There is sometimes confusion between biological safety levels and the different classes and types of biosafety cabinets. While these terms are somewhat related, their purpose is very different.
Biosafety safety levels are set by the U.S. Centers for Disease Control and Prevention and the National Institute of Health, and provide biocontainment guidelines for biocontainment labs working with dangerous biological agents. Here is how the different levels are defined.
BSL1 labs are suitable for work involving well-characterized agents of no known or of minimal potential health hazard to healthy adults.
BSL2 labs are suitable for work involving agents of moderate potential hazard to personnel and the environment. Agents that may produce disease of varying degrees of severity from exposure by injection, ingestion, absorption, and inhalation.
From the National Emerging Infectious Diseases Laboratories (NEIDL) at the Boston University Medical Campus, in this video (from www.bu.edu) James Galagan, PhD, Associate Professor of Biomedical Engineering and Microbiology, describes his research on a non-pathogenic close relative of the organism that causes TB: Mycobacterium smegmatis in his BSL 2 Lab.