• 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.

• 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

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.

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

• 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

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

Ensure compliance with strict safety and environmental regulations

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.

- 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

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).

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