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JSmith

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Explosives – National Center for Forensic Science

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There are two separate examinations performed in the forensic analysis of explosives: identification and/or characterization of the intact explosives and examination of explosive debris. Examiners will analyze intact explosives and residues as well as intact or fragmented device components. The ov…

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JSmith

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JSmith

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Every good thriller has at least one big explosion, right? You know, the "big boom" that always takes place right after the heart-stopping car chase, just before the hero rescues the kidnap victim who's about to die at the hand of the cleverly-written villain. Yes, that explosion.

What we don't see in our favorite thriller, though, is the collecting of evidence at explosion scenes. So let's take a moment to examine that aspect of the scenario. What should be happening in the background while the hero is saving the world?

1. Bombings/explosions are not for the Sam Spade's of the police department. Nope, these crimes should be worked by specially-trained investigators, as well as a team of experts that includes (but is not limited to) bomb disposal technicians, photographer, forensics/CSI team, medical examiner (if needed), structural engineer(s), building safety official, power company technician, additional officers to help search, etc.

2. Bombing scenes are apt to change at any moment (parts of a building may suddenly collapse, etc.), therefore, the investigator must be constantly aware of the surroundings, and he/she must thoroughly evaluate and re-evaluate before allowing evidence collection to begin.

3. As always, the scene should remain secure. A command post should be established, as well as a secure and safe location for staging collected evidence.

4. Locate and dispose of all remaining active explosives, utilizing canines, bomb robots, explosive detection chemicals, etc.

5. To avoid contamination, the team should wear protective clothing as they collect evidence and control samples. The special clothing also protects the investigator's skin from toxic material.

6. Evidence from various locations at the scene should be stored separately (do not mix).

7. Collect ALL evidence, including suspected bomb parts, batteries, wires, samples from crater, and the usual hair, fibers, blood, etc. During autopsy the medical examiner will also collect fragments removed from victims,

8. Document the scene-blast effect (are street signs leaning away from the blast scene? if so, indicate direction. trees down? cars overturned?), debris (type, amount of, and distance from the blast site), victim(s) location before and after the blast occurred.

9. Medical examiner should conduct full-body x-rays, searching for components of the bomb and other foreign material relevant to the crime.

10. And, without fail, the investigator should always...walk softly.

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Explosions: Collecting The Evidence - Lee Lofland

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Every good thriller has at least one big explosion, right? You know, the "big boom" that always takes place right after the heart-stopping car chase, just before the hero rescues the kidnap victim who's about to die at the hand of the cleverly-written villain. Yes, that explosion.

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JSmith

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Official websites use .gov
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Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Biology Biometrics Chemistry/Toxicology Environmental Fire & Explosives Firearms & Toolmarks Questioned Documents
Technology/Digital Evidence Trace Evidence Other

Fire & Explosives

ATF Detonator Database

Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF)

Database on detonators for explosive devices.

Doug Klapec
Bureau of Alcohol,
Tobacco, Firearms,
and Explosives (ATF)202.648.6130

ATF Explosive Materials Bunker

Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF)

Collection of explosive materials kept by the ATF.

Michelle Evans
Bureau of Alcohol,
Tobacco, Firearms,
and Explosives (ATF)
202.648.6143

ATF Explosives Exemplar Room

Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF)

Collection of explosive materials kept by ATF.

Michelle Evans
Bureau of Alcohol,
Tobacco, Firearms,
and Explosives (ATF)202.648.6143
Michelle.evans [at] atf.gov

Ignitable Liquids Reference Collection (ILRC)

Ignitable Liquids

National Center for Forensic Science; University of Central Florida

The database was developed by the ILRC Committee of the Technical Working Group for Fire and Explosives. It is compilation of ignitable liquids reference materials used by forensic analysts to conduct fire debris analysis. Includes the chemical composition of each reference material. It is housed at the National Center for Forensic Science at UCF, and developed by the Technical Working Group for Fire and Explosives. ILRC contains approximately 600 reference materials used by forensic analysts to conduct fire debris analysis. It consists of a comprehensive set of ignitable liquids and accompanying characterization data in accordance with the American Society for Testing and Materials E-1618 standard test methods.

Access through the URL. Online search by the following categories: SRN, Classification, HC Range, Product Use, Brand Name, Major Peaks, Predominant Ion Profile, and Keyword. To purchase physical samples, users can generate an order form off the website and then send it to the POC. No cost to access the online library; physical samples are available for purchase.

Access through the URL. Online search by the following categories: SRN, Classification, HC Range, Product Use, Brand Name, Major Peaks, Predominant Ion Profile, and Keyword. To purchase physical samples, users can generate an order form off the website and then send it to the POC. No cost to access the online library; physical samples are available for purchase.

Online library; physical samples are available for purchase.

Smokeless Powders Database (FBI)

Smokeless Powders

Federal Bureau of Investigations (FBI) -- FBI Laboratory

A searchable Microsoft Access database is used by employees to help determine what type of smokeless powder may be present in submitted casework. Actual samples of the powders are used in a comparison chemical analysis. The database contains over 800 samples.

Database can be searched through the FBI's internal network. Actual physical samples must be accessed in person. Some information is also available to the public through the TWGFEX website. Only employees of the FBI Explosives Unit have access to the entire database and reference samples.

Samples are purchased through ammunition catalogs and sporting goods stores. These samples are analyzed at the FBI lab to create digital records.

Digital records (some available online through the TWGFEX website) and physical samples.

Ronald Kelly
Federal Bureau
of Investigations,
FBI Laboratory
703.632.7641
Ronald.Kelly [at] ic.fbi.gov

Smokeless Powders Database (UCF & TWGFEX)

Smokeless Powders

National Center for Forensic Science; University of Central Florida

The database was developed by the Explosives Database Committee of the Technical Working Group for Fire and Explosives, and is designed to assist forensic explosives analysts in characterizing, classifying and comparing smokeless powder samples based on their physical and chemical properties. Approximately 100 records containing a photomicrograph of each powder, source information, physical characteristics as well as GC-MS and FTIR data identifying the chemical components.

Access through the URL; search by commercial product information, physical characteristics, and/or chemistry. No cost to access.

The FBI contributed the data for the current 100 records. Future additions will be purchased or contributed from partnerships.

Online library only.

Substrate Database

Substrates

National Center for Forensic Science; University of Central Florida

The database was developed by the ILRC Committee of the Technical Working Group for Fire and Explosives. It is a compilation of headspace GC/MS data from burned and unburned materials that are common to fire scenes. Includes the chemical composition of each reference material. Approximately 100 records of burned and unburned materials (50 total materials) common to fire scenes. Each record contains: MRN, Material Use Class, Material Use Sub-Class, Condition, Ignitable Liquid Residue Present, Product Name/Description, HC Range, Major Peaks, Predominant Ion Profile, Material Composition and Keyword.

Access through the URL; search by the following categories: MRN, Material Use Class, Material Use Sub-Class, Condition, Ignitable Liquid Residue Present, Product Name/Description, HC Range, Major Peaks, Predominant Ion Profile, Material Composition and Keyword. No cost to access.

Samples are obtained from home improvement and retail stores. ILRC Committee members contribute input for new samples.

Online library only.

Mary Williams
National Center
for Forensic Sciences - UCF
407.823.6038
mwilliam [at] mail.ucf.edu

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Official websites use .gov A.gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS A lock ( Lock A locked padlock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

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JSmith

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Evidence Packaging & Sealing Instructions

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How to properly package fire debris, explosives, and digital evidence to bring them for testing.

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JSmith

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On the morning of April 19, 1995, an ex-Army soldier and security guard named Timothy McVeigh parked a rented Ryder truck in front of the Alfred P. Murrah Federal Building in downtown Oklahoma City.

He was about to commit mass murder.

Inside the vehicle was a powerful bomb made out of a deadly cocktail of agricultural fertilizer, diesel fuel, and other chemicals. McVeigh got out, locked the door, and headed towards his getaway car. He ignited one timed fuse, then another.

At precisely 9:02 a.m., the bomb exploded.

Within moments, the surrounding area looked like a war zone. A third of the building had been reduced to rubble, with many floors flattened like pancakes. Dozens of cars were incinerated and more than 300 nearby buildings were damaged or destroyed.

The human toll was still more devastating: 168 souls lost, including 19 children, with several hundred more injured.

It was the worst act of homegrown terrorism in the nation's history.

Coming on the heels of the World Trade Center bombing in New York two years earlier, the media and many Americans immediately assumed that the attack was the handiwork of Middle Eastern terrorists.

The FBI, meanwhile, quickly arrived at the scene and began supporting rescue efforts and investigating the facts. Beneath the pile of concrete and twisted steel were clues. And the FBI was determined to find them.

It didn't take long.

On April 20, the rear axle of the Ryder truck was located, which yielded a vehicle identification number that was traced to a body shop in Junction City, Kansas.

Employees at the shop helped the FBI quickly put together a composite drawing of the man who had rented the van. Agents showed the drawing around town, and local hotel employees supplied a name: Tim McVeigh.

A quick call to the Bureau's Criminal Justice Information Services Division in West Virginia on April 21 led to an astonishing discovery: McVeigh was already in jail.

He'd been pulled over about 80 miles north of Oklahoma City by an observant Oklahoma State Trooper who noticed a missing license plate on his yellow Mercury Marquis. McVeigh had a concealed weapon and was arrested. It was just 90 minutes after the bombing.

From there, the evidence began adding up.

Agents found traces of the chemicals used in the explosion on McVeigh's clothes and a business card on which McVeigh had suspiciously scribbled, "TNT @ $5/stick, need more". They learned about McVeigh's extremist ideologies and his anger over the events at Waco two years earlier. They discovered that a friend of McVeigh's named Terry Nichols helped build the bomb and that another man-Michael Fortier-was aware of the bomb plot.

The bombing was quickly solved, but the investigation turned out to be one of the most exhaustive in FBI history.

No stone was left unturned to make sure every clue was found and all the culprits identified.

By the time it was over, the Bureau had conducted more than 28,000 interviews, followed some 43,000 investigative leads, amassed three-and-a-half tons of evidence, and reviewed nearly a billion pieces of information.

In the end, the government that McVeigh hated and hoped to topple swiftly captured him and convincingly convicted both him and his co-conspirators.

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Oklahoma City Bombing | Federal Bureau of Investigation

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The bombing of the Alfred P. Murrah Federal Building in Oklahoma City on April 19, 1995 was the deadliest act of homegrown terrorism in U.S. history, resulting in the deaths of 168 people.

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KamRon G

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In the current researches, it is observed that forensic sciences play a vital role in the field of criminal investigation. Forensic sciences has many branches which individually is involved in presenting and collecting evidences at any crime scene. Precisely investigating the explosive crime scenes, the investigators are faced with circumstances which vary from having specific resources to collect evidences and preserve them. Thus, highly sophisticated instruments are used for analysis of the evidences obtained. While some aspects, such as chemical analysis and damage effects, are discussed here. The residues are collected and from which the explosive used is known and manufacturing companies can be traced. Hence, the purpose of forensic sciences and its applications in investigations of explosive crime scenes are discussed in this article.

Keywords: Forensic Science, Explosions, Forensic Explosives, Investigators, Sophisticated Instruments.

Introduction

The forensic sciences have wide application of scientific knowledge for the law and legal system. It helps in reconstructing crime scene and on the basis of evidences obtained which gives series of events which had occurred, and it leads cases in fruitful direction of justice. Forensic sciences have many branches which includes:(Stewart, 2017)

1. Forensic chemistry

2. Forensic biology

3. Forensic physics

4. Forensic ballistics

5. Forensic psychology

6. Forensic odontology

7. Forensic anthropology

8. Wildlife Forensics

9. Cyber security

10. Forensic nursing

11. Forensic nanotechnology

And many more branches have different applications in the field of investigation.

These all branches plays specific roles in investigations of different types of crime. Generally, classify types of crimes as;

1. Accidental

2. Homicide

3. Suicide

4. Miscellaneous

What are explosives?

A substance or any compound which is reactive in nature usually light, heat, sound or pressure sensitive under which it explodes as it contains an amount of potential energy.

The objective of forensic explosives examination is the identification of any explosive present. If intact explosives particles are found, the type of explosive, producer, name of manufacturing factory can be identified. (Sodhi & Kaur, 1998)

Effects of bomb explosion (Acaemi, 1993)

1. Blast effects - the high pressure is generated. It moves like a sword cutting anything coming in its path.

2. Fragmentation - explosive in metallic container with nails form fragments.

3. Thermal effects - the hot fragments flying away and falling in any flammable material, example: fuel, gas line in many cases.

4. Vacuum effects - a vacuum or suction effect is created behind the moving blast wave. Vacuum effect is longer than blast effect. Air rushing into this vacuum which creates forces.

5. Translation effect - lifting and throwing effect.

6. Incidental effect - the blast or fragments may cause fire rupture caused damage to property and loss of many life.

Types of chemical explosives (Shen & Vieira, 2016)

1. Detonating- they are highly explosives. Example: nitroglycerine, TNT.

2. Deflagrating- they are low explosives. Example: black powder, ANFO.

Characteristics of explosives(Reno & Leary, n.d.)

1. The chemical compound or mixture of substances which is sensitive in nature.

2. Ignition is needed.

3. The rapid release of heat and large quantities of high pressure gases is observed.

4. Generally it is insoluble in water.

5. Generally, it shows no reaction to metals.

Forensic analysis of crime scene of explosives(Tourne, 2014)

An explosion is the product of chemical reactions accompanied by the sudden, rapid buildup of expanding gas pressure, producing violent physical disruption of the surrounding environment. The chemicals of forensic interest maybe in various forms, either unreacted or exploded, in bulk or trace, homemade from easily available commercial products or strictly controlled commercial or military explosives. Basically, types of explosion are classified on the basis of source or mechanism; by which the explosive pressure is produced. It includes mechanical, chemical, electrical or nuclear explosions. Examples of commonly encountered explosions include the rupture of a gas storage cylinder (mechanical), and detonation of an improvised explosive device.

The forensic expert needs to analyze and gather information on the basis of physical evidences collected at scene of crime. Many studies were conducted regarding explosive performing by performing field experiments to understand the properties of explosive, pattern of post-blast sample distribution, or potential source of evidence. There are many challenges faced by the investigating officer. The experience and knowledge on explosive residue distribution is important for comparison analysis with real samples. The origin of blast is needed to be identified and from there sample of collection is done.(Parmar & Rathod, 2012) The entire bomb site must be systematically searched with great care given to recovering any trace of a foreign substances at the site. Preliminary identification of an explosive residue using the ion mobility spectrometer can be made by noting the time it takes the explosive to move through a tube. All materials collected for the examination by the laboratory must be placed in sealed air-tight containers and labeled with all pertinent information. Debris and articles collected from different areas are to be packaged in separate air-tight containers.(Vanderheyden, Verhoeven, Vermeulen, & Bekaert, 2020) In laboratory, the debris collected at explosion scenes will be examined microscopically for unconsumed explosive particles. Recovered debris may also be thoroughly rinsed with organic solvents and analyzed by testing procedures that include color spot tests, thin-layer chromatography, high-performance liquid chromatography, and gas chromatography-mass spectrometry.(Reno & Leary, n.d.) Confirmatory identification tests may be performed on unexploded materials by either infrared spectrophotometry or x-ray diffraction. The gas chromatography is the most sensitive and reliable instrument for detecting and characterizing flammable residues.(Tourne, 2014) The vast majority of explosive cases are initiated by electric spark or chemical products. The gas chromatograph separates the hydrocarbon components and produces a chromatographic pattern characteristic of a particular petroleum product.(Griffy, 1992) By comparing select gas chromatographic peaks recovered from fire-scene debris to known flammable liquids, a forensic analyst may be able to identify the accelerant used to initiate the fire. High-performance liquid chromatography is powerful tool for analysis, it has high performance and high speed compared to traditional columns chromatography because of the forcibly pumped mobile phase(Lippincott, 1892). It applies the knowledge of biochemistry and analytical chemistry to identify, quantify and purify the individual components of mixture.(Ireland, n.d.) In HPLC, the sample is forced through a column that is packed with a stationary phase composed of irregularly or spherically shaped particles, a porous monolithic layer, or a porous membrane by a liquid at high pressure.(Huri, Ahmad, Ibrahim, & Omar, 2017)

Discussion

The most important aspects of securing the crime scene is to preserve the scene with minimal contamination and disturbance of physical evidences by barricading the crime scene at the beginning. The initial response is very expeditious and methodical. After providing medical facilities and barricading crime scene, safety procedures are to be followed. To secure and control persons at the scene is the priority. Suspects, witnesses should be isolated and after that preservation of evidences is done. To identify, establish and collection of evidences is done. After the collection of fire debris, gas sample, unknown liquids and containers. They are taken to laboratory for further investigation of them. The sophisticated instruments are used for identification of explosives used and after identification of them, the manufacturing companies and people involved can be traced. Thus, forensic sciences plays a role to identification and solving of crimes which are related with any terrorism act, accidental crimes or miscellaneous.

References

Acaemi, K. (1993). Advances in Analysis and Detection of Explosives. Advances in Analysis and Detection of Explosives. https://doi.org/10.1007/978-94-017-0639-1

Griffy, T. A. (1992). A model of explosive vapor concentration II.Advances in Analysis and Detection of Explosives. Proceedings of the Fourth International Symposium of Analysis and Detection of Explosives (Ed. J. Yinon), 503-511.

Huri, M. A. M., Ahmad, U. K., Ibrahim, R., & Omar, M. (2017). Satu ulasan pengesanan residu letupan dari sudut pandangan kimia forensik. Malaysian Journal of Analytical Sciences, 21(2), 267-282. https://doi.org/10.17576/mjas-2017-2102-01

Ireland, N. (n.d.). Analysis of Explosives and Firearms Residue Using Thermo Scientific Atlas CDS TM at Forensic Science.

Lippincott, C. D. (1892). Explosive Substances. Scientific American, 34(874supp), 13973-13974. https://doi.org/10.1038/scientificamerican10011892-13973csupp

Parmar, P., & Rathod, G. B. (2012). ijcrr, 04(10), 33-38.

Reno, J., & Leary, M. Lou. (n.d.). A GUIDEfor Explosion Bombing Explosion Bombing SCENE INVESTIGATION and. Retrieved from http://www.ojp.usdoj.gov

Shen, M., & Vieira, D. N. (2016). Forensic science: defending justice. Forensic Sciences Research, 1(1), 1-2. https://doi.org/10.1080/20961790.2016.1243083

Sodhi, G. S., & Kaur, J. (1998). Forensic Investigation of Explosions. Forensic Investigation of Explosions, 5(2). https://doi.org/10.4324/9780203483510

Stewart, L. F. (2017). Crime Scene Investigation - Explosives. Foresic Research & Criminology International Journal, 4(5), 143-144. https://doi.org/10.15406/frcij.2017.04.00127

Tourne, M. (2014). Developments in Explosives Characterization and Detection. Journal of Forensic Research, s12(01). https://doi.org/10.4172/2157-7145.s12-002

Vanderheyden, N., Verhoeven, E., Vermeulen, S., & Bekaert, B. (2020). Survival of forensic trace evidence on improvised explosive devices: perspectives on individualisation. Scientific Reports, 10(1), 1-11. https://doi.org/10.1038/s41598-020-69385-1

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Forensic science, forensic explosives and explosion investigation

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In the current researches, it is observed that forensic sciences play a vital role in the field of criminal investigation. Forensic sciences has many branches which individually is involved in presenting and collecting evidences at any crime scene. Precisely investigating the explosive crime scenes, the investigators are faced with circumstances which vary from having specific [...]

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KamRon G

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KamRon G

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An explosion occurs as the result of a chemical reaction which releases a vast amount of physical or chemical energy accompanied by light, heat and sound in a short space of time. The cause of an explosion could range from a simple accident in the home to a major terrorist incident. Either way, an intricate investigation must take place to establish the exact circumstances of the event.

The construction of a bomb can be fairly simple, some requiring just a timer or remote control to create an initial spark, which ignites the bomb and triggers a blast. The recipes for making such a bomb are readily available online. The strength of a bomb can vary greatly, some yielding little power and others causing mass destruction, depending on the chemical reactants used and the construction of the device itself.

Detonating cords are common parts of many explosive devices. These are plastic tubes filled with powdered explosive, for instance PETN (pentaerythritol tetranitrate), commonly used to link charges through the transmission of the detonation shock wave or as the explosive charge themselves. Explosive devices will often contain boosters, components which amplify and transmit the shockwave between the detonator and main charge. Many bombs require some kind of trigger to initiate the detonation, so timers or remote control devices are commonly used. These start the initial charge, which then goes on to ignite the explosive and detonate the bomb.

The Investigation
The site of an explosion must first be deemed safe before officers may proceed with their investigation. As with in fire investigations, consideration must be given to the structural integrity of buildings, dangerous materials such as glass and metal, and flammable or toxic substances. In bombing cases there is always the possibility that second devices have been placed, either bombs that did not detonate as planned or those specifically designed to harm people responding to the incident. Therefore the area should be deemed structurally safe, experts should be called in to locate any further explosives, and appropriate protective clothing should be worn. As with any crime scene, a cordon will be placed around the area to preserve evidence and control who can enter the scene. The diameter of the cordon will be dependent on the incident, as an unexploded device requires a smaller cordon as no debris is involved.

Initially the investigation will establish whether an explosion has actually occurred. Explosions will result in specific damage being caused to surrounding areas, the presence of which may indicate such an incident has taken place. Therefore investigators will search for this characteristic damage. Textiles will take on specific material when subjected to the heat caused by an explosion, with many melting and once again solidifying, displaying clubbed damage. Surfaces slightly further away, such as rooftops and stationary vehicles, are likely to collect soot deposits from materials burned during the explosion. The pressure and heat of the blast will cause specific damage to nearby surfaces, the kind of damage being specific to the material. Once confirmed, the origin of the explosion will be located. The presence and depth of specific damage or a crater may indicate the origin, or seat, of the explosion. It must then be established whether the incident was caused by maliciously placed explosives or if it was an accident, such as a gas leak. Investigators will be on the lookout for both signs of potential gas leaks and similar but also for indicators of bomb use.

Before and throughout the investigation any witnesses to the incident will be interviewed. Witness reports are useful for gathering information on any occurrences leading up to the explosion, details of the explosion itself, and anything else that may be relevant, such as the sightings of suspicious individuals.

During the investigation of an explosion scene, investigators must search far and wide for possible fragments, as much of the bomb is thrown far from the epicentre due to the heat and kinetic energy produced. Fragments may be found on rooftops, under other debris, and even embedded in other objects or victims. All fragments should be collected to ensure the bomb can be reconstructed. Such fragments may also carry fingerprints belonging to the perpetrator. Components searched for at a crime scene include detonators, tapes, wires, timers, switches, and batteries. Once all present components have been collected, experts may be able to establish what kind of explosive device was used, including its construction and how it was triggered. The type of explosive used, its construction, or specific components used may be useful in locating the bomb maker, particularly if a series of explosions have occurred over a period of time. Similarly, particular terrorist organisations may be known for using a specific type of explosive. An investigation may often be conducted into recent purchases of certain substances. Explosives are generally strictly regulated by the government, and so a flag may be raised when an individual purchases a particular chemical. However materials used in bombs are often stolen or smuggled into the country, so the components may be more difficult to trace. Furthermore, bombs can be constructed from everyday products, thus tracing the purchase of such materials to a specific individual is not a viable option.

Investigations are not limited to the scene of the explosion incident itself, but can be extended to the homes of suspects. Homes may be examined and analysed for any indication of bomb construction, including bomb fragments and explosive substances. Surfaces will be swabbed to detect the presence of minute traces of explosive residues, either using chemical indicators or to collect samples for further laboratory analysis.

Types of Explosive
Explosions may have a chemical and physical element. The first relates to the chemical energy stored in the explosive molecules which produce the heat, light, sound, and kinetic energy. A physical explosion may be the sudden release of pressure, such as in the explosion of a container of gas.

A detonation is a subsonic explosion with a speed greater than the speed of sound in that material, with a pressure wave of up to 8500 metres per second. This occurs in high explosives. Detonations tend to have a shattering effect, and a particularly condensed explosion will cause a huge crater.

Deflagration is a type of subsonic combustion which occurs slower than the speed of sound in that material, creating a pressure wave of up to 1000 metres per second or less. It is usually propagated by thermal conductivity and is common to most every day fires. Condensed explosives undergoing deflagration produce extreme heat which will melt surrounding objects.

There are two kinds of explosive: low explosive and high explosive. Low explosives are characterised by their ability to burn in the same way any other combustible material would. They exert a throwing or pushing effect when the explosion occurs, with a blast front velocity below 400ms-1. Examples of low explosives, also known as propellants, include gunpowder and nitrocellulose. High explosives are much more dangerous, having more of a shattering effect and exploding at a rate of between 100 and 8500 metres per second. They have a blast front velocity of 400ms-1, and can reach up to 19000ms-1. High explosives can be primary or secondary. Primary high explosives are very sensitive, with an example being nitroglycerine. Secondary explosives are conversely fairly insensitive, with examples including PETN and TNT.

A variety of explosives are commonly encountered, their construction and mechanisms specific to their use.

Pipe Bombs - Simple construction generally consisting of a short length of pipe with both ends capped. One end is drilled and the detonator inserted, and either high or low explosives may be used. Parts of this bomb usually survive the blast and may hold evidence such as fingerprints and manufacturer details.

Vehicle Bombs - These generally use large quantities of low explosive with a high explosive booster. The bombs are placed inside vehicles which can generally be subtly left in the target location where they will often cause great destruction. It is usually possible to at least identify the make and model of the vehicle used and potentially even its owner.

Letter & Parcel Bombs - These generally contain a small amount of high explosive packaged inside an inconspicuous letter or parcel. Such bombs often yield forensic evidence as the devices rarely cause fires and so less evidence is destroyed.

Mines - These are concealed devices containing high explosive, commonly used by the military. Mines are often hidden and detonated when touched. Much forensic evidence can often be obtained from the device.

Suicide Bombers - Suicide bombers, usually an individual wearing a vest of explosives or carrying a device, are primarily utilised by terrorist organisations. These types of bombs allow for the explosives to literally be walked into the target location and placed close enough so that maximum destruction can be caused. The identity of bombers can often be ascertained from CCTV footage and witness statements. Parts of the bomber may even be found, as the upper torso and head sometimes survive the blast and are found a distance away from the epicentre of the blast. Many terrorist organisations will publish or advertise the identity of the bomber after the event has occurred.

Detecting Explosives
Throughout the investigation various techniques may be utilised to detect explosive residues, either traces left behind by the explosive device or materials used in the production of the explosives.

The use of specially trained dogs is perhaps one of the oldest methods of detecting explosives. These canines are trained to use their exceptional sense of smell to detect and locate the presence of even the slightest traces of explosive material. They may equally be utilised at the crime scene itself to detect more explosive devices or residues, and in homes of suspects to establish whether the location bears any trace of such substances. The dogs may also be instructed to detect explosive scents on people and their clothing. You can read more about these trained dogs on the detection dogs page.

Similar to trained canines are electronic 'sniffer' devices. Explosives generally emit certain volatile components which the device can detect. The air is drawn through a filter, causing the components to collect where they can then be analysed, giving some indication as to its composition. However some explosives, such as plastic explosives, are not easily detected by these devices, therefore canines may be more useful in this respect. Detection techniques should always be used in unison rather than exclusively.

Away from the crime scene, standard analytical techniques may be used to detect and identify explosive substances. Mass spectrometry and gas chromatography are frequently used in the analysis of samples collected from the scene to identify any explosive residues.

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An explosion occurs as the result of a chemical reaction which releases a vast amount of physical or chemical energy accompanied by light, heat and sound in a short space of time. The cause of an explosion could range from a simple accident in the home to a major terrorist incident.

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General guidelines to assist fire investigators collect accelerant evidence after a fire.

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KamRon G

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The National Institute of Justice's National Center for Forensic Science at the University of Central Florida has developed a project to create a database of explosives detailed enough for law enforcement agencies to identify the manufacturer and the country where the explosive was manufactured. The explosive database operates where each type of explosive, such as TNT, C4 and nitroglycerin are chemically analyzed and the results are then compiled in the database. By knowing the type of explosive, its content, the manufacturer, and the country of origin, law enforcement agencies can narrow down the investigation. The database offers law enforcement agencies with a highly beneficial tool in bomb scene investigations.

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Explosive Database | Office of Justice Programs

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The National Institute of Justice's National Center for Forensic Science at the University of Central Florida has developed a project to create a database of explosives detailed enough for law enforcement agencies to identify the manufacturer and the country where the explosive was manufactured.

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KamRon G

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