Environmental Health and Safety

The principles of biohazard control center on the concept of containment, which refers to safe methods of managing infectious agents in the laboratory environment where they are being handled or maintained. The purpose of containment is to reduce or eliminate exposure of laboratory personnel, other persons and the outside environment to potentially hazardous agents.

Primary containment involves the protection of personnel in the immediate laboratory environment from exposure to infectious agents, and is provided by good microbiological technique, the use of proper safety equipment and appropriate vaccines. Secondary containment refers to the protection of the environment external to the laboratory from exposure to infectious materials and is provided by a combination of facility design and operational practices. The three major elements of containment are:

a. Laboratory Practices and Techniques
b. Safety Equipment
c. Facility Design and Construction

Persons working with infectious agents or potentially infected materials must be aware of potential hazards and must be trained and proficient in the microbiological practices and techniques required to handle such material safely.

Each laboratory shall comply with practices and procedures specified in this Biohazard Control Program Manual to minimize or eliminate exposures to these hazards.

Additional safety practices shall be developed and implemented when standard biosafety practices are not sufficient to control the hazards associated with a particular agent or laboratory procedure. Safety practices and techniques must be supplemented by appropriate facility design and engineering features, safety equipment and management practices.

Biological Safety Cabinets or Biosafety Cabinets (BSCs) are among the most effective and widely used devices for providing primary containment. The three types of BSCs - Class I, II, and III - have varying design and performance characteristics.

The Class I biosafety cabinet (BSC) is a negative-pressure, ventilated cabinet usually operated with an open front and a minimum face velocity at the work opening of at least 75 linear feet per minute (lfpm). All of the air from the BSC is exhausted through a HEPA filter either into the laboratory or to the outside. The Class I BSC is designed for general microbiological research with low- and moderate-risk microorganisms (i.e., BSL 1 and 2 agents), and is useful for containment of mixers, blenders, and other equipment. These BSCs are not appropriate for handling research materials that are vulnerable to airborne contamination, since the inward flow of unfiltered air from the laboratory can carry microbial contaminants into the BSC. Class I BSCs are not approved for use at SDSU.

The Class II BSC is designed with inward airflow at a velocity to protect personnel (75-100 lfpm), HEPA-filtered downward vertical laminar airflow for product protection and HEPA-filtered exhaust air for environmental protection. When used in conjunction with good microbiological techniques, Class II BSCs provide an effective containment system for the safe manipulation of moderate to high-risk microorganisms (i.e., BSL 2 and 3 agents). They also provide protection from external contamination of the materials (e.g., cell cultures, microbiological stocks) being manipulated inside the BSC.

The Class III BSC is a totally enclosed, ventilated cabinet of gas-tight construction and offers the highest degree of personnel and environmental protection from infectious aerosols, as well as protection of research materials from microbiological contaminants. Class III BSCs are most suitable for work with hazardous microorganisms (i.e., BSL 3 agents). All operations are performed through attached arm-length rubber gloves or half-suits. The Class III BSC is operated under negative pressure. Supply air is HEPA-filtered and the BSC exhaust air is filtered through two HEPA filters in series, or HEPA filtration followed by incineration, before discharge outside of the facility.

All equipment required by the laboratory activity, such as incubators, refrigerators, and centrifuges, must be an integral part of the BSC system. The Class III BSC must be connected to a double-doored autoclave and/or chemical dunk tank used to sterilize or disinfect all materials exiting the BSC and to allow supplies to enter the BSC. Several Class III BSCs are therefore typically set up as an interconnected system.

See Appendix A of CDC/NIH publication Biosafety in Microbiological and Biomedical Laboratories (4th Ed., 1999) for a description of the design and use of BSCs.

All BSCs must be tested and certified in situ at the time installation in the laboratory is complete, any time the BSC is moved and at least annually thereafter. All laboratory personnel must be trained in the proper use of these devices.

The safety centrifuge cup is another example of a primary containment. It is an enclosed container designed to prevent aerosols from being released during centrifugation, to be used when handling infectious agents that can be transmitted through the aerosol route of exposure.

Safety equipment also includes items for personal protection, such as gloves, coats, gowns, shoe covers, boots, respirators, face shields, safety glasses or goggles. Personal protective equipment (PPE) is often used in combination with BSCs and other devices that contain the agents, animals or materials being handled.

The design and construction of the facility contributes to the laboratory staffs' protection, provides a barrier to protect persons outside the laboratory and protects persons or animals in the community from infectious agents which may be accidentally released from the laboratory.

The recommended secondary containment will depend on the risk of transmission of specific agents. For example, secondary containment in BSL 1 and 2 facilities may include separation of the laboratory work area from public access, availability of a decontamination facility (e.g., autoclave) and handwashing facilities.

When the risk of infection by exposure to an infectious aerosol is present, higher levels of primary containment and multiple secondary containment may become necessary to prevent infectious agents from escaping into the environment. Such design features include specialized ventilation systems to ensure directional airflow, air treatment systems to decontaminate or remove agents from exhaust air, controlled access zones, airlocks as laboratory entrances or separate buildings or modules to isolate the laboratory. Specific ventilation recommendations can be found in the Applications Handbook for Heating, Ventilation, and Air-Conditioning (HVAC) published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).

Four biosafety levels (BSLs) are described that consist of combinations of the laboratory practices and techniques, safety equipment and facility design and construction appropriate for the operations performed and the hazards posed by the infectious agents in question. These levels are designated in ascending order by degree of protection provided to personnel, the environment and the community (i.e., BSL 1-4).