ehs logo

Health & Safety Manual - Biological Safety

2.2 Biosafety Levels and Risk Assessment

2.2.1 Biosafety Level 1 (BSL-1)
2.2.2 Biosafety Level 2 (BSL-2)
2.2.3 Biosafety Level 3 (BSL-3)

2.2.4 Biosafety Level 4 (BSL-4)
2.2.5 Agent Summary Statements

2.2.6 Risk Assessment

Risk is the probability that harm, injury, or, in the context of this document, disease will occur. The foundation of any safety program is the use of control measures appropriate for the risk posed by the activities and the agents in use. To characterize their risk, microorganisms and clinical materials are assigned to one of four Biosafety Levels (BSLs). For each BSL there is a unique set of safety equipment, facility design features, and practices that will reduce the risk of laboratory-acquired infections.

A complete description of work practices, safety equipment, and facility design features for BSL-1 through BSL-4 is available in the CDC/NIH publication Biosafety in Microbiological and Biomedical Laboratories (BMBL 5) 5th Edition, specifically, Section IVThe following excerpts should be considered as general summaries and users are encouraged to review the more comprehensive information on the aforementioned web sites.  The NIH’s Guidelines for Research Involving Recombinant DNA Molecules provide additional information along these lines as well as guidance for risk assessment of microorganisms and materials containing recombinant DNA, which may increase or decrease the risk of the activities.

2.2.1 Biosafety Level 1 (BSL-1)

  • Agents:  defined and characterized strains of microorganisms not known to consistently cause disease in healthy adults e.g., B. subtilis, S. cerevesiae, non-pathogenic E. coli.  Includes recombinant DNA activities using such non-pathogenic organisms as hosts for the expression of genes incorporated into bacterial plasmids or low risk viral vectors such as baculovirus or Adeno Associated Virus.
  • Work practices:  standard microbiological practices/aseptic technique.
  • Safety equipment:  none required-gloves, lab coats and eye protection recommended.
  • Facilities:  bench top sink available for hand washing.

Go to Top

2.2.2 Biosafety Level 2 (BSL-2)

  • Agents:  associated with human diseases of varying severity, e.g., Hepatitis B and C, HIV, S. typhi, human retroviruses, S. aureus.  Includes recombinant DNA activities using viral vector systems such as Adenoviruses and some Retroviral vectors, particularly Lentiviral vectors, and expression of recombinant DNA in BSL-2 organisms.
  • Transmission: inoculation and other percutaneous injuries, ingestion, mucous membrane exposure
  • Work practices:  BSL-1 practices, with the addition of: limited access, ‘Biohazard’ signs, ‘sharps’ precautions, defined procedures for Regulated Medical Waste (RMW) disposal and medical surveillance (as needed).
  • Safety equipment:  Class I or II Biological Safety Cabinet (BSC) or equivalent containment for manipulations with potential for aerosolization or splashing; lab coats, gloves, eye/face protection.
  • Facilities:  BSL-1 facilities, with the addition of: available autoclave, directional airflow, no air recirculation, disinfection/decontamination procedures in place.

2.2.3 Biosafety Level 3 (BSL-3)

  • Agents: serious or lethal diseases transmissible via aerosols, e.g., M. tuberculosis, SARS.  Recombinant DNA activities using genetic material from BSL-3 organisms or such organisms as host cells.
  • Transmission: aerosol inhalation, inoculation and other percutaneous injuries, ingestion, mucous membrane exposure
  • Work practices:  BSL-2 practices, with the addition of: controlled access, on-site decontamination of all waste and lab clothing, medical surveillance.
  • Safety equipment: Class I or II Biological Safety Cabinet (BSC) or equivalent containment for all open manipulations of agents; lab coats, gloves, eye/face, and respiratory protection (as needed).
  • Facilities:  BSL-2 facilities, with the addition of:  physical separation from access corridors, double-door entry, directional air flow into lab, no recirculation of exhaust air, back-up ventilation and filtration systems, in-lab autoclave.

Go to Top

2.2.4 Biosafety Level 4 (BSL-4)
Organisms in this category are of such extremely high risk that only a handful of laboratories nationwide work at this level.  No such facilities exist at the University.

2.2.5 Agent Summary Statements
Agent Summary Statements, including recommended BSL for many laboratory microorganisms, are included in BMBL 5.

Other resources for biosafety hazard classification are noted on the American Biological Safety Association (ABSA) page, Risk Group Classification for Infectious Agents.

2.2.6 Risk Assessment
Biosafety Level classifications are appropriate for typical laboratory operations.  The Principal Investigator or laboratory director is responsible for implementing more (or less) stringent practices based on laboratory specific conditions.  Such a decision is ultimately the result a risk assessment process that accounts for the following:

  • Pathogenicity - the ability of an organism to cause disease.
  • Virulence - the severity of disease.
  • Transmission route - parenteral, ingestion, mucous membrane exposure, or inhalation. The latter route is of the greatest concern which is why organisms such as M. tuberculosis require more stringent control than organisms that are transmitted via direct contact, e.g., HBV.
  • Agent stability - survival in environment or otherwise prolonged viability (spore formation).
  • Infectious dose - the dose required to cause infection in humans or animals (ID 50 refers to the dose needed to infect 50% of the exposed population).
  • Antibiotic resistance.

The use of recombinant DNA may alter any of the above risk factors and investigators should take these modifications into consideration when working with recombinant microorganisms.

All of the above factors are inherent to a particular microbe; external factors to be considered in a risk assessment include:

  • Titer/volume of material used - titer may increase several orders of magnitude compared to levels in clinical samples, upon culturing.
  • Availability of effective treatment or vaccine.
  • Nature of activities - e.g., potential for splashes, volume used, complexity of manipulations, skills and training level of investigators.
  • Health status of investigator - e.g., immune state, pregnancy, vaccination status.

Go to Top