Biological Safety Levels (BSL)

A biosafety level is a set of biocontainment precautions required to isolate dangerous biological agents in an enclosed laboratory facility. The levels of containment range from the lowest biosafety level 1 (BSL-1) to the highest at level 4 (BSL-4). In the United States, the Centers for Disease Control and Prevention (CDC) have specified these levels.

At the lowest level of biosafety, precautions may consist of regular hand-washing and minimal protective equipment. At higher biosafety levels, precautions may include airflow systems, multiple containment rooms, sealed containers, positive pressure personnel suits, established protocols for all procedures, extensive personnel training, and high levels of security to control access to the facility.





Primary Barriers and

Safety Equipment


(Secondary Barriers)


Not known to consistently cause diseases in healthy adults

Standard microbiological practices

No primary barriers required.

PPE: laboratory coats and gloves; eye, face protection, as needed

Laboratory bench and sink required


Agents associated with human disease

Routes of transmission include per­cutaneous injury, ingestion, mucous membrane exposure

BSL-1 practice plus:

- Limited access

- Biohazard warning signs

- “Sharps” precautions

- Biosafety manual defining any needed waste decontamination or medical surveillance policies

Primary barriers:

- BSCs or other physical containment devices used for all manipulations of agents that cause splashes or aerosols of infectious materials


PPE: Laboratory coats, gloves, face and eye protection, as needed

BSL-1 plus:

- Autoclave available



Indigenous or exotic agents that may cause serious or potentially lethal disease through the inhalation route of exposure

BSL-2 practice plus:

- Controlled access

-Decontamination of all waste

-Decontamination of laboratory clothing before laundering

Primary barriers:

- BSCs or other physical containment devices used for all open manipula­tions of agents


PPE: Protective laboratory clothing, gloves, face, eye and respiratory protection, as needed

BSL-2 plus:

- Physical separation from access corridors

- Self-closing, double-door access

- Exhausted air not recirculated

- Negative airflow into laboratory

- Entry through airlock or anteroom

- Hand washing sink near laboratory exit


Dangerous/exotic agents which post high individual risk of aerosol-trans­mitted laboratory infections that are frequently fatal, for which there are no vaccines or treatments

Agents with a close or identical anti­genic relationship to an agent requir­ing BSL-4 until data are available to redesignate the level

Related agents with unknown risk of transmission

BSL-3 practices plus:

- Clothing change before entering

- Shower on exit

- All material decontaminated on exit from facility

Primary barriers:

- All procedures conducted in Class III BSCs or Class I or II BSCs in com­bination with full-body, air-supplied, positive pressure suit

BSL-3 plus:

- Separate building or isolated zone

- Dedicated supply and exhaust, vacuum, and decontamination systems


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