16 Biosafety Manual D. Biosafety Practices and Procedures Work Practices (First Line Of Defense) Safe work practices are the most critical part of preventing exposure when working with biohazardous materials. The best laboratory and safety equipment available cannot provide protection unless personnel use good work practices and have adequate training. Additional safe work practices may be critical at preventing exposure to non biohazardous materials. Safe work practices that apply to all laboratories at ISU are covered in the Laboratory Safety Manual . Laboratory Biosafety Level Criteria The four biosafety levels (BSL) provide guidelines to ensure appropriate protection for laboratory users and the environment based on biological risk. Biological risk is related to the infectious agent used, the pathogenicity of the agent, and the mode of transmission. A wide variety of requirements for both physical containment and procedural details comes with increasing levels of protection. The Biosafety in Microbiological and Biomedical Laboratories (BMBL), published by CDC and NIH, lists proper practices, procedures, and facilities for each biosafety level. • BSL-1 is suitable for work involving well-characterized agents not known to consistently cause disease in immunocompetent adult humans, and present minimal potential hazard to laboratory personnel and the environment. • BSL-2 builds upon BSL-1. BSL-2 is suitable for work involving agents associated with human disease that pose moderate hazards to personnel and the environment. • BSL-3 is applicable to clinical, diagnostic, teaching, research, or production facilities where work is performed with indigenous or exotic agents that may cause serious or potentially lethal disease through the inhalation route of exposure. • BSL- 4 is required for work with dangerous and exotic agents that pose a high individual risk of aerosol-transmitted laboratory infections and life-threatening disease that is frequently fatal, for which there are no vaccines or treatments, or a related agent with unknown risk of transmission.