“Biosafety Levels” (BSLs) are designations applied to projects or activities conducted in laboratories in ascending order of containment based on the severity of the health-related risk associated with the work being conducted. In the United States, the designations BSL-1, BSL-2, BSL-3, and BSL-4 describe the minimum safe work practices, specially designed buildings, and safety equipment required to conduct work on infectious agents, toxins, and other biological hazards. BSL-4 is the highest biosafety level.
The appropriate BSL to be assigned to a project is determined by institutional biosafety committees (IBCs) or professionals, and reflects the specific combinations of specially designed buildings, safety equipment and safe work practices that laboratory workers must use. The BSL assigned to a project is based on a biological risk assessment that takes into account:
- The nature of the infectious agent, toxin, or biological hazard, including:
- Its ability to cause disease and the way in which it causes disease (transmissibility and pathogenicity);
- How much of it is required to cause disease (infectious dose);
- How many different organisms are susceptible to it (host range); and
- It’s prevalence in the community (epidemiology);
- The specific laboratory activity or activities being performed; and
- The availability of preventive medical countermeasures (i.e. vaccines) or effective treatment (i.e., post-exposure vaccination and/or use of antimicrobials, antivirals and chemotherapeutic agents).
The “BSL” terms for laboratory work with infectious agents, toxins, or other biological hazards affecting plants are BL1-P, BL2-P, BL3-P, and BL4-P and are in ascending order of containment based on the degree of the health-related risk associated with the work being conducted.
The “BSL” terms for laboratory work with infectious agents, toxins, or other biological hazards affecting animals are ABSL-1, ABSL-2, ABSL-3, BSL3-Ag, and ABSL-4, and are in ascending order of containment based on the degree of the health or environmental-related risk associated with the work being conducted.