The 4 standard biosafety levels are:
- Level 1 -- This level applies to agents that do not ordinarily cause human disease.
- Level 2 -- This level is appropriate for agents that can cause human disease, but whose potential for transmission is limited.
- Level 3 -- This level applies to agents that may be transmitted by the respiratory route which can cause serious infection.
- Level 4 -- This level is used for the diagnosis of exotic agents that pose a high risk of life-threatening disease, which may be transmitted by the aerosol route and for which there is no vaccine or therapy.