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Do You Know All the Biosafety Levels?

Most lab professionals know four biosafety levels, but BSL2+ and BSL3+ are also important to know

Jonathan Klane, M.S.Ed., CIH, CSP, CHMM, CIT

Jonathan Klane, M.S.Ed., CIH, CSP, CHMM, CIT, is senior safety editor for Lab Manager. His EHS and risk career spans more than three decades in various roles as a...

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Look at almost any biosafety reference, source, or article and they all say the same thing, “There are four biological safety levels—BSL1, BSL2, BSL3, and BSL4." But what if your lab needs another level for certain hazardous agents or riskier processes?

Aren’t there just four biosafety levels (BSLs)?

Yes and no. There are four BSLs as we know from many sources—even the Biosafety in Microbiological and Biomedical Laboratories, or BMBL, lists four biosafety labs as BSL1 through BSL4. But sometimes biohazards and our processes don’t fit neatly into a certain level. Sometimes we need an in-between level to manage elevated risks by using enhanced practices.

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Why are there two BSL+ levels?

Think of the myriad agents as being on a spectrum with many offshoots. Most can be fit into four risk groups well enough as is. A few of the agents don’t fit well, and sometimes the processes in use increase the risks. So, we need to modify BSL2 and BSL3 for these few times. These vary between BSL labs and organizations with labs. One constant is that there isn’t one consistent list of these. Specific risk assessments are key.


There are three aspects to focus on for BSL2+ risk assessing and risk managing— agents, processes, and enhanced 2+ practices.

2+ agents: 

Processes with added risks: 

  • Practices with a greater probability or exposure of airborne route of entry
  • Higher volumes or concentrations of culture
  • Procedures deliberately generating aerosols
  • High-speed cell sorter
  • High pressure (e.g., 30-60 psi or greater)
  • Potential for aerosolization

Enhanced 2+ practices: 

  • All of BSL2 applies
  • Plus using some BSL3 practices, such as:
    • Specialized training on the risks and how to mitigate them
    • The use of wrap-back disposable gowns and wearing double gloves
    • Respiratory protection when handling material outside a biosafety cabinet
    • Restricting access to rooms when experiments are conducted
    • Lockable doors

Now, let’s look at when a BSL3+ lab might be needed. They’re rare and this may be your first time learning about them.


BSL3+ labs are far less commonly done. Because of their rare use, it’s hard to find helpful information about them. The same three aspects require our attention—agents, processes, and enhanced 3+ practices.

3+ agents: 

Processes with added risks: 

Enhanced 3+ practices:

How to decide if your lab needs to use a BSL2+ or BSL3+

It’s all about risk. If your lab has pathogens or agents in a BSL2 or BSL3 lab with processes that increase risks, you may need to implement a +level approach. Assess your lab and process-specific risks, then decide based on the risk analysis. Good luck!

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