hicks for providing pictures taken during fire testing.

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Use of damage in fire investigation: a review of fire patterns analysis, research and future direction

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Fire investigators have historically relied upon damage as a means to conclude where a fire originated. This review evaluates the historical and current literature on the topic, with a specific emphasis towards the research conducted over the past 80 years related to fire patterns.

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Truncated Cone Definition

What was the last really great film you went to see at a movie theater? Going to the movies is always a great time! Of course, the experience of going to a movie at the theater isn't complete without popcorn! Most likely, you've never taken note of the shape of a popcorn tub at the theater, but here's an interesting fact! There is a mathematical name for this shape, and it's called a truncated cone.

A truncated cone is a three-dimensional object that looks like a cone with the top pointy end chopped off.

The two circular ends of a truncated cone are called the bases. We will call the radius of the smaller circular base the little radius and represent it with r, and we will call the radius of the larger circular base the big radius and represent it with R. The distance between the centers of the two bases is called the height of the truncated cone, and we represent it with h. Lastly, the shortest distance between the outer edges of the bases is called the slant height, and we represent it with s.

Do you now see that a popcorn tub has this shape? Pretty interesting, huh? Well, it's about to get even more interesting! Let's talk a bit about the volume and surface area of a truncated cone!

Truncated Cone Volume

Suppose you go to the movies, and you get a large popcorn. You can't wait to sink your teeth into the salty, buttery goodness, but before doing so, you begin to wonder just how much popcorn fits inside the large popcorn tub. I've got news for you! You're actually wondering what the volume of the popcorn tub is!

The volume of a truncated cone is the amount of space inside the truncated cone. The good news is that we have a nice formula that we can use to find the volume of a truncated cone.

Your curiosity gets the best of you, so you ask the worker at the concessions counter to see an empty large popcorn tub. When he gives it to you, you take some quick measurements and find that the big radius is 5 inches, the small radius is 4 inches, the height is 10 inches, and the slant height is 11 inches. You give the empty tub back to the concessions worker and pull out a pencil and some paper to calculate the volume of the large popcorn tub using your formula.

So, we see that the volume of the large popcorn tub is approximately 638.79 cubic inches. Wow! That's a lot of popcorn! Dig in!

Truncated Cone Surface Area

As you begin to gobble down your popcorn, you begin to have a bit of buyer's remorse. After all, you paid $8 for this large popcorn, and that's not cheap! This gets you to wondering just how much the movie theater has to pay for a popcorn tub. You have a bit more time until your movie starts, so you ask a worker how much these tubs cost them. The worker says that the manufacturer charges based on how much material was used to make the tub and a lid for the tub, and they charge 0.00125 cents per square inch of material used.

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volume & surface area of a truncated cone - video & lesson transcript | study.com

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Volume & Surface Area of a Truncated Cone - Video & Lesson Transcript | Study.com

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What was the last really great film you went to see at a movie theater? Going to the movies is always a great time! Of course, the experience of going to a movie at the theater isn't complete without popcorn!

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Foamed Plastics - an overview | ScienceDirect Topics

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Foamed plastics are also called cellular polymers and expanded plastics, and have played a great role in everyday life. Sponge is an open cellular polymer that is well known, but wood is the oldest form of foam. It is a naturally occurring foam of cellulose.

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Abstract

Thermal Conductivity plays a role in a wide variety of aspects of everyday life ranging from electronics to cooking and coffee making. In fact, without this fundamental concept energy, (in the form of heat) would have a hard time moving from place to place. This concept will be explored by exposing a piece of paper, tightly wrapped around a good thermal conductor, to a fire or source of heat above 250°C. Surprisingly, the paper does not burn when in contact with the good thermal conductor, however; the paper will burn if simply exposed to the fire. These findings indicate that good thermal conductors can transfer the heat generated from the fire away from the paper effectively preventing the paper from reaching its auto ignition temperature.

Introduction

The goal to be achieved in this experiment is a quantitative visualization of the powerful ability inherent to good thermal conductors in transferring heat across a gradient. In doing so, a greater understanding of thermal conductivity will be achieved and what roles it may play in everyday life.

Background

The fundamental concept which will be employed in the experiment is thermal conductivity. Thermal conductivity is a measure of a materials ability to conduct heat across a gradient (source of high temperature to low temperature) and is measured in Watts/Meter-Kelvin. For this experiment to be SUCCESSFUL and SAFE it is recommended to only use materials with thermal conductivities above 200 W/m-K.
Temperature of an average candle flame: 1100-1400 ⋅C (ideal circumstances)
Auto Ignition temperature of wood: 200-250 ⋅C

Materials

Procedure

1. If using a candle, place the candle on a stable flat surface as to not require being held

2. Obtain the desired piece of paper and cut out a 1-inch-wide strip along the length of the paper

3. Obtain the desired cylindrical rod

4. Wrap the piece of paper (tightly) around the rod and hold both extremities above the rod. Example below

5. Hold only the paper, place the portion of the paper, in direct contact with the metal, up to the flame for at most 5 seconds

6. Record your observations

Conclusion

The piece of paper wrapped around a metal cylinder should not ignite as compared to a freely held piece of paper. The black spot which will appear on the paper is not burnt paper. In fact, it is an impurity (soot) produced by incomplete combustion of the candle wick. This impurity should be able to be removed via wiping or eraser. If both potential situations are compared, the piece of paper with the cylinder is in contact with the metal cylinder and air, whereas; a freely held piece of paper is only in contact with air. Due to the contact with the metal, the paper can transfer the heat of the fire to the bar.

This effectively prevents the paper from reaching an auto-ignition temperature between 200-250 °C. The freely held piece of paper cannot transfer the heat from the fire to only the air due to the poor thermal conductivity of the air. Therefore, the freely held piece of paper will burn.

Taking it further

In this section put: Grab a paper cup or snow cone and fill it with water. Place it over a candle. The cup will not burn, but the water will eventually boil. This is due to water's high heat capacity; it can absorb a lot of heat when it rises in temperature. Once all, or enough, of the water has boiled away, the paper will burn.

For further information, visit:

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Unburnable paper! The impressive effects of high thermal conductivity materials - Thermtest Inc.

# data[].attributes.attachment_link.description
Thermal Conductivity plays a role in a wide variety of aspects of everyday life ranging from electronics to cooking and coffee making. In fact, without this fundamental concept energy, (in the form of heat) would have a hard time moving from place to place.

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Abstract

A controlled fire burner was constructed where various natural vegetation species could be used as fuel. The burner was equipped with thermocouples to measure fuel surface temperature and used as a cavity for microwaves with a laboratory quality 2-port vector network analyzer to determine electrical conductivity from S-parameters. Electrical conductivity for vegetation material flames is important for numerical prediction of flashover in high voltage power transmission faults research. Vegetation fires that burn under high voltage transmission lines reduce flashover voltage by increasing air electrical conductivity and temperature. Analyzer determined electrical conductivity ranged from 0.0058 - 0.0079 mho/m for a fire with a maximum temperature of 1240 K.

Keywords: biomass, forest fires, flashover, thermal ionization, alkalis

1. Introduction

When a weakly ionized medium is irradiated with electromagnetic energy, electrons in the medium gain a directed drift velocity in the direction opposite that of the applied electric field of the incident wave. The concentration of electrons, which can be up to 10 ¹⁸ m −3 in a vegetation fire [ 1] and ions which are in motion both contribute to the electrical conductivity of the weakly ionized fire. The contribution of the neutrals is in the energy dissipation processes in the fire, e.g., collisions with electrons. Vegetation fires are diffusion flames which are seeded with plants' omnipresent alkali nutrients, more especially potassium and sodium salts. Electrical conductivities of flames seeded with alkalis have been determined, e.g., in Olson et al. [ 2] and Schneider et al. [ 3]. According to [ 2], radio frequency measured electrical conductivities of high temperature hydrogen-oxygen flames seeded with alkalis were in the range of 0.04-0.27 mho/m.

The experiment considers a moderate intensity vegetation fire. The fuel, which is natural vegetation, contains up to 3.4% potassium on dry weight basis [ 4] of which up to 20% are ionized [ 5]. X-band microwaves were caused to propagate in the vegetation fire to determine electrical conductivity from network analyzer measured S-parameters.

2. Ionization in Vegetation Fires

Combustion of vegetative matter creates a hot environment with temperatures in excess of 1200 K. The high temperature environment thermally excites incumbent flame particles. The energized particles become electronically unstable, to the extent that they lose their outer shell electrons on collision with other flame particles, a process that occurs on selective basis determined by temperature and ionization potential. This process is called thermal ionization. Potassium and graphitic carbon ( Cn) are vegetation fire particles that are likely to produce appreciable ionization. This is due to the fact that the particles have low ionization energy and work functions of 4.34 and 4.35 eV respectively [ 6]. Thermal ionization of the excited flame species (FL*(g)) occurs by the following reaction equation:

Another process by which ionization may occur in the flame is chemi-ionisation. In chemi-ionisation, dissociation reactions provide part of the energy required for ionization since there are exothermic and the rest comes from the flame. Methyl radical is known for its contribution to flame chemi-ionisation reactions e.g., in Sorokin et al., [ 6]. CH radical reacts with oxygen atoms in the flame to produce CHO⁺, a primary ion in hydrocarbon flames and electrons according to the following reaction equation:

2.1. Electrical Conductivity of the Fire

The complex electric conductivity of the weakly ionized fire given by the equation

where the real (σ r) and imaginary (σ i) parts are:

and

Propagation constant (γ) of an electromagnetic wave traversing a weakly ionized medium such as fire is given by the relation:

The γ is a measure of the rate of electromagnetic energy loss through the attenuation index ( α f ) and wave dispersion through the refractive index (β f ). It can also be given in terms of the indices as:

When X-band microwaves illuminate weakly ionized, highly collisional atmospheric pressure flame plasma, α f andβ f are related to electron-neutral collision frequency and ionization by the expressions given by Mphale et al., [ 9] as:

and

where ω, c and υ eff are propagation cyclic frequency, speed of light and effective electron-neutral collision frequency, respectively.

By comparison, equations (4a) and (8) give:

The magnitude of the fire conductivity |σ| is given by the relation:

3. Results and Discussion

3.1. Flame Temperatures

Flames as high as 75 cm were observed during the combustion. The eucalyptus leaves fire took 5 to 7 minutes to extinguish. During combustion flame temperatures at the fuel surface were recorded online by a computer and are shown in .

The leaves' surface temperature rose rapidly to reach a maximum of 1240 K in 74 s. The first set of S-parameters (at ASL1) was logged in at 68 s after ignition of the leaves. At ASL1, the temperature of the litter surface was 1235 K and corresponded to the time when eucalyptus leaves flame filled the whole inner volume of the burner. After reaching the climax, the surface temperature dropped rapidly, though not as quickly as it rose after ignition, to ASL2, a second login point where the eucalyptus flame was observed to fill the inner hollow of the burner. ASL2 is at 153 s after ignition time. At ASL2, the leaves surface temperature was observed to be 946 K. Several s-parameter were logged in since ASL2, those selected for analysis were those logged in at ASL3 which corresponded to 269 s since ignition. Surface temperature at ASL3 was 695 K.

3.2. Electrical Conductivity of the Fire

The conductivity of the fire at X-band frequencies was observed to be temperature dependent. At the time at which the flame surface temperature was the hottest, i.e., at ASL1, the conductivity was the highest. It steadily decreased with the increase in frequency from 0.0079 - 0.0071 mhom −1 for 8 - 10 GHz range, respectively (see ). At 153 s after ignition, thus, at ASL2, the magnitude of flame conductivity decreased with increase in propagation frequency. It decreased from 0.0064 - 0.0060 mhom −1 in the frequency range. This was at temperature 946 K. The decrease was not as rapid as at ASL1 ().

At 269 s after ignition, i.e., at ASL3, the magnitude of flame conductivity also decreased with increase in propagation frequency. It decreased from 0.0060 - 0.0058 mhom −1 for the frequency range 8 - 10 GHz, respectively. This was at temperature of 695K.

The electrical conductivity values are low compared to those measured by other means because the flame temperatures were much lower than those cited in [ 2, 3]. Conductivity of flames is temperature dependent. Another possibility is that the fire may not have filled the whole combustion chamber, which could lead to microwave beam filling error. However, by visual inspection, those analyzed for propagation constant corresponded to situations where the fire filled the whole volume of the chamber.

4. Experimental Section

4.1. Network Analyzer and Burner System

Dielectric permittivity and propagation constant of the fire was determined by using a Hewlett- Packard 8577C vector network analyzer. The analyzer was connected to a 733 MHz computer for logging S-parameter data (see ). A hexagonally shaped burner with an insulated wooden casing was used for the combustion of eucalyptus leaves. Inside the burner, a thick (8 cm wide) thermally insulating material known as Fiberfrax was used to protect wood from the fire and heat.

A combustion chamber, circular in cross-section was lined with this material. Two vent holes of 25 mm diameter were drilled on each of the sides, except for the sides with horn inlets, to allow air to enter and mix with fuel during combustion. Two holes of horn dimensions were also cut out from the burner casing directly opposite to each other and wooden supports were provided to secure the horns firmly to the wooden casing. The internal diameter of the burner was lined up with Fiberfrax and was set to 50 cm. Two x-band transmit-receive horns were used in the experiment. They were connected to a network analyzer through the two-port s-parameter test set by coaxial cables. High quality mode transition adapters were used to make the connections between coaxial cables and the horns. Eucalyptus leaves combusted in the burner were of fuel load 6.92 ton/ha and were collected fifteen (15) days before the experiment so that they could to dry in a laboratory to maximize combustion efficiency during burning.

4.2. Flame Temperature Measurement

A thermocouple used to measure surface temperature in the burner. It was cut from a double braided fiberglass insulated chromel-alumel (24-G/G) thermocouple wire 50 μm in diameter. The thermocouple wire had a fiber glass shield which can withstand temperatures up to 450 °C. The type K thermocouple wires were electro-fused at one end to make perfect junction (bead). The bead was made small (∼ 0.12 mm) to minimize error in temperature readings due to heat transfer processes, e.g., radiation. The thermocouple was tested for accuracy and consistency in produced thermoelectric voltage using a hot air gun, thermometer and multimeter. The thermocouple was inserted from the bottom of the burner with the electro-fused junction left protruded 1cm above the fuel surface into the fire. The thermocouple was then connected to a PICO® Tech TC-O8 data logger and a laptop for online temperature measurement (see ).

4.3. S-Parameter Measurements

The 8577C network analyzer set is designed to sweep from 50 MHz to 40 GHz and logging in 601 S-parameter data points in each and every sweep. However, for the experiment, frequency range of interest was between 8 and 10 GHz. The data are then uploaded and analyzed by the computer. The analyzer takes 2 s to sample over one sweep, and then there is a latency of about 50 s before the next sweep can be initiated. The network analyzer was calibrated before use. The calibration method used in the experiment is the Transmit-Reflect-Line (TRL). Varadan et al. [ 7] give a full account of calibrating a network analyzer using TRL method. Several sweeps and logging of s-parameters were carried, but those in which flames filled the entire internal hollow space of the burner were chosen for s-parameter analysis. The selected logged in S-parameters were those at ASL1, ASL2 and ASL3, which were at 68,153 and 269 s since ignition.

4.4. Determination of Propagation and Dielectric Constants from S-parameters

The network analyzer measures the scattering parameters (S-parameters) from which the propagation and dielectric constants can be calculated. From the S-parameters analysis, propagation constant is related to the propagation factor (T) by the relation:

Kadaba [ 8] gives a full account of calculating T and complex dielectric permittivity from S-parameters. Generally, dielectric permittivity is given as:

Then attenuation ( α f ) and refractive (β ) coefficients are determined from (7) as they are real and the imaginary parts of propagation constant (γ). Complex dielectric permittivity ( ɛ̃ ) of the fire is then calculated from relation (14).

4.5. Determination of Flame Electrical Conductivity

The real and imaginary parts of electrical conductivity of the eucalyptus fire were measured at three different times (i.e., from ASL1 to ASL3) during combustion. They were determined from S-parameters using Equations (13) and (14).

5. Conclusions

Microwave electrical conductivity of eucalyptus fire with maximum temperature of 1240 K ranged from 0.0058 - 0.0079 mhom −1. The electrical conductivity could have been higher for very high intensity vegetation fires, as it is temperature and ionization dependent. Comparatively, the measured conductivity was far much lower than that reported for hydrogen-oxygen flames in [ 2]. Hydrogen-oxygen flames are usually at a very high temperature. When seeded with alkalis, as it was the case with the flames in [ 2], their electrical conductivity is increased. In [ 2], the alkali seeded hydrogen-oxygen flames conductivity was measured at the frequency of 20 MHz and was in the range of 0.04-0.27 mhom −1.

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Measurement of Electrical Conductivity for a Biomass Fire

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A controlled fire burner was constructed where various natural vegetation species could be used as fuel. The burner was equipped with thermocouples to measure fuel surface temperature and used as a cavity for microwaves with a laboratory quality 2-port ...

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Insulation materials and their thermal properties

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Using the right insulation in construction is critical to the environmental impact of the overall design. Thermal performance is critical as is the provenance of the material.

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interFIRE, A site dedicated to improving fire investigation worldwide.

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Fire Scene Electrical Checklist For the "Non-Electrical" Engineer, Goodnight, Kenneth M.

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South Yorkshire Fire & Rescue is highlighting the dangers of smoking, after recent figures show these are still a main cause of accidental dwelling fires.

Smoking related fires have remained at a similar level for the past few years. While accidental house fires are reducing, fires caused from cigarettes or other smoking materials still amount to around 60 incidents per year, the same as six years ago.

Firefighters are appealing to smokers to take extra care and to keep the risk of fire low, by following some basic fire safety advice:

* Never smoke in bed - it's very easy to fall asleep and allow your cigarette to set light to your bedclothes or furnishings
* Don't smoke if you're drowsy - especially if you're sitting in a comfortable chair or if you've been drinking or taking prescription drugs. Again, it's easy to fall asleep
* Don't leave a lighted cigarette, pipe or cigar unattended - they can easily overbalance and land on the carpet or other flammable material
* Make totally sure that your butts aren't still smouldering - wet them and empty your ashtray into a metal bin outside the house
* Keep lighters, matches and smoking materials out of the reach of children - you can also buy child-resistant lighters and containers for matches

Trevor Bernard, Head of Community Safety at South Yorkshire Fire & Rescue, said: "Smoking remains one of the biggest causes of accidental house fires, but nearly all of these can be avoided by following some basic some simple rules. For example, never smoke in bed, never leave a lit cigarette unattended, always ensure that cigarettes are put out properly and keep lighters and matches out of the reach of children."

For more information on ways to help you stop smoking visit www.nhs.uk/smokefree.
Smoking related accidental fires for South Yorkshire:

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Smoking still a main cause of accidental fires - South Yorkshire Fire and Rescue

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South Yorkshire Fire & Rescue is highlighting the dangers of smoking, after recent figures show these are still a main cause of accidental dwelling fires. Smoking related fires have remained at a similar level for the past few years. While accidental house fires are reducing, fires caused from cigarettes or ...

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Fire Dynamics

Fire Dynamics is the study of how chemistry, fire science, material science and the mechanical engineering disciplines of fluid mechanics and heat transfer interact to influence fire behavior. In other words, Fire Dynamics is the study of how fires start, spread and develop. But what exactly is a fire?

Defining Fire

Fire can be described in many ways - here are a few:

NFPA 921: "A rapid oxidation process, which is a chemical reaction resulting in the evolution of light and heat in varying intensities."

Webster's Dictionary: "A fire is an exothermic chemical reaction that emits heat and light"

Fire can also be explained in terms of the Fire Tetrahedron - a geometric representation of what is required for fire to exist, namely, fuel, an oxidizing agent, heat, and an uninhibited chemical reaction.

Measuring Fire

Heat Energy is a form of energy characterized by vibration of molecules and capable of initiating and supporting chemical changes and changes of state (NFPA 921). In other words, it is the energy needed to change the temperature of an object - add heat, temperature increases; remove heat, temperature decreases. Heat energy is measured in units of Joules (J), however it can also be measured in Calories (1 Calorie = 4.184 J) and BTU's (1 BTU = 1055 J).

Temperature is a measure of the degree of molecular activity of a material compared to a reference point. Temperature is measured in degrees Farenheit (melting point of ice = 32 º F, boiling point of water = 212 º F) or degrees Celsius (melting point of ice = 0 º C, boiling point of water = 100 º C).

References:
1 Klinghoffer, Max, M.D., "Triage Emergency Care Handbook," Technomic Publishing Company, Inc., Lancaster, PA, 1985.
2 Veghte, James H., Ph.D., "Physiologic Response of Fire Fighters Wearing Structural and Hazmat Protective Clothing," Second Annual Conference on Protective Clothing, Clemson University, May 1988.
3 Huck, Janice, "Evaluation of Heat Stress Imposed by Protective Clothing," First Annual Conference on Protective Clothing, Clemson University, May 1987.
4 American Society for Testing and Materials, ASTM C1055, Standard Guide for Heated Systems Surface Conditions That Produce Contact Burn Injuries, 4:6, ASTM West Conshohocken, PA, 1997.
5 Bynum Jr., D. Dr., Petri, V. J., et. Al.; Domestic Hot water Scald Burn Lawsuits - The Who, What, When, Why, Where How; Annual ASPE Meeting; Indianapolis, Indiana, October 25-28, 1998.
6 Shugar, G.J., Shugar, R.A., Lawrence, B., "Chemical Technicians' Ready Reference Handbook," McGraw-Hill Book Company, New York, 1973.
7 Krasny, John F., Sello, Stephen B., "Fibers and Textiles, Fire Protection Handbook," 16th Edition, 1986. NFPA, pp.5-27.
8 Fang, J.B., and Breese, J.N., "Fire Development in Residential Basement Rooms," National Bureau of Standards (currently NIST), NBSIR 80-2120, Gaithersburg, MD, 1980.

Heat Release Rate (HRR) is the rate at which fire releases energy - this is also known as power. HRR is measured in units of Watts (W), which is an International System unit equal to one Joule per second. Depending on the size of the fire, HRR is also measured in Kilowatts (equal to 1,000 Watts) or Megawatts (equal 1,000,000 Watts).

Heat Flux is the rate of heat energy transferred per surface unit area - kW/m ².

One candle vs. ten candles - same flame temperature but 10 times the heat release rate!

Heat Transfer

Heat transfer is a major factor in the ignition, growth, spread, decay and extinction of a fire. It is important to note that heat is always transferred from the hotter object to the cooler object - heat energy transferred to and object increases the object's temperature, and heat energy transferred from and object decreases the object's temperature.
CONDUCTION
Conduction is heat transfer within solids or between contacting solids.

The governing equation for heat transfer by conduction is:

Where T is temperature (in Kelvin), A is the exposure area (meters squared), L is the depth of the solid (meters), and k is a constant that unique for different materials know as the thermal conductivity and has units of (Watts/meters*Kelvin).

Thermal Conductivity of Common Materials

Convection is heat transfer by the movement of liquids or gasses.

The governing equation for heat transfer by convection is:

Where T is temperature (in Kelvin), A is the area of exposure (in meters squared), and h is a constant that is unique for different materials known as the convective heat transfer coefficient, with units of W/m ²*K. These values are found empirically, or, by experiment. For free convection, values usually range between 5 and 25. But for forced convection, values can range anywhere from 10 to 500.
RADIATION
Radiation is heat transfer by electromagnetic waves.

The governing equation for heat transfer by radiation is:

Where T is temperature (in Kelvin), A is the area of exposure (in meters squared), α is the thermal diffusivity (a measure of how quickly a material will adjust it's temperature to the surroundings, in meters squared per second) and ε is the emissivity (a measure of the ability of a materials surface to emit energy by radiation).

Fire Phenomena

Fire Development is a function of many factors including: fuel properties, fuel quantity, ventilation (natural or mechanical), compartment geometry (volume and ceiling height), location of fire, and ambient conditions (temperature, wind, etc).

Traditional Fire Development
The Traditional Fire Development curve shows the time history of a fuel limited fire. In other words, the fire growth is not limited by a lack of oxygen. As more fuel becomes involved in the fire, the energy level continues to increase until all of the fuel available is burning (fully developed). Then as the fuel is burned away, the energy level begins to decay. The key is that oxygen is available to mix with the heated gases (fuel) to enable the completion of the fire triangle and the generation of energy.

Watch
Windows: Traditional Fire Development in a Compartment Fire
Mac: Traditional Fire Development in a Compartment Fire

Fire Behavior in a Structure
The Fire Behavior in a Structure curve demonstrates the time history of a ventilation limited fire. In this case the fire starts in a structure which has the doors and windows closed. Early in the fire growth stage there is adequate oxygen to mix with the heated gases, which results in flaming combustion. As the oxygen level within the structure is depleted, the fire decays, the heat release from the fire decreases and as a result the temperature decreases. When a vent is opened, such as when the fire department enters a door, oxygen is introduced. The oxygen mixes with the heated gases in the structure and the energy level begins to increase. This change in ventilation can result in a rapid increase in fire growth potentially leading to a flashover (fully developed compartment fire) condition.

Watch

Windows: Fire Behavior in a Structure (Ventilation limited)
Mac: Fire Behavior in a Structure (Ventilation limited)

Flashover is the transition phase in the development of a contained fire in which surfaces exposed to the thermal radiation, from fire gases in excess of 600° C, reach ignition temperature more or less simultaneously and fire spreads rapidly through the space. This is the most dangerous stage of fire development.

Videos:
Compartment Fire Flashover Flashover Compilation
Reports:
Backdraft Phenomena Fatal Training Fires

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Fire Dynamics is the study of how chemistry, fire science, material science and the mechanical engineering disciplines of fluid mechanics and heat transfer interact to influence fire behavior. In other words, Fire Dynamics is the study of how fires start, spread and develop. But what exactly is a fire?

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Previous articles have addressed building factors, smoke, air track, heat, and flame (B-SAHF) as critical fire behavior indicators. Understanding the indicators is important, but more important is the ability to integrate these factors in the process of reading the fire as part of size-up and dynamic risk assessment. This is the first of two articles focused on fire behavior indicators and the stages of fire development.

Compartment Fire Development

Part of the process of reading the fire involves recognizing the stages of fire development that are involved. Remember that fire conditions can vary considerably throughout the building with one compartment containing a fully developed fire, an adjacent compartment in the growth stage, and still other compartments yet uninvolved. Recognizing the stages of fire development and likely progression through this process allows firefighters to predict what will happen next (if action is not taken), potential changes due to unplanned ventilation (such as failure of a window), and the likely effect of tactical action.

Compartment fire development can be described as being comprised of four stages: incipient, growth, fully developed and decay (see Figure 1). Flashover is not a stage of development, but simply a rapid transition between the growth and fully developed stages. (see Figures 1 and 2.)

Review of Fire Behavior Indicators

Firefighters can easily observe some of the B-SAHF indicators. However, fire behavior indicators encompass a wide range of factors that firefighters may see, hear, or feel. Some factors are relatively unchanging (i.e. building construction) and others are quite dynamic, changing as the fire develops (i.e. smoke conditions and flames).

Building: Unlike the other fire behavior factors, the building and its contents are present prior to ignition and can be examined during the preplanning process. While many common types of buildings and occupancies (such as single family dwellings) are not the focus of a formal preplan program, firefighters can examine common features and their influence on fire behavior. This pre-fire assessment of likely fire development and spread should be compared with actual fire behavior encountered during emergency incidents to improve skills in reading building factors.

Smoke and Air Track: Smoke conditions and the pattern of smoke and air movement are two of the most important indicators of fire behavior. The location and appearance of smoke can provide valuable cues related to the location of the fire, its burning regime (fuel or ventilation controlled) and the stage of fire in various areas of the building. It is critical that firefighters begin their assessment of smoke and air track indicators from outside the building, but continue this process on an ongoing basis from both the interior and exterior of the structure.

Heat: While heat cannot be observed directly, observation of the effect of heat on air track (i.e., velocity of smoke discharge), the building or exposures, and sensation of changes in temperature can be significant fire behavior indicators. It is important to remember that our personal protective equipment provides significant insulation and slows the transfer of heat and resulting sensation of changes in temperature.

Flame: Flaming combustion is often the most obvious or visible indicator observed by firefighters. However, do not get so focused on visible flames that you miss more important, but subtle building, smoke, air track, and heat indicators. Flame indicators such as location, volume, color, etc. are important, but need to be integrated into the B-SAHF framework to provide a more complete picture.

Figure 3 integrates the concept maps presented in previous articles and outlines some of the major interrelationships between the B-SHAF fire behavior indicators. (Click Figure 3 for a larger view of the concept map.)

Incipient Stage

Going back to the basics of fire behavior, ignition requires heat, fuel, and oxygen. Once combustion begins, development of an incipient fire is largely dependent on the characteristics and configuration of the fuel involved (fuel controlled fire). Air in the compartment provides adequate oxygen to continue fire development. During this initial phase of fire development, radiant heat warms adjacent fuel and continues the process of pyrolysis. A plume of hot gases and flame rises from the fire and mixes with the cooler air within the room. This transfer of energy begins to increase the overall temperature in the room. As this plume reaches the ceiling, hot gases begin to spread horizontally across the ceiling. Transition beyond the incipient stage is difficult to define in precise terms. However, as flames near the ceiling, the layer of hot gases becomes more clearly defined and increases in volume, the fire has moved beyond its incipient phase and (given adequate oxygen) will continue to grow more quickly.

Depending on the size of the compartment and ventilation profile, there may only be a limited indication (or no indication at all) from the exterior of the building that an incipient stage fire is burning within. Incipient stage indicators are listed in Table 1.

Consider the following situation and how critical fire behavior indicators would present. Use the B-SAHF model to help you frame your answers.

You have responded to a fire in a one-story single family dwelling of wood-frame construction. An incipient fire is burning a bedroom on the Alpha/Bravo corner of the structure. The fire is limited to a plastic trash can containing waste paper which is located next to the bed.

1. What conditions would you expect to see from the exterior of the structure?

2. What indicators may be visible from the front door as you make entry?

3. What might you observe traveling through the living room and down the hallway?

4. What conditions would you find in the bedroom?

It is essential to think about what you are likely to find inside when observing fire behavior indicators from the exterior and performing a risk assessment. After making entry, consider if conditions are different than you anticipated.

5. Why might this be the case?

6. What differences in conditions would be cause for concern?

Growth Stage

If there is adequate oxygen within the compartment additional fuel will become involved and the heat release rate from the fire will increase. While considerably more complex, gas temperatures within the compartment may be described as existing in two layers: A hot layer extending down from the ceiling and a cooler layer down towards the floor. Convection resulting from plume and ceiling jet along with radiant heat from the fire and hot particulates in the smoke increases the temperature of the compartment linings and other items in the compartment.

As gases within the compartment are heated they expand and when confined by the compartment, they increase in pressure. Higher pressure in this layer causes it to push down within the compartment and out through openings. The pressure of the cool gas layer is lower, resulting in inward movement of air from outside the compartment. At the point where these two layers meet, as the hot gases exit through an opening, the pressure is neutral. The interface of the hot and cool gas layers at an opening is commonly referred to as the neutral plane.

The fire can continue to grow through flame spread or by ignition of other fuel within the compartment. As flames in the plume reach the ceiling they will bend and begin to extend horizontally. Pyrolysis products and flammable byproducts of incomplete combustion in the hot gas layer will ignite and continue this horizontal extension across the ceiling. As the fire moves further into the growth stage, the dominant heat transfer mechanism within the fire compartment shifts from convection to radiation. Radiant heat transfer increases heat flux (transfer of thermal energy) at floor level. Growth stage indicators are listed in Table 2.

Returning to the scenario of the residential fire, consider the following situation and how critical fire behavior indicators would present. Use the B-SAHF model to help you frame your answers.

You have responded to a fire in a one-story single family dwelling of wood-frame construction. A growth stage fire is burning a bedroom on the Alpha/Bravo corner of the structure. The fire involves a plastic trash can, the bed, and night stand.

7. What conditions would you expect to see from the exterior of the structure?

8. What indicators may be visible from the front door as you make entry?

9. What indicators would you anticipate observing as you traveled through the living room and down the hallway to the bedroom where the fire is located?

10. What conditions would you find in the bedroom?

As the fire moves through the growth stage, the speed at which conditions change increases rapidly. After making entry, consider if conditions are different than you anticipated?

11. Why might this be the case?

12. What differences in conditions would be cause for concern?

Flashover: Transition to a Fully Developed Fire

Flashover is the sudden transition from a growth stage to fully developed fire. When flashover occurs, there is a rapid transition to a state of total surface involvement of all combustible material within the compartment. Conditions for flashover are defined in a variety of different ways. In general, ceiling temperature in the compartment must reach 500 to 600 C (932 to 1,112 F) or the heat flux (a measure of heat transfer) to the floor of the compartment must reach 15-20 kW/m2 (79.25 Btu/min/ft2)-105.67 Btu/min/ft2). When flashover occurs, burning gases will push out openings in the compartment (such as a door leading to another room) at a substantial velocity.

Recognizing flashover and understanding the mechanisms that cause this extreme fire behavior phenomenon is important. However, the ability to recognize key indicators and predict the probability of flashover is even more important. Indicators of potential or impending flashover are listed in Table 3.

It is important to remember that flashover does not always occur. There must be sufficient fuel and oxygen for the fire to reach flashover. If the initial object that is ignited does not contain sufficient energy (heat of combustion) and does not release it quickly enough (heat release rate), flashover will not occur (e.g., small trash can burning in the middle of a large room). Likewise, if the fire sufficiently depletes the available oxygen, heat release rate will drop and the fire in the compartment will not reach flashover (e.g., small room with sealed windows and the door closed).

Part two of FBI and Fire Development series will examine indicators related to the fully developed and ventilation controlled decay stages of fire development along with a review of ventilation-induced extreme fire behavior.

The fifth edition of the International Fire Service Training Association (IFSTA) Essentials of Firefighting includes an expanded chapter on fire behavior that provides simple, but solid explanation of the fundamentals of fire behavior and dynamics of compartment fire behavior. The second edition of IFSTA Fireground Support Operations (currently under development) will expand on the basic fire behavior information presented in Essentials to address the influence of ventilation on fire behavior, fire behavior indicators, and reading the fire.

Do you have a good photograph or video clip illustrating building, smoke, air track, heat, or flame indicators? If you do and would be willing to share it, please send a copy to ed.hartin@cfbt-us.com. I will be working to include photographs and video clips in future articles to provide you with an opportunity to apply your knowledge of fire behavior and skill in reading the fire.

Related Firehouse.com Articles

ED HARTIN, M.S., EFO, MIFireE, CFO, a Firehouse.com Contributing Editor, is a Battalion Chief with Gresham, OR, Fire and Emergency Services. Ed has a longstanding interest in fire behavior and has traveled internationally, studying fire behavior and firefighting best practices in Sweden, the UK, and Australia. Along with Paul Grimwood (UK), Shan Raffel and John McDonough (Australia), Ed co-authored 3D Firefighting: Techniques, Tips, and Tactics. The International Association of Fire Chiefs (IAFC), at its 2006 annual conference, recognized Gresham Fire and Emergency Services compartment fire behavior training (CFBT) program as a finalist for an Award of Excellence. At the same conference, the Commission on Fire Accreditation International awarded Ed a Chief Fire Officer (CFO) designation. To read Ed's complete biography and view their archived articles, click here. You can reach Ed by e-mail at ed.hartin@cfbt-us.com.

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Fire Behavior Indicators and Fire Development - Part 1

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Previous articles have addressed building factors, smoke, air track, heat, and flame (B-SAHF) as critical fire behavior indicators. Understanding the indicators is important, but more important is the ability to integrate these factors in the process of reading the fire as part of size-up and dynamic risk assessment.

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Introduction

Examination of the physical and chemical evidence left at a fire scene may, provided that there has not been too much disturbance, provide evidence which may enable the cause of fire to be recognized, the point of ignition to be identified and the types of fuels first ignited to be established. Directional effects may be clearly evident and the causes for particular smoke staining patterns may often be deduced. The melting or discoloration of materials within the building will provide some evidence of the temperatures attained at particular locations within the fire. To some extent, fire scene patterns can assist in the recognition of the types of fire involved. Differences between slow burning fires and rapidly developing fires can normally be recognized and these may often be further categorized.
However, there is a considerable body of unsubstantiated mythology associated with the examination of fire scene patterns and some investigators make assertions about the behavior of charred wood, cracking glass and soot, which simple experimentation would have clearly shown to have been incorrect. For example, rules of thumb based on the depth of charring of wood should be treated with the deepest of suspicion. Some investigators still believe that all wood chars at a constant rate of 1/40 in min-1 (0.06 cm min-1). Simple tests demonstrate the intuitively obvious fact that the rate of charring depends on the amount of radiant heat acting on the piece of wood.

Preliminary Examination

It is a common experience for fire investigators, when first viewing a severely damaged building, to see the situation as hopeless and unlikely to yield any significant evidence. However, very considerable bodies of evidence may be recovered after even the most severe of fires.
The investigator will immediately upon arrival at the scene begin to form opinions as to the proportion of the building damaged and will be starting to try to assess which parts of the fire damage occurred during the early stages of the fire and which occurred later. Photographs taken during the fire-fighting by the brigade and by on-lookers may help in this assessment, although they are unlikely to be available during the initial stages of the investigation. Clearly, it is normal for fires to spread from low parts of the structure upwards through the building, and if there is any significant wind, it too is likely to have played its part in influencing the direction of spread. There is likely to be more severe damage on the downwind side of the seat of the fire, even to the extent that sometimes greater heat damage may be found on the downwind side of an item rather than on the side nearest the seat of the fire.
The fire-fighting, too, is likely to drive the flames away from the initial points of attack, whilst suppressing burning near to the regions of application of water. Positive pressure ventilation, a technique increasingly used by fire brigades, is also likely to result in unusual heat and smoke patterns. This technique involves the use of powerful blowers, which force fresh air into the building, displacing smoke. Some increased burning at high levels in regions remote from the seat of the fire may occur.

High-level investigations

At some stage in the investigation, it will be necessary to decide how much importance to attribute to evidence at a high level in the fire-damaged building. Although it is unlikely that the main point of ignition will be at a high level, in cases of deliberate ignition, there may be separate ignition points at different levels in the building. In addition, it is possible for fires to spread downwards, normally by the fall of burning material from a point of ignition at a higher level.
In general, however, the most easily investigated seat of fire is likely to be at a low-level within the burnt part of the building and it is possible that any evidence that had originally been present at a high level, will have been destroyed by the flames. Point of entry evidence is also unlikely to be evident at high levels in the building. It is, however, desirable for the investigator to have a pair of binoculars available, so that evidence visible in inaccessible parts of the building may be examined safely. If the building is unsafe to enter, some examination can still be carried out from a hydraulic platform using binoculars and a camera with a telephoto lens. It is also possible that the highest parts of the building were the places where victims had been trapped by the fire, and it may be necessary to recover bodies or to examine the places where they had been found.

Exterior walls

It is normally desirable to make an exterior examination of the building and of the smoke-staining which is often apparent on the walls above windows and doorways. This staining may provide evidence of forcible entry and of windows and doors which were the first to fail during the fire. The smoke-staining to the walls may indicate the direction of the wind prevailing at the time of the fire, although it should be borne in mind that the wind direction could have changed during the period that the building burned. Normal experience of bonfires and barbecues demonstrates that the direction of smoke travel is likely to change during relatively short periods of time.

Point of entry

In many deliberately ignited fires, the premises will have been forcibly entered by an intruder, and such evidence may be clearly visible to fire-fighters and subsequent investigators. If the intruder ignited the fire from within the building, it is probable that he would have started the fire at some point remote from his point of entry, in order to escape safely as the fire developed. For this reason, it is not uncommon to find significant evidence at points of forcible entry even after the fire and the fire-fighting, provided that reasonable care has been taken by the fire brigade to preserve this valuable evidence.
Work has been carried out on techniques of restoring fingerprints left on glass and other smooth materials, subsequently affected by smoke, heat and water. In addition there may be footprints on window sills, tables and other articles of furniture near to points of entry. Other evidential materials, such as glass, blood and fibers, may also have survived the fire and fire-fighting at the point of entry. In many cases of arson by intruders, far greater implicative evidence is likely to be found at the point of entry than at the point of ignition. It should also be borne in mind that many of the more experienced criminals tend to ensure a point of exit for themselves and this region is even more likely to be free from fire spread damage.

Location of Point of Ignition

Fire scene patterns are among the methods which may be used to locate the point or points of ignition. In general, these techniques depend on the assumption that where the fire has been ignited, it is likely to burn for the longest time, producing the greatest amount of damage. Although in simple fires this may be a valid assumption, in complex fires involving difficult fire-fighting, unequal distribution of fuels or variable ventilation throughout the building, then fire scene patterns can produce misleading evidence for fire seat location and more reliable and impartial techniques should be used. Pattern-based techniques which have been commonly used include the following.
Seeking the region of maximum damage within the building Although this technique may be fairly reliable in the case of small fires, in large fires the maximum damage can be very much influenced by ventilation, the available fuel, and the fire-fighting techniques used.
Depth of charring to wood The rate of charring of wood will depend on the type of wood involved and the amount of radiant heat flux to which it has been subjected. The greater the heat flux the more rapid the rate of charring. This effect can be used to establish where the greatest heat has been involved, by comparing charred wood in different parts of the building. However, in all fires there is likely to be a considerable thermal gradient, with higher temperatures being attained at high levels within rooms. For this reason, the most meaningful comparison will normally be made at a low level where differences in temperature are more significant. The depth of charring does not provide any absolute measurement of the time for which the timber in question had been subjected to heat.
Spalling of plaster When plaster is subjected to heat it may spall from the underlying brickwork of the building (Fig. 1), providing some evidence which can be used in fire seat location. However, the sudden cooling effect due to fire-fighting water jets may also spall plaster from brickwork, although in this case there is unlikely to be any smoke deposition on the surface of the bricks.
Distortion to glass and plastic Many plastics soften at temperatures of 130-400°C. The manner of their distortion can give indications as to the direction and magnitude of the heat acting on the original item.

Figure 1 Plaster spalled from a wall as a result of cooling by fire fighting jets. The direction of the spray can be seen from displaced soot on the ceiling.
Glass tends to soften at 750-900°C. Above 900°C it is sufficiently mobile to fall to a lower, cooler position.
Distortion of metalwork Structural steelwork in buildings distorts in severe fires and the degree of distortion may indicate the regions where the greatest heat had been released.
Melted metal Commonly encountered metals melt at temperatures between 326°C for lead and over 1000° C for metals such as copper and steel. Evidence of significant quantities of melted metal may indicate that very high temperatures had been achieved in certain parts of the building.
Damage to concrete floors Concrete spalls at elevated temperatures, and high temperatures at a low level within the building may be indicated by spalling to concrete floors. Unfortunately, because of the variation in quality of concrete likely to be encountered in many buildings, confusing damage may occur. Contrary to general belief, spalling to a concrete floor does not necessarily indicate that a flammable liquid had been burnt on the surface and in fact during the burning of a flammable liquid the wetted surface tends to remain cool until all of the liquid has evaporated.
Residual heat The region where the greatest burning had occurred is likely to have been heated more than any other part of the building. It has been argued that, after the fire has been extinguished, the regions where the greatest residual heat remains may represent the seats of the fire. One complicating factor is that during fire-fighting water applied to suppress the fire will not necessarily cool the whole building uniformly and so the residual hot areas may simply represent areas where less fire-fighting water was deployed.
Burning of soot Although soot deposits in different ways (to be discussed later) one indication which has been used for fire seat location purposes, is evidence that soot has been burnt from surfaces after first being deposited. This indicates an elevated temperature and an oxidizing atmosphere and may be of significance in the enquiry.
Low burning Since fires spread predominantly upwards, the lowest region of burning might reasonably be supposed to be the seat of the fire. However, burning materials can drop down and start other fires and, in addition, a well-developed fire may possibly burn through a floor, causing damage at a lower level.
Holes in the floor When there is a single hole in the floor of a building, this may well be the seat of the fire. However, there are other possible explanations, for example it might be a region of particular fuel loading, a region of particularly good ventilation, a region where the floor had been weaker than normal or a region last to be extinguished by the fire brigade. If liquid fire accelerants have been used, they may leak through joints between floorboards causing characteristic burning patterns. However, burning beneath and between floorboards can be produced by normal fire spread. This damage cannot be regarded as conclusive evidence of the use of fire accelerants unless supported by analysis information.
Funnel patterns A seat of fire may produce a characteristic funnel pattern either in smoke or heat damage in the room or building involved (Fig. 2). However, funnel patterns are not necessarily categorical evidence of seats of fire because regions of particular fuel loading or regions where burning materials have dropped can also produce similar patterns.
Characteristic structural collapse Buildings may collapse in a manner characteristic of a fire having been started in a particular region. Interpretation of such evidence should be carried out with considerable caution because widespread travel of hot air and smoke may produce conflicting effects, as also may unequal distribution of forces within the building.
Thermal direction indicators If the furniture and contents of the building have been largely left in position, then charring and heat damage to particular faces of the furniture may provide an indication of the direction of the seat of the fire. It is important that the original positions of items should be known categorically for this type of evidence to be used.

Figure 2 A characteristic funnel pattern indicating an armchair as the point of ignition. The fire had, in fact, been ignited approximately 500 mm from the chair, but had spread to it at an early stage in the fire.
Ceiling damage Particularly intense damage to one region of the ceiling may indicate a seat of fire beneath it. However, it must be recognized that a fire at a low level in a room will cause widespread and general heating to a ceiling and the damage at a high level is less likely to be diagnostic than intense damage at a low level.
When the fire-spread pattern information and the other more objective techniques of ignition point location have been employed, it is likely that the investigator will be able to define the probable seat of fire to within certain limits. It should be possible to draw a line defining the outer limits for the possible position of the point of ignition, the confidence perimeter or radius of error. Excavation within the area defined by the confidence perimeter must include the seat of the fire. It is clear, therefore, that the whole of this area must be excavated during the investigation if any physical evidence of the cause of the fire is to be found. In general terms the more rapidly the fire has developed, the larger the confidence perimeter, because a rapidly developing fire tends to produce relatively uniform damage.
If a fire started slowly, for example by smoldering, then very localized damage may be found. It is, therefore, possible by examination and comparison of the damage to form some opinion as to how rapidly the fire has developed. In a fire which has started by smoldering and burnt slowly until it was extinguished, characteristic localized deep charring may be found. The smoke-staining, characteristic of a slow-burning fire, may show evidence of nonbuoyant pyrolysis products causing staining on the horizontal upper surfaces of objects in the vicinity.
A rapidly developing fire, on the other hand, can cause relatively uniform heat damage, with smoke which is likely to be buoyant and probably more carbonaceous than that from a smoldering fire (Fig. 3). A complication may arise because a fire which started in the smoldering form may develop into a free-burning flaming fire at some stage, possibly when the ventilation is increased, causing confusing evidence. In the most extreme case, the transition from smoldering to a free-burning fire may take the form of a 'back draught'. This phenomenon occurs when flammable gaseous pyrolysis products accumulate within the building under conditions of limited ventilation. The opening of a door or window may allow the flammable gases to ignite explosively.
The reverse of this process may occur if a large fast-burning fire is imperfectly extinguished and an area of smoldering remains unnoticed by the firefighters. Under these circumstances, a smoldering fire can occur causing intense burning in one region. Such regions of burning are likely to be in inaccessible places, in the floor boards, at the base of the wall, at the sides of cupboards and under or behind furniture. Such regions of damage, which are known as 'bulls' eyes', are relatively easy to recognize.

Figure 3 Typical smoke-logging in a passageway. Hot, buoyant smoke produces staining at a high level.

Information from Smoke Staining

The appearance of deposited smoke at fire scenes can provide valuable evidence, giving information relating to the position of items, their temperature, the behavior of the fire and the direction of smoke travel. Although the composition of smoke can vary considerably, the buoyant black smoke produced in a free-burning fire tends to deposit preferentially on cold items rather than hot, and rough surfaces rather than smooth and it deposits better when flowing in a turbulent manner, rather than laminar.
The tendency for smoke to deposit on cool surfaces is often clearly apparent, resulting in effects of selective deposition related to the underlying materials beneath the surface in question. Electrical wiring, structural steelwork and even heads of nails may act as preferential areas for smoke deposition under certain circumstances (Fig. 4). Surfaces coated with soot may suffer a rise in temperature during the development of the fire and particularly if this rise in temperature is associated with increased availability of oxygen; then areas of previously deposited soot may be burnt away producing a clean area in the middle of a blackened region.
Deposits caused by smoke from smoldering fires tend to be different in appearance, consisting of sticky, tarry pyrolysates, which tend to deposit very much more evenly, although there is a pronounced tendency for the smoke to fall, lacking as it does the buoyancy of the carbonaceous smoke from a free-burning fire.

Recognition of Types of Fire

Fire scene patterns may provide evidence to indicate the type of fire involved. Fires accelerated by the use of flammable liquids may show characteristic pool burns, particularly if they are extinguished at a relatively early stage. A pool burn shows a hard-edged demarcation line, between the irregularly shaped liquid pool and the remaining unburnt floor covering. Because of the lowering of the surface tension of most commonly encountered flammable liquids when they are heated, liquid accelerant tends to be driven under the unburnt region of floor covering. After a destructive liquid fire, samples taken from this transition zone are more likely to contain recognizable accelerant residues than samples from other regions.
Although a liquid-accelerated fire may well be evidence of arson, it is possible for flammable liquids legitimately present on the premises to cause similar effects. In addition, certain synthetic carpeting mate-rials may burn in a manner which mimics the effect of a pool burn, even if no liquid accelerant had been present. For this reason, it is normally essential that samples should be analyzed to demonstrate the presence of a liquid fire accelerant

Figure 4 Smoke tends to deposit preferentially on cooler surfaces and may reveal positions of nails and joints normally hidden by the plaster..

Fires caused by smoking materials

Although smoking materials are commonly blamed for many fires, it is difficult to demonstrate that a fire has been caused in this way. Carelessly discarded smoking materials include not only discarded lighted cigarettes, but also discarded lighted matches and tapers. Although a discarded lighted cigarette can normally only initiate smoldering, a carelessly discarded lighted match or taper can start a fire which shows all the characteristics of a free-burning flaming fire from its inception. If a lighted cigarette is suspected of having caused the fire, very localized damage is likely to be found at the point of ignition. The position of this localized damage must have been within material which was capable of smoldering and which could have been ignited by a small ignition source. Bedding, soft furnishings and piles of rubbish are the materials most commonly ignited by cigarettes. Normally, smoldering can only occur in cellu-losic materials capable of forming a rigid char. Upholstery foams are not easily ignited in this way unless a cellulosic fabric is also involved. In addition, evidence that the occupants of the building had been careless with smoking materials is likely to be found, with cigarettes, spent matches or spent tapers scattered carelessly in the unburned parts of the building.

Recognition of spontaneous combustion

In most cases of spontaneous combustion, the development of heat is likely to have been slow, and the maximum temperatures are likely to be attained within the bulk of the material which has self-heated. Although there will evidently have been disruption of the material during fire-fighting, there may still be evidence that the interior of the pile of material has reached higher temperatures than the exterior. The heating will occur in a susceptible substance, such as hay, cotton, fishmeal, sawdust and coal. There is also likely to have been a background history of heating prior to the fire.
More reactive substances such as oil-soaked rags, car body filler, quick-drying paint and certain metals are likely to self-heat more rapidly and can do so in smaller quantities. With the more reactive substances, the evidence of internal heating may not be so clearly defined as in the less reactive substance, where a larger quantity must necessarily be present for ignition to occur.

Recognition of electrical fires

The fire scene pattern evidence for electrical fires is confined to the recognition that the seat of the fire is in, or associated with, an electrical appliance or system. For an electrical appliance to cause a fire it must necessarily either emit sparks or flames, or reach a temperature such that its exterior surface is hot enough to ignite materials in the vicinity. Under both of these circumstances it is to be suspected that the interior of the appliance will have been significantly hotter than its surroundings. This is normally apparent on examination, but the increasing use of beryllium in electronic components makes the examination of electronic devices which have achieved very high temperatures extremely dangerous, because of the possible risk of inhaling beryllium oxide dust. Such examinations should only be carried out under laboratory conditions, where stringent precautions can be taken against this serious danger.
Evidence of electrical arcing in a fire scene does not, in itself, provide evidence that the fire was electrical in origin, although it may be taken as evidence that the conductors in question were live at some time during or after the fire. However, an electrical appliance suspected of having caused the fire must firstly have been live and must secondly have been in the region where the fire started. For this reason, damage to the insulation of wires within or supplying the appliance is likely to result in electrical arcing, which may have caused the operation of a fuse or miniature circuit breaker. The significance of arcing within the appliance can therefore be assessed accordingly.

Recognition of fires caused by lightning

When a fire occurs in a building during an electrical storm, the suspicion may arise that it had been caused by a lightning strike. In most countries records are kept of individual lightning strikes and it is possible to establish from a meteorological department whether such a strike had occurred in a particular area, at a particular time. In addition, examination of the fire scene patterns may demonstrate damage to roofing tiles and electrical arcing effects to vertical wiring. The effects may be particularly characteristic in wires leading between telephone inputs and receivers and vertical wires to television aerials. In addition, plug sockets may have been disrupted explosively by the lightening strike and there may be particular damage to television sets. Such evidence may well survive after relatively destructive fires.

Recognition of arson

A high percentage of fires in many countries is attributed to deliberate ignition. Although it is possible to cause a serious fire by the application of a flame to a single artifact within a building, it is more common in cases of deliberate ignition for there to be several points of ignition and for liquid fire accelerants, such as petrol or paraffin to be used. The presence of extraneous liquid fire accelerants provides strong evidence that the fire has been ignited deliberately and their presence may be suspected if liquid pool burns are found or traces of unburned liquid are smelt (Fig. 5).
Multiple seats of fire must be shown to be independent of one another if found and in a large fire it may be difficult to establish whether apparently separated seats of fire were simply the result of differing firefighting effort or different amounts of fuel present in the regions of the building. If it can be conclusively demonstrated that there had been several separated seats of fire then, provided that accidental reasons for multiple seats can be excluded, then the fire can be concluded to have been deliberately ignited. Accidental reasons for multiple seats include secondary electrical faults, disturbance of burning material, interrupted critical processes, and abnormal fire spread.

Figure 5 A typical petrol vapor explosion, which caused almost complete demolition of the building, followed by a widespread and destructive fire.

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Introduction Examination of the physical and chemical evidence left at a fire scene may, provided that there has not been too much disturbance, provide evidence which may enable the cause of fire to be recognized, the point of ignition to [...]

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For information on the latest fire statistics go to Fire Statistics at the Department of Communities and Local Government. The Fire Statistics Monitorprovides the latest quarterly figures and also provides previous quarters.

Fire statistics

Department of Communities and Local Government fire statistics provide a general purpose description of all fires and false alarms attended by UK fire brigades based on information collected from fire reports. Data collected about serious reportable fires includes:

Time and date of call

Brigade or other geographical area

Type of building or vehicle

Most likely motive (accidental or malicious)

Cause of fire (chip or fat pan fires, electrical, etc.)

Source of ignition (cigarettes, cookers, etc.)

Materials (furniture, etc.)

The spread of fire (beyond room of origin, etc.)

The nature of fire casualties

Rescue information and method of extinction

The effectiveness of automatic smoke detectors

This has been developed for brigade personnel, researchers from other government departments and other non-specialist users of fire statistics to access such data.

Fire Data

A reportable fire is an event of uncontrolled burning involving flames, heat or smoke attended by a UK fire brigade. Reportable fires are classified for data collection purposes by the Department of Communities and Local Government and by fire brigades into two main categories, the more serious primary fires for which data are collected about fires individually and secondary fires for which aggregate data are collected. Limited information about chimney fires is also collected.

Primary fires are generally more serious fires occurring in one or more of the following locations, buildings, caravans or trailers, vehicles and other methods of transport (not derelict). Outdoor storage, plant, machinery, agricultural, forestry property, other outdoor structures including post boxes, tunnels, bridges, etc., any fire involving casualties or rescues, or attended by five or more appliances, would also be categorised as a primary fire.

Secondary fires are generally small fires which start in, and are confined to, outdoor locations. Typically, they are fires in grass or heathland, fires involving rubbish, fires involving street or railway furniture and fires in derelict buildings or vehicles. Aggregated basic information is collected for secondary fires, chimney fires and false fire alarms from the monthly summary provided by brigades. However, fires in secondary locations which involve casualties or rescues or which are attended by five or more appliances are reported in the same way as a primary location.

Chimney fires are those where the damage caused is restricted to the chimney involved. Brigades record only the numbers of chimney fires.

Casualty data

Casualties from fires are categorised as fatal and non-fatal casualties. A fatal fire casualty is someone whose death is attributed to a fire, even if death occurred weeks or months later. However, it is possible that, in some cases, a subsequent death is not reported. The figures for fatalities are subject to revision as death certificates are received from the Office for National Statistics (ONS) and the Scottish and Northern Ireland Registrars General, which tends to increase the numbers. Conversely, information provided by the Fire Service is forwarded to ONS, etc. for confirmation that fire was the main cause of death, which latter information leads to a decrease in the number recorded, particularly for fires involving road vehicles.

Accidental or malicious fires

Brigades determine the most likely cause of fire on the basis of the evidence available. If the certain cause of fire is not known, brigades are asked to give the cause which could be most reasonably supposed, given the evidence available. Accidental fires make up the majority of fires in buildings, while malicious fires make up the majority of fires in road vehicles in recent years. Accidental fires include those where the cause was not known or unspecified. Malicious fires include those where malicious or deliberate ignition is merely suspected, and recorded by the brigade as "doubtful".

Since 1994, the assessment of the cause of primary fires (accidental or malicious) was made by fire brigade personnel directly ticking the appropriate box on the fire report form FDR1 rather than by data input managers at the Department of Communities and Local Government making an assessment of a text description, as used previously. This changed the classification of certain types of primary fires, from accidental to malicious. The effect appeared most noticeable for building fires, where approximately 4,000 fires may have been categorised as malicious where they were previously classed as accidental.

Why collect fire data?

Fire statistics are produced to monitor the number and characteristics of fires attended by UK fire brigades, including the causes and effects of fire so that action can be taken to reduce the human and financial cost of fire. The effectiveness of such action can also be measured by fire statistics.

The Department of Communities and Local Government and local fire brigades use fire statistics in making operational decisions, policy development and in promoting public awareness about the dangers of fire.

The timely collection of fire statistics contributes to the stated aim of the Fire and Emergency Planning Directorate of the DCLG. To ensure the reduction of fire, deaths, injury damage, to ensure the safety of the public through civil protection.

Other Government Departments also use Department of Communities and Local Government fire data, for example, the Department of Trade and Industry use fire statistics to inform their research into consumer safety issues.

There are also a small number of parliamentary questions about fire each year.

Fire Statistics History

In 1978, the Fire Damage Report (FDR1) was introduced taking over from the K433 fire report form. From 1979, the fire statistical data collected by brigades was computerized in electronic format by the Home Office. The data for the years 1978 and 1980 were not complete due to industrial action. Complete fire datasets were available for analysis back to 1981. They published fire statistics going back to the mid-1940s. In 1988 and 1989, a shortened version of coding was used for type of property and for trade or business categories, reducing the amount of detail available in these years. In 1994, form FDR1 was revised involving many changes in the structure of the fire data collected by brigades, opening up the potential for electronic data interchange between brigades and the Department of Communities and Local Government which would make possible more detailed analyses of the causes and effects of fires.

What fire data was collected?

The details of each property fire and/or fire involving casualties attended by UK fire brigades were collected on detailed reports (FDR1). These reports are keyed into a database which amounts annually to about 200,000 more serious fires where data has been collected individually. Brigades also supplied monthly summary figures for small outdoor fires, chimney fires and false alarms. These are returned to the Department of Communities and Local Government on an aggregate form (FDR3).

The British Crime Survey (BCS) is a large sample survey which is mainly concerned with measuring the extent of crime against householders in England and Wales. However, on occasion, it also includes questions on recent experiences of having a fire at home. The results provide a useful supplement to the reports collected by brigades.

Customised analysis of fire data

It was possible to create customised tables and charts based on the fire statistics collected by the Department of Communities and Local Government. The information about primary fires recorded by brigades on the FDR1 was converted by the Department of Communities and Local Government into data items which make up an annual database of fire statistics (data exists in electronic format for analysis purposes from 1981 onwards). The data items are converted into analytic variables by using a statistical analysis package. On the basis of data items collected, it is possible to derive the location of fire, most likely cause, source of ignition, spread of fire, method of fire-fighting, time and day of call to brigade, risk to life, rescue information, the details of casualties and many other variables. Since 1994, FDR1 forms have been input on the basis of a systematic sample, with the following approximate sampling fractions: 1994 - 10 percent; 1995 - 40 percent; 1996 -20 percent; 1997 - 20 percent. Each fire record is weighted to agreed brigade totals, according to the brigade area and the time of year in which the fire occurs. However, all fires involving fatal and non-fatal casualties were input, making a 100% record of casualty fires. Both fire and casualty data are revised based on information received from brigades in the following year. During the year of input and initial publication, all data are regarded as provisional.

The Incident Recording System (IRS)

The present method is an electronic system called The Incident Recording System (IRS) and is a national project led by Communities and Local Government. The IRS modernises the existing fire and rescue incident data collection system by radically changing methods of data collection. With the active engagement of fire and rescue services (FRS's) and other stakeholders this project will enable the data on all incidents attended by the UK Fire and Rescue Service to be collected electronically and verified at source, improving on the timeliness and accuracy of the previous manual collection.

Fire Statistics DCLG publications

The latest statistics can be found on the DCLG website and require an Acrobat Reader to to download them. If you would like to use the DCLG website click on DCLG and you can choose the relevant statistics you require. The National Statistics Online has datasets on fire related matters that may be of use.

Categories: Miscellaneous Fire Safety Issues

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Fire Safety Statistics for the United Kingdom

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For information on the latest fire statistics go to Fire Statistics at the Department of Communities and Local Government. The Fire Statistics Monitorprovides the latest quarterly figures and also provides previous quarters. Department of Communities and Local Government fire statistics provide a general purpose description of all fires and false alarms attended by UK fire brigades based on information collected from fire reports.

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Fires behave differently. Some burn slowly and evenly; others are extremely hot, burning fiercely and quickly. Different fires have different coloured flames. Some fires start easily; others don't. Some fires produce deadly gases that could kill you if not ventilated.

The behaviour of the fire often depends on the fuel. Other factors or variables may include where the fuel is situated and how near it is to other fuels, the weather (especially wind and relative humidity), oxygen concentration and, in the case of outside fires, the shape of the terrain.

Fuel

Type: Different fuels catch fire at different temperatures. It takes a certain amount of heat energy to change any particular material into a gas (if it is not already). Then it takes more heat energy to trigger the reaction with oxygen. The amount of heat produced depends on the molecules that make up the fuel. The most flammable fuels are hydrocarbons (contain carbon and hydrogen) that recombine with oxygen quite easily to form carbon dioxide, water and other gases.

Size: How quickly a fuel catches fire and burns relates to the surface area or the size of the fuel. For example, large pieces of wood take a lot longer to absorb heat energy to ignition temperature. A twig catches fire easily because it heats up easily.

Surface area: The bigger the area of the surface of the fuel, the more oxygen molecules can collide with the surface. The more oxygen molecules that collide per second with the fuel, the faster the combustion reaction is.

You can increase the surface area of a solid by breaking it up into smaller pieces. If you chop or break up wood into small pieces, it will ignite and burn more quickly than larger pieces of wood. People often start fires with kindling (small pieces of wood) that they criss-cross to allow greater surface area and lots of oxygen getting in and around.

A powder has the largest surface area and will have the fastest reaction rate.

Heat produced: How much energy is released in the reaction and how quickly the fuel burns depends on what the fuel is made up of. Different compounds react with oxygen differently - some contain lots of heat energy while others produce a smaller amount. The reaction with the oxygen may happen very quickly or more slowly.

Amount: The amount of fuel available to burn is known as the fuel load. The bigger the fuel load, the more intense the fire will be in terms of heat energy output.

Moisture content: If the fuel isn't dry enough, it won't burn. The less moisture in the fuel, the more likely it will ignite and burn.

Oxygen availability

The amount of oxygen available will affect the rate of burning. A low concentration of oxygen will slow the burning right down.

An example of dangerous fire behaviour that can occur in a situation where there is a low concentration of oxygen is called backdraught. This is when an enclosed fire has used up most of the oxygen and is just smouldering. If there is a sudden influx of oxygen (like someone opening a door or window), the fire will immediately explode into flame.

Weather

Relative humidity: This reflects the amount of moisture in the air. If relative humidity is low, it will contribute to the drying of fuels. If it is high, fuels will absorb moisture from the air, making ignition more difficult.

Wind: This is a major factor in determining fire spread. Wind affects the rate of oxygen supply to the burning fuel (controlling combustion) and it tilts the flame forward so that unburned fuel receives energy by radiation and convection at an increased speed. Wind can also dry out the fuel.

Rainfall: This also has an effect on wetting fuels, but absorption of moisture is dependent on fuel size. Fine fuels absorb moisture more quickly than coarse fuels. Lack of rain (precipitation) is the biggest factor affecting the drying process of fuels.

Increased temperatures: These will dry out potential fuel so that there will be less preheating of fuels to reach ignition temperature.

Terrain

The terrain (shape of the land) has significant influence on wildfire behaviour. Steep slopes may increase fire speed because fuels (scrub and vegetation) are preheated ahead of the fire through convection and radiation.

Rugged terrain with narrow valleys, sharp ridges and irregular slopes affect the direction and rate of fire spread. For example, narrow valleys can funnel winds, increasing the rate of spread of a fire due to convection.

The direction a slope is facing will depend on how much sun it gets. This will affect the amount of drying the fuels get. The drier the fuel, the faster it will burn.

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Fires behave differently. Some burn slowly and evenly; others are extremely hot, burning fiercely and quickly. Different fires have different coloured flames. Some fires start easily; others don't. Some fires produce deadly gases that could kill you if not ventilated.

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We believe that the most effective firefighting technique is prevention. Learn more about fire safety at home and work - and how to avoid accidents on the road, too.

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Deliberate Fires - Scottish Fire and Rescue Service

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Welcome to the Scottish Fire and Rescue Service - Working together for a safer Scotland

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Fires, whether in the house or commercial building, are preventable. However, there are instances where accidents happen and unintentional fires ignite. Having a fire escape plan in place can save lives.

It is just as important to know what the most common causes of accidental fires are so that you're aware of their existence.

Here is a list of common reasons for fires in the workplace:

Faulty electrical system: this includes an older electrical system with poor circuit as well as loose wires, and overloaded plugs. It is part of fire code to make sure a workplace's electricity be updated.

Flammable materials: it is not uncommon to come across flammable substances and materials in the workplace, but how they are handled and stored is where mistakes are made and fires are started.

Inadequate training of staff: human error is a major cause of workplace fires. When staff are not trained properly, they are at risk of making catastrophic mistakes.

Negligence: failure to follow protocols and procedures as well as failing to update systems so they meet code is general negligence which can result in a fire.

Arson: no one likes to think about an intentional purpose of starting a fire and solving the crime should be handled by professionals.

Here is a list of common fire starters in the home:

Grease mishandling from cooking, pots and pans overheating and combustible material being too close to burners (newspaper, paper towels, oven mitts, glass).

Ignored maintenance of heating equipment. Each year you should have your furnace and air conditioning unit looked after by a professional. When your furnace fails, you are at severe risk of carbon monoxide poisoning.

Careless smoking: this is a given. No one should be smoking in or around the home and cigarettes should be completely put out and properly disposed of.

Electrical appliances should be unplugged at the end of the day or when you are out of the home. Toasters, coffee machines, irons, etc. are known causes for accidental fires.

Candles are an unfortunate common cause of accidental fires in the home. If you must light them, be sure you're in the same space when lit and blow out when you leave.

Paint, aerosol cans, gas and other flammable liquids should be kept away from heat outlets and sunlight. When these liquids reach a dangerous temperature, they can ignite.

For fire alarms, smoke and carbon monoxide detectors, contact Life Safety Consultants.

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Most Common Causes Of Fire Accidents | Life Safety

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Fires, whether in the house or commercial building, are preventable. However, there are instances where accidents happen and unintentional fires ignite. Having a fire escape plan in place can save lives. It is just as important to know what the most common causes of accidental fires are so that you're aware of their existence.

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Whilst many think that the current demands on health and safety have gone a step too far, the statistics on fires and fatalities caused by fires tell a different story; in the first 6 months of 2013 alone, there were 140 deaths in the UK ( Gov 2013), and so workplace fire safety should remain paramount for any employer: be they big or small.

In this guide we look at the 5 most common causes of fire in the workplace, in the hope that you can glean some insight into fire proofing your work premises.
1. Faulty Electrics
Faulty electrics are the biggest cause of workplace fires, loose wires, plugs that are over loaded and old equipment can all make for a potential death trap. Every workplace is legally obliged to take good care of any electric al equipment, and Portable Appliance Testing (PAT) is an absolute must. These tests, undertaken every year, will ensure that your electrical goods stay in good working order and are fit for purpose.
2. Flammable and Combustible Materials
Flammable and combustible materials represent a dangerous hazard to your employees as well as your business; whilst every workplace should place fire safety at the forefront of their risk assessments, this is particularly true of premises that hold any number of materials that are flammable or combustible. Appropriate storage, correct disposal and in-depth processes for handling these materials and or substances should be put in place.
3. Human Error
Another common reason for fires in the workplace is down to human error, accidents such as knocking liquid onto electrical equipment, burning food in the kitchen or spilling flammable or combustible liquids.

Proper staff training can avoid certain instances, and after performing some enquiries, Uksafetystore suggest that you additionally need to ensure that you have fire extinguishers at frequent points, as well as undertaking risk assessments to identify any possible causes of accidents.
4. General Negligence
Negligence can be differentiated from human error by the fact that such incidents are caused by proper procedures not being followed, or a member of staff undertaking an activity known as a potential fire hazard. Such instances are, again, easily avoided, and staff training on the dangers of certain areas within the workplace cannot be underestimated.

Common examples of negligence include stacking or partially covering electrical equipment that requires air, improperly storing flammable items (including paper) and not following proper precautions for the handling of substances.
5. Arson
Whilst many may get alarmed when they hear that arson is a common cause of workplace fires, it is indeed a relatively frequent occurrence. Factories and industrial estates are particularly prone to vandals and fires can spread quickly from unit to unit if proper fire control features aren't installed.

If suitable, work places should fit fireproof shutters and a water sprinkler system to protect their property as far as possible; and deterrents such as CCTV and gating can all indicate to the would be intruder that your property is far from ideal for trespassing.

Featured images:

By Cormac Reynolds

Cormac Reynolds has worked for a variety of great sites in the safety area in his time. He enjoys sports and technology.

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5 Of The Most Common Causes Of Fire In The Workplace

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Whilst many think that the current demands on health and safety have gone a step too far, the statistics on fires and fatalities caused by fires tell a different story; in the first 6 months of 2013 alone, there were 140 deaths in the UK ( Gov 2013), and so workplace fire safety should remain paramount for any employer: be they big or small.

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IS IT AN ACCIDENTAL FIRE OR ARSON?

Reprinted from Chemistry in Australia Magazine April, 1989

Introduction

Damage from fire is Australia's most costly public safety problem. Losses due to fire, in life and injury, are exceeded only by those due to traffic accidents. The cost of fire damage to the Australian community has been estimated to be $600 million per year. Our own experience over recent years suggests that this may be a conservative estimate. Arson, the wilful and malicious burning of property, accounts for approximately 30 percent of this figure.

The most effective way to try and reduce this appalling cost, and to reduce the damage caused by fire, is effective fire investigation. It should then be possible to reduce the number of accidental fires by improving building codes, and by identifying and eliminating dangerous products. Arson is said to be the easiest crime to commit (even young children can do it), but the most difficult to detect and prove. It needs to be combated by finding and prosecuting those responsible.

Fire Investigation

A fire investigation is an unenviable task. The devastation, charred debris, collapsed structures, water soaked ashes, together with the smoke and stench, makes the task uninviting and seemingly impossible. In the past many investigators appear to have come to the task with inherent biases; fire brigade members have decided that all unexplained fires were due to electrical faults, whilst police and insurance investigators leaned towards "arson, by person or persons unknown".

There are different types of fires; in homes or factories, in the bush or a forest. The best investigation would use a team of trained personnel; fire brigade staff, with their experience of fires at first hand, police and insurance investigators, with their skills for determining motive and opportunities. An electrical engineer or electrician is required to investigate electrical systems. The scientist also has a most valuable role to play. The scientist should he able to arrive at a fire scene without any predetermined ideas. An analytical approach, using patient, thorough and systematic techniques should reveal critical and vital information. The knowledge of a chemist is invaluable. A chemist should understand the properties of fuels and building materials, and have an understanding of the combustion process. In addition an analytical chemist should also be able to identify in the laboratory materials found at the fire scene, even if they are only present as trace amounts.

Methodology

The basic role of an investigator at fire scene is twofold; firstly to determine the origin of the fire (the site where the fire began), and secondly to examine closely the site of origin to try and determine what it was that caused a fire to start at or around that location. An examination would typically begin by trying to gain an overall impression of the site and the fire damage; this could be done at ground level or from an elevated position. From this one might proceed to an examination of the materials present, the fuel load, and the state of the debris at various places. The search for the fire's origin should be based on elementary rules such as:

Fire tends to burn upwards and outwards (look for V-patterns along walls).

The presence of combustible materials will increase the intensity and extent of the fire; the fire will rise faster as it gets hotter (look for different temperature conditions).

The fire needs fuel and oxygen to continue.

A fire's spread will be influenced by factors such as air currents, walls and stairways. Falling burning debris and the effect of fire-fighters will also have an influence.

A knowledge of the colour and state of various materials at elevated temperatures is required to help determine the temperature of the fire in different locations. An examination is also carried out of structural deformations, char depths, smoke patterns. It is important to try and discover if the fire started at floor level, as from a cigarette butt, or at elevated level, as for a gas explosion. This summary attempts only to indicate some of the steps typically undertaken. A more detailed list can be obtained from a number of texts (see, for example, references 1,2).

These procedures are designed to locate the site of origin of the fire. Multiple sites of origin suggest a deliberately lit fire. Assuming that the site of origin has been found a thorough examination of the debris in this area is then necessary. All electrical appliances in the vicinity should be examined. The presence of any flammable liquids, trails, or spalling of concrete or intense burn-marks in the floor should be checked. No fire can commence without an ignition source. One should therefore be on the lookout for matches, lighters, sources of sparks, hot objects, chemicals, gas and electrical lines, cigarettes, fireplaces and chimneys.

A knowledge of spontaneous combustion, and its likely sources, is needed. It may be necessary to collect samples and carry out experiments in the laboratory (it is not difficult to show that loose rags with linseed oil on them cause spontaneous combustion). The collection of samples requires a chemist's knowledge of sampling procedures and the need to obtain uncontaminated materials.

Provided the investigation has been patiently and scientifically carried out, when combined with the evidence of eyewitnesses or fire officers, it may be possible at this stage to draw a conclusion about the fire. Typical causes of accidental fires are cooking accidents, overheated or short circuited electrical connections, spontaneous combustion of oils, welding sparks, burst gas lines, sparks from fireplaces, lightning, cigarette butts, left-on appliances, reacting chemicals. The list of all the possible causes is very long.

Arson

If a fire is not the result of an accident, it must have been deliberately-lit; arson. The motives to commit arson include vandalism, fraud, revenge, sabotage and pyromania. A major objective in any suspected case of arson would be to search for, locate, sample and analyse residual accelerants. Most, though certainly not all incendiary fires involve the use of an accelerant to speed the ignition and rate of spread of fire. A rapid and intense fire, inconsistent with the natural fuel loading is indicative of an accelerated fire. Such a fire is likely to be initiated at ground level, possibly in a number of sites and may produce trail marks, burn-throughs or spalling of concrete.

The accelerants most-commonly used, on account of their flammability and ready availability are petrol, kerosene, mineral turpentine and diesel. Other accelerants such as alcohols, acetone and industrial solvents are less commonly used. It might be thought (certainly many arsonists assume) that after an intense fire there will be negligible amounts of such accelerants remaining. Given our current sophistication of analytical techniques, this is not true. The amount of accelerant remaining after a fire will depend on factors such as the quantity and type of compound used, but also on the nature of material it is poured on, the elapsed time since the fire, and the severity of the fire. Chemists have been able to locate and detect trace amounts of liquid hydrocarbons in soil beneath a gutted house several months after a fire.

Detection of trace quantities of materials requires careful attention to sampling techniques and analysis. The most frequently sampled material is flooring material such as wood, carpet, soil and linoleum. Porous material is best. There is a need to take control samples in some cases, away from the area where the accelerant is suspected, but preferably of the same material as the sample.

Some investigators use "sniffers" at fire scenes. These portable detectors usually note changes in oxygen level on a semiconductor. They are not specific for liquid hydrocarbons, responding to a variety of vapours, and need to be used with caution. They can be used as a guide as to the best place from which to collect samples, for removal to, and analysis in, the chemical laboratory.

Sampling

The materials found to give the most positive analyses for accelerants are porous samples; carpet and underlay, cardboard, paper, felt, cloth and soil. At all stages, because of the sensitivity of the analysis, care must be taken to avoid contamination. In our experience unlined metal cans have been found to be the best containers.

Lined cans may have a coating which contains volatile components and should not be used. Plastic bags may allow diffusion of volatile components either into or out of the sample and are not recommended. Glass containers may be used, but the cleanliness of lids needs to be assured. Cans need to be clean and well sealed, and clearly labelled, for transport to the laboratory. At the laboratory they need to be documented and kept secure prior to analysis.
(see also: Sampling Debris at the Fire Scene)
Extraction

The methods of extraction most commonly used for fire debris samples, are distillation, solvent extraction, and headspace analysis. The distillation techniques used have included steam distillation, ethylene glycol distillation, ethanol distillation and vacuum distillation. Of these, steam distillation has been the most widely used, and is still used, particularly where reasonably large quantities of accelerant are suspected to be present. Solvent extraction is not used except in special cases. Both static and dynamic headspace analysis are now in common use, in both cases at and above room temperatures. In the former case a needle of a gas syringe is placed into a container containing fire debris, and a volume of vapour is withdrawn for analysis.

Figure 1.

Schematic diagram of Dynamic Headspace Extraction Equipment

Our own preferred method, on the basis of experience and experimentation, is for dynamic headspace extraction, as represented in Figure 1. The fire debris, in its original container is placed into an oven and heated at 150° C for approximately one hour, whilst at the same time a continuous flow of filtered nitrogen gas flushes the headspace and sweeps any volatile components through a water trap onto an absorbent. This method in effect samples 3000 times more gas than does a static headspace sample. It has the advantage that the can is always vented, so that pressure does not build up in the can. Water present will volatilise, and essentially steam distil the sample.

Absorption and Desorption

The absorbents in most common use are activated charcoal, Tenax G.C. and Porapak Q. All three used absorb accelerant components, but do not absorb water or nitrogen. Tenax is stable up to 350C and is ideal for rapid thermal desorption. It is used for most fire samples by the London Metropolitan Police Laboratories (Scotland Yard). An advantage of thermal desorption is that the material to be analysed can proceed directly from the absorbent into a gas chromatogram. One disadvantage is that when this happens the sample is used up, and the evidence is no longer present.

In the case of solvent desorption one obtains a liquid sample which can be re-analysed many times and retained as evidence. A variety of solvents have been used for desorption, but we have found carbon disulfide to be the best, because of its high desorption efficiency for the components commonly found, its low detector response and its high volatility. We use 1 mL A.R. grade carbon disulfide for extraction, and store liquid samples in a glass vial to which we add 1 mL water to prevent loss by evaporation.

Detection and Identification

Ultraviolet, infrared and nuclear magnetic resonance spectroscopy have all been used for identifying accelerant components, but by far the most widely used technique is gas liquid chromatography. It is able to separate and detect trace amounts of volatile hydrocarbons in complex mixtures. The flame ionisation detector has been widely used because of its great sensitivity for these components. The introduction of capillary columns allows for smaller samples and produces sharper peaks and greater resolution. The number of different columns now available is quite large, but we have found that a 25m. BP-1 capillary column, 0.33mm. i.d. to be widely applicable. In our laboratory we run unknown samples on a dual plotter against standard samples, so that a comparison can be made of samples run under similar conditions.

The four most commonly found accelerants (petrol, kerosene, mineral turpentine and diesel) are all highly complex mixtures of many components, in very different ratios. Most forensic laboratories feel confident in identifying these compounds on the basis of their gas chromatograms alone, even if the samples are evaporated and contaminated. Typical gas chromatograms of these four mixtures are given in Figure 2.

In order to make a positive identification it is necessary to identify a large number of the components present, and to note that their ratios are very similar to that of a standard. The use of evaporated and burnt standards may aid this comparison. To make absolutely sure of the identity of any component we have relied on gas chromatography/mass spectrometry (GC/MS). We have been fortunate to have available an AEI MS902, fitted with a Pye Unicam GC, and more recently a Hewlett Packard GC/MS, the 5970 MSD. This latter instrument contains a data library of some 42,000 compounds. It is possible to conduct searches for particular fragments, groups of fragments or molecular ions, and is particularly well suited to identify aliphatic and aromatic hydrocarbon peaks and mixtures.

We have had a number of honours students working on finding the best experimental conditions, and on identifying as many as possible of the straight and branched chain aliphatic hydrocarbons, the xylenes, tri and tetramethylbenzenes, naphthalenes and methylnaphthalenes, styrene and indanes. In the case of petrol it is also possible to detect and identify, under different conditions, the organo-lead additives. At the same time consideration has also been given to the effects of evaporating and burning accelerants. A study has also been made of likely contaminants, particularly the pyrolysis products from various plastics, carpet, wood, tiles, glues and other adhesives, lacquers, thinners, vegetable oils. We have built up a library of possible contaminants. The techniques described are capable of detecting 1 uL of accelerant. In fact it is possible to detect 0.1 uL, but we have set a minimum level of 1 uL, because of the possibility of background material which may be present. At this level one must be very careful about contamination and pyrolysis compounds, so that they are not confused with accelerant. It is necessary to clean all equipment before use and to run blanks at regular intervals to ensure that there is no contamination present.

Conclusion

Fires present a major social and economic problem. A thorough investigation of any large-scale fire, be it accidental or deliberate, is warranted. Chemists have expertise which can be used in an on-the-spot investigation, and in the analytical laboratory. This is not an area for which many scientists in Australia have been specifically trained but is an area where the chemist's skills and expertise can be of great benefit.

References

1. John D. Dehaan - Kirk's Fire Investigation (Second Edition), John Wiley. 1983.

2. Roy A. Cooke and Rodger Fl. Ide - Principles of Fire Investigation. The Institution of Fire Engineers, 1985.

Some figures discussed in this report are not available.

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T.C. Forensic: Article 3 - IS IT AN ACCIDENTAL FIRE OR ARSON?

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IS IT AN ACCIDENTAL FIRE OR ARSON? Reprinted from Chemistry in Australia Magazine April, 1989 Damage from fire is Australia's most costly public safety problem. Losses due to fire, in life and injury, are exceeded only by those due to traffic accidents.

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Fire in the forest is a destructive process. It can occur in both temperate and tropical forests. Fire can be due to the lightening or the carelessness of human beings. Nearly 90 percent of the forest fires are caused because of human beings. Also some fires start in the hot and dry weather usually in Australia.

NATURAL CAUSES OF FOREST FIRES
1) Forests fires can occur due to lightening which burns the trees but rain after it extinguishes fire causing less damage to the trees.
2) Fire needs oxygen, fuel and heat to start. Oxygen is present all around in the air, wood of the trees act as fuel and heat does not allow the fire to extinguish. At a temperature of 572 degree wood releases a gas that reacts with oxygen present in air and triggers a flame which will give heat to the surrounding woods and the fire will start growing more and more strong. This can also happen in the cold days.
3) Earthquake is also responsible for the forest fires. In 1906 earthquake in San Francisco causes fire. Other reason for fire is volcanoes and drought.
4) High temperature and low humidity (dryness) provides favorable conditions to the fire and hence it can start in forests.

MAN MADE CAUSES
1) The most common cause for the forest fire is the negligence of the people. Any source of ignition like cigarette, naked fire which when comes in contact with inflammable things causes fire.
2) Smokers sometimes drop the lighted cigarettes and matches in the forest which can easily set nearby bushes on fire and further develops into huge forest fire.
3) Tourists, picnickers sometimes throw the lighted items in the bushes around or on the ground which causes fire.
4) Locomotives that are powered by wood and coal can set on the grass and trees to fire near the railway lines with just a spark.
5) Fire lighted by cultivators to burn a patch of forest can go out of control and burning more trees than required.

Only in U.S.A. nearly 100,000 forests experience fire per year which destroys a huge amount of valuable trees.

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Fire in the forest is a destructive process. It can occur in both temperate and tropical forests. Fire can be due to the lightening or the carelessness of human beings. Nearly 90 percent of the forest fires are caused because of human beings. Also some fires start in the hot and dry weather usually in Australia.

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Wildfires are uncontrolled, rapidly spreading, and raging huge flames enhanced with wind action and firebrands that can wipe out an extensive forest or vegetation land area within minutes. Wildfires are among forces of nature that cause huge devastation to humans and environment. According to the U.S. Fire service, more than 700 wildfires occur every year, burning down approximately 7 million acres of land and destroying more than 26,000 structures. Central and local organizations work together to control tens of thousands of fires each year. The U.S. spends over $5 billion dollars to fight fires each year. That money is channeled to funding a brigade of firefighting forces including deployment of airplanes that drop water to cool the fires, drop phosphate fertilizer to slow down its spread and trucks to cut off the spread of fire.

Wildfires are also referred to as bushfires, forest fires, woodland fires, grass fires, vegetation fires, and peat fires depending on the kind of vegetation being burnt. They are unwanted, unpredictable and unplanned fires that occur in wildlands. Wildfires are so extreme that they can burn at a temperature more than 2,000 degrees Fahrenheit. That temperature is twice as hot as the surface of Venus. The flames of wildfires have the capability to reach 50 meters high. Wildfires can grow big that they change the weather patterns of a given area. They also spread fast on the ground, moving twice as fast an average human can run. With that said, it's quite difficult to stop something like that.
Here are some of the causes and effects of wildfires.
Primary Causes of Wildfires

For a fire to start, three things must be present; oxygen, heat, and fuel. Foresters call this the fire triangle. Fire will spread towards the direction where there is plenty of one of these elements. So, the only way to put out or control it is to significantly limit one of these three elements. The following are the main causes of wildfires decimating hectares of land every year:

90% of all wildfires are caused by humans. Human acts of carelessness such as leaving campfires unattended and negligent discarding of cigarette butts result in wildfire disasters every year. Accidents, deliberate acts of arson, burning of debris, and fireworks are as well other substantial causes of wildfires. Below are the detailed elaborations of the human causes of wildfires.

Smoking: A worldwide study of smoking-related fire by epidemiologists reports that smoking is the leading cause of fires and deaths globally. The report further states that these fires resulted in an estimated cost of $27.2 billion globally in 1998. The United States incurred an estimated cost of $7 billion due to wildfires in the same year. There is an uncontrolled habit of people smoking while driving, walking or biking and after finishing they would just throw away the cigarette butt without completely putting it out. Smokers at times become negligent at extinguishing the cigarettes butts after smoking.

On few occasions, cigarette buds are not properly put out before being thrown away. These individuals have no idea where those buds will end up and most start fires. This is why it's important for smokers to desist from these bad habits or ensure the buds are properly extinguished before throwing away. This kind of carelessness is what leads to wildfire disasters in many areas as the cigarette butt may end up starting a fire.

Unattended Campfires: Camping is a fascinating experience and I bet most people love camping as a way of connecting with nature and to experience some good time outdoors. However, during camping or outdoor activities people normally leave lit fires or combusting materials unattended to which can ignite wildfires. It is imperative for all lit fires and combusting materials to be totally extinguished after use to avoid wildfire disasters.

Humans sparked off about half of the 73,110 wildfires on wildlands in the United Sates in the period between 2006 and 2015. In that period, campfires contributed to one-third of the 33,700 human-instigated wildfires. Those wildfires decimated more than 1.2 million acres of land. These figures underscore the capability of campfires to start a huge wildfire. In this day and age, camping has become a big thing. Individuals, both old and young want to get out of the busy, crowded and polluted cities and its environs to spend quality time in the woods and enjoy the natural wonders. Fire is needed when temperatures fall during camping. Campfire is able to start wildfires if not properly put out.

Burning Debris: Wastes and trash are on several occasions burned to ashes as a way of reducing the accumulation of rubbish. What is left after burning the waste matter or trash is debris that burns slowly. This slowly burning debris can potentially set anything ablaze and start a wildfire because of the heat.

Burning debris is common in remote areas to get rid of junk, refuse and yard waste. Most areas permit burning of such debris. Therefore lots of people tend to think of burning debris as the first option when they pile up. But in few instances, these fires start to spread and overwhelm the individuals and leads to massive fire outbreaks. Some governments have stepped in to mitigate the situation by requiring individuals to obtain burn permits before combusting any debris.

Fireworks: Fireworks are used by humans for various reasons such as celebrations, sending signals, or illuminating areas. Birthdays, Christmas, and New Year attract wild celebrations accompanied by fireworks.

However, their explosive nature can start wildfires. Only one stray spark can start a huge wildfire and decimate hundreds of acres and lead to serious injuries. Also, due to their slow burning rate, the remaining pieces can land in unintended places thereby starting a wildfire. In 2016, fireworks started 57 fires in the state of Nebraska in the United States that culminated to $285,365 in losses. It's, therefore, critical to recognize the explosive nature and huge potential of fireworks to cause massive wildfires by blasting them at the right places.

Machinery Accidents: Machinery accidents such as the explosion of gas balloons and car crashes can ignite wildfires. The hot and explosive sparks from machinery accidents or engines can start huge forest or bush fires if the machines are operating within or adjacent to the forest or bush areas respectively.

Old outdated appliances, faulty electric outlets, extension cords, outdated wiring; space heaters can contribute to electric fires in homes when they go wrong. In fact, according to the U.S. Fire Administration, 28,600 fires are caused by electric appliances gone wrong each year. Most are accidental, but if not identified fast, they can result in widespread wildfires. Lawn mowers, car crashes, and gas balloons can also contribute to starting wildfires.

Arson: Some people may intentionally set fire to destroy land, house or any other property. This act of malicious burning of property makes up about 30% of all wildfire events. A person responsible for this heinous act is known as an arsonist. Arson specialists have substantiated that numerous fires are caused by arsonists, and that it attributes to approximately 30% of wildfire reports. As a result, arson has a dramatic effect on the risk of wildfires and can only be avoided if people desist from this kind of wicked behavior. Relevant authorities must be informed as soon as arson acts are witnessed.

Natural causes account for about 10% of all wildfires. Nevertheless, wildfires occurring as a result of natural causes vary from one region to another depending on the vegetation, weather, climate and topography. There are only two main natural causes which are lightning and volcanic eruptions.

Lightning: A fairly good number of wildfires are triggered by lightning. It a little bit difficult to agree with this fact, but researchers have found out that it's a common trigger. A lightning strike can produce a spark. Sometimes the lightening can strike power cables, trees, or rocks and any other thing and this can trigger off a fire.

The type of lightning associated with wildfires is known as hot lightning. It has less voltage currents but strikes repeatedly for longer periods. As such, fires are normally initiated by the persistent hot lightning bolts that strike rocks, trees, power cables or any other thing that might ignite a fire.

Volcanic eruption: Hot magma in the earth's crusts is usually expelled out as lava during a volcanic eruption. The hot lava then flows into nearby fields or lands to start wildfires.

Effects of Wildfires

Loss of Ecosystems and Biodiversity

Wildfires destroy the habitats and the intricate relationships of diverse flora and fauna leading to loss of ecosystems and biodiversity. Wildfires simply damage the habitable and adaptable land for specific animal and plant species. It alters or kills the plant life features which support thousands of wildlife thereby forcing the animals out of the regions or even killing them.

Smaller and rare animals including birds, squirrels, insects, rabbits, and snakes are mainly at high risks of death, whereas some plant species are burnt to ashes. Besides, wildfires can even lead to extinction for certain animals.

Wildfires can be so severe that they decimate the habits and critical relationships of plants and animals causing loss of ecosystem. Most animals are able to detect oncoming fires and migrate early. Those that can't move faster are killed. Since plant life that supports life in the area is burnt down, animals have to look for habitats elsewhere.

Forest fires such as the ones that commonly happen in dry tropical forests are a major cause of forest degradation. Whenever forest fires are experienced, thousands of acres of trees and vegetation cover are wiped out. Almost every year, forests fires are witnessed across different forest regions which persistently reduce the quality of certain forest features like soil fertility, biodiversity, and ecosystems.

We all know that living plant matter purifies the atmospheric air we depend on for respiration. They achieve this by taking in carbon dioxide, greenhouse gases, and air impurities and later give off oxygen. When plant life is exterminated by fires, the quality of air we breathe in declines and greenhouse gasses increase in the atmosphere leading to climate change and global warming. In addition, the huge clouds of smoke instigated by wildfires lead to massive air pollution.

Trees and vegetation covers act as purifiers of the air we breathe by absorbing carbon dioxide and other greenhouse gases as well as other air impurities and gives out oxygen. When they are burned down, it means more greenhouse gases increases in the atmosphere, resulting in global warming. Furthermore, huge amounts of smoke and dust are discharged into the atmosphere, causing air pollution.

Forest soils are loaded with nutrients emanating from decaying forest debris. Forest soils also consist of numerous natural features that support a plethora of life forms and organic activities. Wildfires also kill beneficial soil microorganisms that are responsible for breaking down the soil and promoting soil microbial activities. The burning of trees and vegetation cover also leaves the soil bare making it readily vulnerable to soil erosion. The high temperature caused by wildfires destroys almost the entire nutritive value of the soil.

Many have witnessed firefighters battling wildfire on TV. This could give you a rough idea of the damage wildfires can cause to the vegetation and wildlife. Wildfires devastate everything in their path including property. On top of that, local authorities spend millions of dollars to put out or control the fire. An army of firefighters is normally deployed to extinguish raging fires. Airplanes are deployed to drops huge liters of water and phosphate fertilizer from high above, not to mention the truck and logistics involved. All these costs money and the area could suffer economically moving forward.

Trees and vegetation cover acts as watershed protectors since approximately all the water comes from forest-derived water tables. Whenever they burn, the natural protection systems for water tables, streams, and rivers may be affected.

Impacts to Human Well-being and Health

Wildfires have contributed to some fatalities, especially impacting firefighters and lifesavers. The effect of smoke and dust also causes intense breathing discomfort and can worsen the health of people with allergies and respiratory disorders.

Although wildfires cause a lot of destruction and loss of lives, they have a few benefits too. The old vegetation burnt down allows new ones to spring up. There is always remarkable growth after a wildfire. Some tree species have their seeds opened and thrown to ash-enriched soils and begin to grow. For example, the Jack pine's cones open when exposed to intense heat from the fire and drop seeds into the ash-enriched soil. So, when the Jackpine dies in the fires, new ones grow.

Wildfires also promote flowering and fruiting of some plant species. This is because wood ash is one of the best fertilizers around. Wood ash contains just about every nutrient plants need including magnesium, potassium, and calcium. Ash also contain carbonates that help neutralize acidic soils to allow healthy growth of plants.

The destructive effects of wildfires can be mitigated by being responsible when handling aspects that could trigger any fire and reporting early when you witness any nature-instigated fire.

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Causes and Effects of Wildfires Wildfires are uncontrolled, rapidly spreading, and raging huge flames enhanced with wind action and firebrands that can wipe out an extensive forest or vegetation land area within minutes. Wildfires are among forces of nature that cause huge devastation to humans and environment. According to the U.S.

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http://cfbt-us.com/pdfs/cwifr_hazards_vent_controlled_fires.pdf

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Autoignition Temperature: The lowest temperature at which combustion material ignites in air without a spark of flame. (NFPA 921 3.3.13) The autoignition temperature, a material property, varies substantially with conditions; the term is sometimes presumed to refer to the temperature measured for a given material using an ASTM specified procedure.

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Fires in buildings Building Research Establishment knowledge sheets for further information.