Biosafety Levels (BSL) prescribe procedures and containment requirements for the particular microorganism or materials used in research. These levels, which are ranked from one to four, are selected based on the agents or organisms that are handled in a laboratory setting. For example, a basic lab setting specializing in the research of nonlethal agents that pose a minimal potential threat to laboratory workers and the environment are generally considered BSL-1 – the lowest BSL. A specialized research laboratory that deals with potentially deadly infectious agents such as Ebola virus would be designated as BSL-4 – the highest and most stringent BSL.
The Centers for Disease Control and Prevention (CDC) sets BSLs as a way of exhibiting specific controls for the containment of microbes and biological agents. Each BSL builds upon on the previous level—thereby creating layer upon layer of constraints and barriers. BSLs are determined by the following:
- Risks related to containment
- Severity of infection
- Transmissibility
- Nature of the work conducted
- Origin of the microbe
- Agent in question
- Route of exposure