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What are exhaust systems, and how they differ from each other?

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What are exhaust systems, and how they differ from each other?

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Can be classified into three types:

Chemical fume hoods (for corrosive acids and bases, volatile solvents, and other hazardous chemicals)

Biological safety hoods (also called clean air benches or biosafety cabinets) (for sterile work and biological protection)

Standard exhaust hoods (used in mechanical workshops, machine shops, and production areas for general ventilation)

These systems control and treat emissions, protecting personnel and the environment

Ensure compliance with strict safety and environmental regulations

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Experiment 1: Highly reactive and relatively toxic gases will be used

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Experiment 1: Highly reactive and relatively toxic gases will be used

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Exhaust system: Glove Boxes

Storage: Toxic gas cabinets

Why?

Designed for safe storage and handling of hazardous gases

Connected to exhaust system → removes leaked gases continuously

Reduces risk of exposure to laboratory personnel

Operate under negative pressure

Equipped with gas detection systems

Has automatic shut-off functions

Helps respond quickly to gas leaks

Conclusion:

Provides proper containment and ventilation

Ensures safe and controlled experiment

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Experiment 2: Sealed Environment (Glove Box)

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Experiment 2: Sealed Environment (Glove Box)

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Provides a completely enclosed and airtight workspace, isolating samples from the external environment

Manipulation is done through built-in gloves, preventing direct contact and contamination

Internal atmosphere can be controlled using inert gases (e.g., nitrogen or argon) to remove oxygen and moisture

Equipped with an airlock/antechamber system for transferring materials without exposing the main chamber

Can operate under:

Positive pressure → prevents outside air from entering, protecting sensitive samples

Negative pressure → prevents hazardous substances from escaping, protecting the user

Ensures high level of contamination control and stable experimental conditions, improving reliability of results

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Description : Biological samples such as bacteria and cells will be involved.

Exhaust system: Biosafety cabinet

Class I:
A Class I biosafety cabinet has an open front and draws air into the cabinet, which is then filtered before being exhausted, providing protection to the user and the environment but not to the sample.

Class II:
A Class II biosafety cabinet uses HEPA-filtered laminar airflow to create a sterile working area, providing protection to the user, the sample, and the environment.

Class III:
A Class III biosafety cabinet is a completely sealed, gas-tight enclosure operated with built-in gloves, providing maximum protection to the user, the sample, and the environment when handling highly hazardous materials.

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What are the potential safety hazards associated with each exhaust system

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What are the potential safety hazards associated with each exhaust system

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Toxic Gas Cabinets

Gas leaks (toxic, flammable, or corrosive gases)

Fire or explosion risk from reactive gases

High-pressure cylinder rupture or failure

Exposure during gas cylinder handling or changeover

Glove Boxes

Loss of containment due to glove puncture or seal failure

Oxygen or moisture ingress causing unwanted reactions

Pressure imbalance leading to structural damage

Cross-contamination between samples

Biosafety Cabinets (BSC)

Exposure to biological agents if airflow is disrupted

Sample contamination due to improper airflow or technique

Aerosol escape if airflow is blocked

Inadequate containment of volatile or toxic chemicals

Ductless Fume Hoods

Filter saturation leading to release of hazardous vapors

Recirculation of contaminated air into the laboratory

Ineffective filtration for incompatible or unknown chemicals

Gradual loss of filtration efficiency over time

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How can they be mitigated through proper use and maintenance?

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How can they be mitigated through proper use and maintenance?

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1. Risk assessment

identify the hazards (ie substances or conditions with the potential to cause harm)

evaluate the associated risks (ie the likelihood of that harm being realised) - The assessment must consider conditions other than the normal operating ones, ie spillage, catastrophic failure of any component within the system (ie fan), or any other condition likely to present adverse conditions. The assessment must consider the competence of those undertaking the work, and will determine the necessary levels of supervision.

2. Fume cupboard selection

The hazards presented by an experiment must be matched to the capabilities of the system, therefore it is essential that performance data (ie containment test results) are considered as part of the risk assessment. In laboratories containing a number of fume cupboards it is likely that some will perform better than others. In such circumstances efforts must be made to use the most effective cupboards with the most hazardous experiments

The physical integrity of the system must be considered, ie its ability to withstand corrosive acid fumes or its fire resistance when using highly flammable substances. It is important to consider all parts of the system (ie ducting, fan-casing etc), and not just the enclosure.

3. Pre-use operation check: Before the start of every day during which the exhaust systems are to be used, the operator must complete a simple checklist to confirm the following basic functions of the system: on/off controls, the sash mechanism, the reading of a performance indicator (if present) and the internal lights. This would ensure that any defects would be discovered prior to any experimentation for repairs.

4.Maintenance: Control measures used to prevent exposure to hazardous substances are to be maintained in an efficient state, and must be thoroughly examined and tested every fourteen months and the frequency of testing may be increased in accordance with the risk assessment of the effects of system failure. This reduces the probability of system failures that would result in significantly high risk of exposure, which can be further decreased with additional measures like post-performance maintenance testing.

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Scenario 2: Selection of Appropriate Exhaust Systems

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Scenario 2: Selection of Appropriate Exhaust Systems

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A chemical manufacturing facility has a variety of exhaust systems available in their laboratory, including toxic gas cabinets, glove boxes, biosafety cabinets, and ductless fume hoods. One of the employees is planning to conduct four individual experiments that involve the following requirements:

Experiment 1: Highly reactive and relatively toxic gases will be used.

Experiment 2: A sealed environment is necessary to protect the samples from contamination.

Experiment 3: Biological samples such as bacteria and cells will be involved.

Experiment 4: Volatile and hazardous chemicals will be used.

Discussion questions:

1. What are exhaust systems, and how do they differ from each other?

2. What are the potential safety hazards associated with each exhaust system, and how can they be mitigated through proper use and maintenance?

3. Which exhaust system is best to use for each experiment? Why?

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Reason:

1. Protects the user

Prevents inhalation of aerosols containing bacteria or pathogens

Uses HEPA-filtered airflow to trap harmful particles

2. Protects the sample

Maintains a sterile environment

Prevents contamination from dust, air, or the operator

3. Prevents environmental contamination

Stops microorganisms from escaping into the lab

Reduces risk of spreading infection

4. Controls airflow safely

Ensure air flows is in a specific direction (laminar flow + filtration)

Ensures contaminants are contained and removed

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Toxic gas cabinets: are high-integrity enclosures specifically engineered to house and manage compressed cylinders of gases that are highly reactive, corrosive, or toxic. Because these gases pose a significant immediate danger to life and health (IDLH), these cabinets utilize "total containment" engineering rather than simple ventilation.

Safety features

Continuous Negative Pressure: The cabinet is constantly exhausted to ensure the internal pressure remains lower than the surrounding laboratory. If a leak occurs, the air is pulled into the cabinet and through a dedicated duct system rather than escaping into the room.

Leak Detection Sensors: These cabinets are equipped with specialized sensors calibrated to detect specific gas concentrations at levels well below their hazardous thresholds.

Automated Gas Shut-off Valves: A critical safety feature is the integration of automated valves that can physically close the cylinder's flow. These are programmed to trigger instantly if the sensors detect a leak or if the system detects a loss of exhaust airflow.

Fire-Rated Construction: Most professional-grade cabinets are built from heavy-gauge, fire-resistant steel to protect the cylinders from external heat sources and contain potential internal reactions.

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Ducted fume hood chose.

total remove the hazardous away.

Have deducted hood.

Maintain a consistent speed of air entering the hood.

Ensure bursts of vapor captured.

Prevent the buildup of explosive concentrations of vapors within the cabinet.

Constructed with materials that can withstand chemical fires.

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Biosafety cabinets: are among the most critical pieces of equipment in microbiology and clinical laboratories. Unlike standard fume hoods, which only protect the user, a BSC is designed to provide "triple protection": for the personnel, the environment, and the product (the sample itself).

The core of a BSC’s functionality lies in its use of High-Efficiency Particulate Air (HEPA) filters and Laminar Airflow.

Laminar Flow: Air is pushed through a HEPA filter in a single, unidirectional stream at a constant velocity. This creates a "curtain" of clean air that prevents room contaminants from entering the work zone and prevents aerosols generated by the work from escaping.

HEPA Filtration: These filters are designed to capture 99.97% of particles that are 0.3 μm in diameter. Since most bacteria and viruses travel on larger droplets or dust particles, they are effectively trapped within the filter medium.

The "Air Curtain": At the front opening (the sash), room air is pulled into a front grille. This inward airflow ensures that no biological agents escape toward the researcher.

Classification

Class 1: Personnel & environment only

Low-to-moderate risk agents where product contamination isn't a concern.

Class 2: Personnel, Environment, and Product.

Gold standard for most microbiology labs capable of handling level 1,2 and 3 agents.

Class 3: Total Containment (Glove Box style).

Highly infectious "Level 4" pathogens (e.g., Ebola, Anthrax).

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A safety setup used with a glove box (sealed enclosure) to safely remove contaminated air, vapours, or particles generated inside the box, especially when working with hazardous chemicals, biological or radioactive materials.

Contains built-in gloves that allow the user to handle dangerous substances without direct exposure, while maintaining a controlled environment (e.g., sterile, inert gas like nitrogen, or negative pressure).

Key Components:

Air inlet: brings in clean air or inert gas

HEPA filters: trap fine particles (e.g., microbes, powders)

Activated carbon filters: remove chemical vapours and gases

Exhaust fan/blower: pulls contaminated air out

Ducting system: directs air to safe discharge (outside building)

Pressure control system: maintains negative pressure (prevents leaks)

Types of Exhaust Systems

1. Single-pass exhaust

Air enters → passes through glove box → filtered → exhausted outside

Used for toxic or hazardous materials

2. Recirculating system

Air is filtered and returned to the glove box

Used when maintaining inert atmosphere (e.g., oxygen/moisture-sensitive work)

3. Negative pressure system

Internal pressure lower than outside

Ensures contaminants do not escape into the lab

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🔄 Recirculation vs Removal

- Filters and recirculates air back into the lab

- Does not fully remove contaminants

- Safety depends on filter efficiency, not elimination

🧪 Chemical-Specific Adsorption

- Uses activated carbon (selective adsorption)

- Only effective for certain chemicals

- Not suitable for all gases or volatile compounds

⚠️ Finite Capacity & Breakthrough

- Filters have limited capacity

- Can fail suddenly when saturated

- Failure is often not immediately noticeable

🌬️ Airflow–Efficiency Trade-Off

- Higher airflow → better capture

- But reduces contact time → lower filtration efficiency

- Performance depends on operating conditions