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Recognizing the Biosafety Levels

Recognizing the Biosafety Levels

This Quick Learn Lesson will take approximately 15 minutes to complete.

When you have completed this lesson, you will be able to recognize characteristics of the four biological safety levels.

Biohazard sign for a biosafety level 2 laboratory. It states biosafety level 2, authorized personnel only.

Introduction

Suppose you are a laboratory microbiologist working with a potentially harmful microbe. Precautions must be taken in the laboratory to make sure you and others are not infected.

  • Where in the lab would you complete your work?
  • What protective equipment and practices would you use?
  • How would you contain the microbe to limit contamination or accidental infection?

These are just a few of the questions that can be answered through an understanding of biosafety and the four biosafety levels (BSLs).



Biosafety and Biosafety Levels

What is Biosafety?
Biosafety is the application of safety precautions that reduce a laboratorian’s risk of exposure to a potentially infectious microbe and limit contamination of the work environment and, ultimately, the community.

What are Biosafety Levels (BSLs)?
There are four biosafety levels. Each level has specific controls for containment of microbes and biological agents. The primary risks that determine levels of containment are infectivity, severity of disease, transmissibility, and the nature of the work conducted. Origin of the microbe, or the agent in question, and the route of exposure are also important.

Each biosafety level has its own specific containment controls that are required for the following:

  • Laboratory practices
  • Safety equipment
  • Facility construction


BSLs, continued

The biosafety levels range from BSL-1 to BSL-4. Each biosafety level builds on the controls of the level before it. Every microbiology laboratory, regardless of biosafety level, follows standard microbiological practices.

Pyramid showing the four BSLs with the lowest risk microbes at the bottom, representing BSL-1, and the highest risk microbes at the top, representing BSL-4.

You will learn about each level on the following screens.



BSL-1

Pyramid showing the four BSLs with the lowest risk microbes highlighted at the bottom, representing BSL-1. Levels 2-4 are grey.

If you work in a lab that is designated a BSL-1, the microbes there are not known to consistently cause disease in healthy adults and present minimal potential hazard to laboratorians and the environment. An example of a microbe that is typically worked with at a BSL-1 is a nonpathogenic strain of E. coli.

Specific considerations for a BSL-1 laboratory include the following:

Laboratory practices

  • Standard microbiological practices are followed.
  • Work can be performed on an open lab bench or tableA.

Safety equipment

Facility construction

  • A sink must be available for hand washing.
  • The lab should have doors to separate the working space with the rest of the facility.

    Man working in a BSL-1 lab wearing a lab coat, safety glasses, and gloves while pouring liquid into a beaker on an open lab bench.


BSL-2

Pyramid showing the four BSLs with BSL-2 highlighted. Levels 1, 3, and 4 are grey.

BSL-2 builds upon BSL-1. If you work in a lab that is designated a BSL-2, the microbes there pose moderate hazards to laboratorians and the environment. The microbes are typically indigenous and associated with diseases of varying severity. An example of a microbe that is typically worked with at a BSL-2 laboratory is Staphylococcus aureus.



BSL-2, continued

In addition to BSL-1 considerations, BSL-2 laboratories have the following containment requirements:

Laboratory practices

  • Access to the laboratory is restricted when work is being conducted.

Safety equipment

  • Appropriate personal protective equipment (PPE) A is worn, including lab coats and gloves. Eye protection and face shields can also be worn, as needed.
  • All procedures that can cause infection from aerosols or splashes are performed within a biological safety cabinet (BSC)B.
  • An autoclave or an alternative method of decontamination is available for proper disposals.

Facility construction

  • The laboratory has self-closing doors.
  • A sink and eyewash are readily available.

    Woman working in a BSL-2 laboratory. She is wearing gloves, a face shield, a lab coat and is conducting work within a biological safety cabinet.


BSL-3

Pyramid showing the four BSLs with BSL-3 highlighted. Levels 1, 2, and 4 are grey.

BSL-3 builds upon the containment requirements of BSL-2. If you work in a lab that is designated BSL-3, the microbes there can be either indigenous or exotic, and they can cause serious or potentially lethal disease through respiratory transmission. Respiratory transmission is the inhalation route of exposure. One example of a microbe that is typically worked with in a BSL-3 laboratory is Mycobacterium tuberculosis, the bacteria that causes tuberculosis.



BSL-3, continued

In addition to BSL-2 considerations, BSL-3 laboratories have the following containment requirements:

Laboratory practices

  • Laboratorians are under medical surveillance and might receive immunizations for microbes they work with.
  • Access to the laboratory is restricted and controlled at all times.

Safety equipment

  • Appropriate PPE must be worn, and respirators might be requiredA.
  • All work with microbes must be performed within an appropriate BSCB.

Facility construction

  • A hands-free sink and eyewash are available near the exit.
  • Exhaust air cannot be recirculated, and the laboratory must have sustained directional airflow by drawing air into the laboratory from clean areas towards potentially contaminated areas.
  • Entrance to the lab is through two sets of self-closing and locking doorsC.

    Man working in a BSL-3 lab wearing PPE, including a powered air purifying respirator. He is working within a BSC. Self-closing locked doors are in the background of the work station.


BSL-4

Pyramid showing the four BSLs with the highest risk level, BSL-4, highlighted at the top. Levels 1-3 are grey.

BSL-4 builds upon the containment requirements of BSL-3 and is the highest level of biological safety. There are a small number of BSL-4 labs in the United States and around the world. The microbes in a BSL-4 lab are dangerous and exotic, posing a high risk of aerosol-transmitted infections. Infections caused by these microbes are frequently fatal and without treatment or vaccines. Two examples of microbes worked with in a BSL-4 laboratory include Ebola and Marburg viruses.



BSL-4, Continued

In addition to BSL-3 considerations, BSL-4 laboratories have the following containment requirements:

Laboratory practices

  • Change clothing before entering.
  • Shower upon exiting.
  • Decontaminate all materials before exiting.

Safety equipment

Facility construction

  • The laboratory is in a separate building or in an isolated and restricted zone of the building.
  • The laboratory has dedicated supply and exhaust air, as well as vacuum lines and decontamination systems.

    Woman working in a BSL-4 laboratory. She is wearing a full positive pressure suit. No skin is exposed; her air supply can be seen on the back of her suit. She working within a BSC.


Your Turn: Exercises

Now that you have learned about the four biosafety levels, it's your turn to identify the correct BSL in the examples on the following screens. Select the Next icon to begin.



Your turn: Exercise 1

Select the biosafety level described by the conditions of the following example. Levels are listed below.

A microbiology graduate student is working on a project under the following conditions:

  • Work is conducted on a standard laboratory table or bench.
  • A nonpathogenic laboratory strain of E. coli is being used.
  • Minimal PPE, such as a lab coat, gloves, and eye protection might be worn but are not necessary.



Your turn: Exercise 2

Select the biosafety level shown in the photo below. Click on the photo for a larger image.

Man is wearing a powered air purifying respirator, gloves, and solid-front gown. He is working within a BSC, and self-closing, locked doors are in the background.


Your turn: Exercise 3

Select the biosafety level described by the conditions of the following example. Levels are listed below.

  • Work is conducted on a standard laboratory bench in a contained area.
  • PPE, including a lab coat, gloves, and eye protection are being used to reduce accidental infection.



Your turn: Exercise 4

Select the biosafety level shown in the following photograph below. Click on the photo for a larger image.

Man is wearing a powered air purifying respirator, gloves, and solid-front gown. He is working within a BSC, and self-closing, locked doors are in the background.

Man is wearing a powered air purifying respirator, gloves, and solid-front gown. He is working within a BSC, and self-closing, locked doors are in the background.



Summary

Congratulations!

You should now be able to recognize characteristics of the four biological safety levels. If you would like additional information or resources on the topic of biosafety, select the Next icon. To view other Quick Learn Lessons, visit CDC Learning Connection.



Resources

For more information on biosafety and laboratory practice, review the following web resources: