Four Levels of Biosafety
BSL 1: Material not known to consistently cause disease in healthy adults.
BSL 2: Associated with human disease. Hazard is from percutaneous injury, ingestion, or mucous membrane exposure.
BSL 3: Indigenous or exotic agents with potential for aerosol transmission; disease may have serious or lethal consequences.
BSL 4: Dangerous/exotic agents which pose a high risk of life-threatening disease, aerosol-transmitted lab infections or related agents with unknown risk of transmission.