Biological Hazards and Containment in Laboratories

Exam Tip: Remember that Risk Group 3 and 4 both involve high individual risk, but they are differentiated by the risk they pose to the general community.

Containment Levels

The classification of a pathogen into a risk group directly dictates the required Containment Level for handling and storing it. Containment levels refer to the minimum physical features and operational requirements necessary to ensure safety. Generally, the containment level matches the risk group (e.g., Risk Group 2 requires Containment Level 2).

Containment is achieved through a hierarchy of controls:

1. Engineering Controls: The highest level of protection, involving laboratory design, ventilation systems, and specialized equipment.
2. Administrative Controls: Procedures that alter how work is done, such as training, signage, and policy manuals.
3. Personal Protective Equipment (PPE): The last line of defense, including gloves, gowns, and respirators.

Breakdown of Containment Levels

• Containment Level 1: Relies on good microbiological practices and basic physical features, such as handwashing sinks, to protect personnel.
• Containment Level 2: Includes all Level 1 features plus administrative controls (training, PPE) and physical features like Biological Safety Cabinets (BSCs).
• Containment Level 3: Requires stringent engineering controls, such as HEPA filtration of exhaust air, specialized equipment (e.g., centrifuges with sealed rotors), and effluent decontamination systems.

Biological Safety Cabinets (BSC)

The Biological Safety Cabinet (BSC) is the primary engineering control used to protect workers from aerosol exposure. Aerosols are fine mists or droplets that can carry infectious agents; procedures like pipetting, mixing, or vortexing are high-risk activities that should always be performed within a BSC.

HEPA Filtration

The most critical component of a BSC is the HEPA (High Efficiency Particulate Air) filter. These filters are constructed from highly pleated glass and paper fibers designed to remove most particles larger than $0.3 \mu m$ in diameter.

Classification of BSCs

BSCs are categorized into three classes based on their level of protection:

• Class I: Protects the operator from airborne material by drawing air into the cabinet and filtering it before it is exhausted. However, it does not maintain the sterility of the work surface.
• Class II: Protects both the operator and the work product. Air flows in "sheets" that act as barriers, sterilizing the air that flows over the material.
  • Type A1 and A2: Common in clinical labs; they recirculate approximately 70% of the air after HEPA filtration.
  • Type B: These are completely exhausted outside of the building via hard ductwork.
• Class III: A completely enclosed, negative-pressure system that provides the highest level of protection. Material is handled through attached rubber gloves. This is required for Risk Group 4 microorganisms and may be used for Risk Group 3.

Safety Note: BSCs must be certified annually, or after repairs or relocation, by qualified personnel to ensure they are functioning correctly.

Managing Biological Spills

Despite rigorous containment, spills can occur. Every laboratory must have an emergency response plan and a dedicated biological spill kit. A standard kit should include:

• Additional PPE (heavy-duty gloves, face shields, respirators).
• Absorbent materials (paper towels).
• Disinfectant and forceps for handling contaminated sharps.

Standard Spill Procedure:

1. If the spill is large, evacuate the area and allow aerosols to settle for at least 10 minutes.
2. Cover the spill with paper towels.
3. Gently pour disinfectant onto the towels, working from the outside edge toward the center to prevent spreading.
4. Allow the disinfectant to sit for 30 minutes.
5. Use forceps to remove the towels and place them in a biohazard container.