Biosafety level sign (BSL-1 to BSL-4)
A sign with the biohazard symbol and a biosafety level, BSL-1 to BSL-4, tells you what level of containment a lab works at. BSL-1 is for agents not known to cause disease in healthy adults; BSL-4 is for dangerous agents with no vaccine or treatment.
How to read it
Biosafety levels are set out in Biosafety in Microbiological and Biomedical Laboratories (BMBL), published by the CDC and the National Institutes of Health. For each level it says a sign is posted at the lab entrance when infectious materials are present, giving the lab’s biosafety level, the name and telephone number of the supervisor or other responsible person, and the protective equipment required. From BSL-2 up the BMBL says the sign incorporates the universal biohazard symbol. Kansas State University’s lab signs show the biosafety level beside the biohazard symbol and leave out which agents are present.
Also searched as: biohazard door sign, biosafety level 2 sign, biosafety level symbol, BSL-1, BSL-2, BSL-2 sign, BSL-3, BSL-4, BSL sign.
These explain what each sign means and which standard sets it. What to do in a laboratory is set by the lab’s own rules, signs and trained staff; for a chemical, refer to its label and safety data sheet.
The four levels
The CDC’s training says each biosafety level builds on the controls of the level before it.
| Level | What the BMBL says it is for | An example from the CDC |
|---|---|---|
| BSL-1 | Well-characterized agents not known to consistently cause disease in healthy adults, with minimal hazard | A nonpathogenic strain of E. coli |
| BSL-2 | Agents that cause human disease and pose moderate hazards | Staphylococcus aureus |
| BSL-3 | Agents that may cause serious or potentially lethal disease through inhalation | Mycobacterium tuberculosis |
| BSL-4 | Dangerous and exotic agents with a high risk of aerosol-transmitted infection, frequently fatal, with no vaccines or treatments | The CDC notes there are a small number of BSL-4 labs worldwide |
BSL-1 and BSL-2 signs
The BMBL’s text for BSL-1 asks for a sign with the level and contacts but does not mention the biohazard symbol; from BSL-2 the sign incorporates it. The University of Houston’s door signs have separate pictograms for Biosafety Level 1 and Biosafety Level 2, and describe BSL-1 labs as working with microbes that pose little to no threat of infection in healthy adults.
The US rule for HIV and HBV labs
OSHA’s bloodborne pathogens standard sets its own sign for HIV and HBV research laboratories: a hazard warning sign with the universal biohazard symbol on all access doors, fluorescent orange-red or predominantly so, with lettering and symbols in a contrasting colour.
Read next
- Next in Lab safety symbolsWear eye protection sign (M004)A blue circle with a white head wearing goggles means eye protection must be worn where the sign is posted. It is sign M004 in ISO 7010, the international standard for safety signs.
- The biohazard symbol a BSL-2 to BSL-4 sign incorporates.Biohazard symbolA warning of a biological hazard: infectious agents that present a risk of death, injury or illness.
More lab safety symbols
The same shape elsewhere
Browse symbols drawn with circles, curves and waves or letters and numbers.
Sources
- Biosafety in Microbiological and Biomedical Laboratories, 6th edition, BMBL 6th edition (revised June 2020), U.S. Centers for Disease Control and Prevention and National Institutes of Health, via NIH Office of Research Services, Section IV, BSL-1 to BSL-4 standard practices
- Recognizing the Biosafety Levels (Quick Learn), U.S. Centers for Disease Control and Prevention, BSL-1 to BSL-4
- Laboratory Doorsigns, University of Houston Environmental Health and Safety, Hazards
- K-State Laboratory Signs, Kansas State University Environmental Health and Safety, Biohazard Symbol
- Bloodborne pathogens (29 CFR 1910.1030), 29 CFR 1910.1030, U.S. Occupational Safety and Health Administration, 1910.1030(e)(2)(ii)(D), (g)(1)(ii)
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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