Biosafety levels describe the level of biosafety precautions necessary to contain infectious agents. Like risk groups (RGs), the levels of containment range from the lowest biosafety level 1 (BSL-1) to the highest at level 4 (BSL-4). Biosafety controls – work practices, equipment, and facilities – increase as the scale of risk increases.
The essential elements of the four biosafety levels and the type of work associated with them are described below.
Laboratory has doors for access control and a sink for handwashing; surfaces are easy to clean; windows are screened (much like a kitchen).
Appropriate for work with microorganisms not known to consistently cause disease in healthy adult humans.BSL-2: BSL-1 lab plus the door is self-closing and lockable for restricted access; the sink is located near the exit; there is access to an autoclave or other waste decontamination method; an eyewash station is present. All work that might create aerosols of infectious materials is done in a biosafety cabinet.
Appropriate for agents associated with human disease resulting from percutaneous injury (cuts, needle sticks), ingestion, mucous membrane exposure.
- BSL-3:BSL-2 lab plus the lab is separated or isolated from the main building traffic flow; double door entry is provided; inward directional airflow is provided with visual indicators; all work with viable agent is performed in a biosafety cabinet or other equipment designed to contain aerosols; sinks are hands-free or automatically operated; seams, floors, walls & ceilings are sealed to facilitate space decontamination; waste decontamination systems are available in the facility but preferred to be in the lab.
Appropriate for agents with potential for aerosol transmission; disease may have serious or lethal consequences.
- BSL-4:BSL-3 lab plus the lab is in a separate building or a clearly demarcated and isolated zone within a building; provides a chemical shower and personal shower for exiting; has a double door/pass through autoclave present in the lab; rooms are tightly sealed for no passage of air; doors for entry are interlocked so they can not be opened at the same time; liquids are decontaminated through engineered system; a multi-level facility with redundancies in engineering controls such as HVAC. When dealing with biological hazards at this level, PPE with a self-contained oxygen supply is mandatory. BSL-4 work is not conducted at UGA.
Appropriate for dangerous/exotic agents that pose a high risk of life-threatening disease, aerosol-transmitted lab infections; or related agents with unknown risk of transmission, and for which there is no available vaccine or therapy.
Four biosafety levels are also established and defined for infectious disease work with vertebrate animals: Animal Biosafety Levels (ABSL) 1, 2, 3 and 4. These biosafety levels provide increasing levels of protection to personnel and the environment through combinations of biosafety controls.
A special biosafety level called BSL-3-Agriculture (or BSL 3-Ag) applies to a list of foreign animal disease agents designated “high consequence” by the USDA, meaning they can have a significant impact on our economy. BSL 3-Ag facilities are specially engineered for work with loose-housed animals infected with these pathogens, (e.g., the laboratory facility itself acts as a primary barrier to prevent release of infectious agents into the environment).
Biosafety levels also are defined for work with arthropods (e.g., mosquitoes and ticks) and genetically modified organisms (e.g., transgenic plants and animals). Biosafety levels applied to arthropods are Arthropod Containment Levels (ACL) 1, 2, 3, and 4.