Environmental, Health and Safety Services

Biosafety Levels / Containment Levels

Type:Abbreviation:Sets Safety Standards and Requirements For Research Using: Source and Reference:
Biosafety LevelsBSL-1 – BSL-4Infectious biological agents (microbes, viruses, etc.)CDC/ NIH

BMBL, 5th Ed.
Section IV
Physical Containment/ Biosafety LevelsBL-1 – BL-4Recombinant or synthetic nucleic acid molecules; recombinant or synthetic nucleic acid molecules and biological agents/ lab animalsNIH

NIH Guidelines
Appendix G
Animal Biosafety LevelsABSL-1 – ABSL-4Infectious biological agents and animalsCDC/ NIH

BMBL, 5th Ed.
Section V
Physical and Biological Containment/ Biosafety Levels – AnimalsBL1-N – BL3-N Recombinant or synthetic nucleic acid molecules and loose-housed animalsNIH

NIH Guidelines
Appendix Q
Biosafety Level 3Ag (Agriculture)BSL-3AGHigh-risk pathogens and large agricultural animals or agricultural plants where facility barriers provide primary containment USDA, CDC/NIH

BMBL, 5th Ed.
Appendix D
Arthropod Containment LevelsACL 1-4Arthropods of public health importance The American Committee of Medical Entomology

Arthropod Containment Guidelines, Version 3.1
Plant Biosafety LevelsBL-1P –BL4-PGreenhouse-based recombinant plants, plant-associated microbes or small animals (arthropods)NIH

NIH Guidelines
Appendix P

Biosafety Levels (BSL-1 – BSL-4)
CDC/ NIH; BMBL, 5th Ed.

  • Combinations of 1) laboratory practices and techniques, 2) safety equipment including Personal Protective Equipment, and 3) facilities features that define the conditions used for safe manipulation of infectious agents.
  • Levels of containment range from the lowest Biosafety Level, BSL-1, to the highest at BSL-4 where the most stringent measures are taken to prevent exposure to/ release of biohazardous agents.
  • See a summary of Biosafety Levels in Biosafety in Microbiological and Biomedical Laboratories, 5th Ed. (BMBL), Section IV, p. 59.


  • Biosafety Levels should not be confused with Risk Groups. Risk Groups are a means of classification of microorganisms based on their association with, and resulting severity of, disease in humans.
  • The Risk Group of a biological agent should be one of a number of factors used in determining the appropriate Biosafety Level to be employed in working with that agent.
  • Often, the Risk Group number assigned to a microorganism used in research will be the same as the Biosafety Level number at which research with that microorganism is conducted, but not always. In some risk-prone circumstances, the Biosafety Level must be heightened for added protection from exposure/release of a biohazardous agent.
  • NOTE: Risk Groups, as defined below, apply to healthy adults; immunocompromised individuals are more vulnerable to infectious disease and thus could be at greater risk if exposed.
  • See a classification of Risk Groups in the BMBL, 5th Ed., Section II, p. 10:


Physical Containment/ Biosafety Levels (BL-1 – BL-4)
NIH; NIH Guidelines

  • As defined in The NIH Guidelines for Research Involving Recombinant DNA Molecules, Appendix G, these levels define parameters that serve to 1) contain recombinant DNA molecules , 2) confine organisms that contain them, and 3) reduce the potential for exposure of lab workers, persons outside the lab, and the environment to that recombinant material.
  • These containment levels are designated as BL1 – BL4, with the highest BL level defining the most stringent containment measures and protective practices.
  • NOTE: The descriptions of NIH’s Biosafety Levels (BLs), are based on existing approaches to the containment of pathogenic organisms, i.e., biosafety levels (BSLs), as described in Biosafety in Microbiological and Biomedical Laboratories, 5th Ed. However, because different combinations of measures may be appropriate for specific research activities involving recombinant studies, The NIH Guidelines allow for alternative selections of primary containment in certain circumstances.
  • While BL levels encompass certain lab practices, containment equipment and facility design features just as the BSL designations do, emphasis here is placed on the primary means of physical containment, which are provided by lab practices and containment equipment.
  • See the NIH Guidelines, Appendix G, for details.

Animal Biosafety Levels (ABSL-1 – ABSL-4)
CDC/ NIH; BMBL, 5th Ed.

  • The practices, safety equipment and facilities features used for experiments with animals involved in infectious disease research or other studies that may require containment.
  • The four levels, designated Animal Biosafety Level (ABSL) 1-4, provide increasing levels of protection to personnel and to the environment, and are recommended as minimal standards for activities involving infected laboratory animals.
  • See a summary of Animal Biosafety Levels in Biosafety in Microbiological and Biomedical Laboratories, 5th Ed., Section V, p. 103:



Physical and Biological Containment/ Biosafety Levels
– Animals (BL1-N – BL3-N)
NIH; NIH Guidelines

  • These levels specify containment and confinement practices for recombinant research involving larger, often loose-housed animals, including:
    • Those in which the animal’s genome has been altered by stable introduction of recombinant or synthetic nucleic acid molecules (or DNA derived therefrom) into the germ-line (transgenic animals)
    • Experiments involving viable microorganisms modified with recombinant or synthetic nucleic acid molecules which are tested on whole animals.
  • As defined by The NIH Guidelines for Research Involving Recombinant DNA Molecules, Appendix Q, these levels apply when research animals are of a size or have growth requirements that preclude the use of containment for lab animals as described in the NIH Guidelines, Appendix G. Such larger species include, but are not limited to, cattle, swine, sheep, goats, horses and poultry.
  • These containment levels are designated by NIH as BL1-N – BL3-N, with the highest BL-N level defining the most stringent containment measures and protective practices.
  • Examples of measures specified by BL-N include:
    • Disposal procedures for animals
    • Animal facility access
    • Decontamination and inactivation procedures
    • Signage
    • Protective clothing
    • Recordkeeping
    • Transfer of materials procedures
  • See NIH Guidelines, Appendix Q, for details.

Biosafety Level 3Ag (BSL-3Ag)
USDA, CDC/NIH BMBL, 5th Ed

  • This biosafety level was created for special situations in which high containment is required in an agricultural setting to prevent agent escape into the environment, due to the risk the agent poses in causing animal disease, zoonotic disease, and/or serious economic impact.
  • BSL-3Ag describes facility parameters and work practices used for research on high-risk pathogens and large, loose-housed, agricultural animals, or other similar situations, where the facility barriers serve as primary containment.
  • Examples of measures prescribed by BAL-3Ag are:
    • Personnel change and shower rooms
    • Self-closing and lockable access doors
    • Double-door autoclaves (all waste is decontaminated before leaving containment)
    • Dedicated, directional air-flow with pressure gauges and alarmed monitoring
    • HEPA filtered supply and exhaust air flow
    • Liquid effluent is collected and decontaminated in a central liquid waste system before disposal into sanitary sewers
    • Interior surface penetrations are sealed; ductwork is airtight; doors are sealed to airtight requirements
  • Plant research has sometimes been placed under this designation.
  • For more details, see Biosafety in Microbiological and Biomedical Laboratories, Appendix D.

Arthropod Containment Levels (ACL 1-4)
The American Committee of Medical Entomology of
the American Society of Tropical Medicine and Hygiene

Arthropod Containment Guidelines, Version 3.1





  • These levels address the unique containment challenges presented by arthropods, and provide increasingly stringent measures for standard and special practices, equipment providing primary barriers, and facilities providing secondary barriers.
  • ACL 1-4 are designed to be consistent with the NIH Guidelines for recombinant research, and with BMBL for research involving arthropod-transmitted microbiological pathogens.
  • Examples of containment measures prescribed by these levels:
    • use of appropriately-sized screen mesh
    • effective trapping methods for escaped arthropods
    • specific waste handling procedures
    • limits on lab access
    • primary containment provided by glove box, walk-in incubator, screen cubicle, etc.
  • See Table 1. Summary of Arthropod Containment Levels in Arthropod Containment Guidelines, Version 3.1, p. 50:


Summary of Arthropod Containment Levels
Active Local VBD Cycling means that transmission of vector-borne diseases of public health importance that are known to be or probably transmitted by the arthropod are cycling in the area.

For further information, see:

Plant Biosafety Levels for Greenhouse Research (BL-1P –BL4-P)
NIH Guidelines

  • NOTE: Plant growth for research carried out in the laboratory (in tissue culture rooms, in growth chambers, at the bench, etc.) should be conducted under the guidelines of the appropriate Biosafety Level. Plant Biosafety Levels are specific to greenhouse settings.
  • The principal purpose of plant containment as defined by these levels is to protect the environment from transmission or release of recombinant or synthetic nucleic acid molecule-containing plant genomes. These levels specify greenhouse practices and greenhouse facility features for physical containment of experiments using recombinant plants, plant-associated microbes, and small animals:
    • As defined in NIH Guidelines, Appendix P, applicable plants include (but are not limited to) mosses, liverworts, macroscopic algae, and vascular plants including terrestrial crops, forest and ornamental species.
    • Plant-associated microorganisms include viroids, virusoids, viruses, bacteria, fungi, protozoans, certain small algae and microbes that have a benign or beneficial association with plants, including those which are being modified to foster an association with plants.
    • Plant-associated small animals include
      • arthropods that are in obligate association with plants, are plant pests or pollinators, that transmit plant diseases
      • other small animals such as nematodes for which testing of their biological properties require the use of plants.
  • Plant biosafety levels BL- 1P – 4P for greenhouse research, as described in NIH Guidelines Appendix P, are summarized below:
    Plant Biosafety LevelApplies to:
    Biosafety Level 1PResearch plants that have low environmental risk; no evidence of harmful impact, survival or spread.
    Biosafety Level 2PResearch plants that could live in the environment with negligible impact, or impact could be readily managed. Includes transgenics capable of interbreeding with weeds/related species, transgenics that use the entire genome of an indigenous infectious agent/pathogen, and plant-associated, indigenous or exotic microbes that are potentially harmful, but harm could be managed.
    Biosafety Level 3PResearch plants that have the potential for detrimental impact on the environment (exotic infectious plants, transgenic plants, transgenic microbes).
    Biosaftey Level 4PPlant research that involves readily transmissible infectious agents that are potentially serious pathogens for major US crops.
  • Examples of criteria to be used for Plant Biosafety Levels include:
    • Greenhouse access
    • Recordkeeping requirements
    • Decontamination and Inactivation requirements
    • Facilities requirements/ greenhouse design
    • Signage
    • Transfer of materials requirements
  • For additional details, see A Practical Guide to Containment – Plant Biosafety in Research Greenhouses.