Laboratory biosafety describes the application of specific practices, safety equipment and specially designed laboratories to create a safe environment, both within and outside the laboratory, for work conducted with infectious agents and toxins. In addition, there is monitoring for occupationally acquired infections and staff training, as appropriate.
“Biosafety Levels” (BSLs) are designations applied to projects or activities conducted in laboratories in ascending order of containment based on the degree of the health-related risk associated with the work being conducted. In the United States, the designations BSL-1, BSL-2, BSL-3, and BSL-4 describe the minimum safe work practices, specially designed buildings, and safety equipment required to conduct work on infectious microorganisms and other biological hazards. BSL-4 is the highest biosafety level.
The appropriate BSL for a project is determined jointly by the principal investigator, the institutional biosafety professionals and biosafety committees. The BSL assigned to a project is based on a biological risk assessment that takes into account:
The nature of the infectious agent, toxin, or other biological hazard, including:
- Its ability to cause disease and the way(s) in which it causes disease (transmissibility and pathogenicity);
- How much of it is required to cause disease (infectious dose);
- How many different organisms are susceptible to infection (host range); and
- Its prevalence in the community (epidemiology);
- The specific laboratory activity or activities being performed; and
- The availability of preventive medical countermeasures (i.e., vaccines) or effective treatment (i.e., post-exposure vaccination and/or use of antimicrobials, antivirals and chemotherapeutic agents).
The BSL assigned to a project determines the controls required to conduct the work safely:
- Engineering controls, including facility construction and design elements in the laboratory space;
Safety equipment, including personal protective equipment (PPE) and biosafety cabinets;
Administrative controls, including specific access, training, and occupational medicine policies; and
- Laboratory practices and procedures workers use when working in the laboratory.
Every biological laboratory, regardless of biosafety level, follows standard microbiological practices. Each biosafety level builds on the controls of the next lower level. Each biosafety level has its own specific containment controls. The assignment of a biosafety level to a particular work process is made through a protocol driven risk assessment.
For more information on other aspects of the biosafety levels, please see the rest of the biosafety section for a general overview.
Laboratory Containment for Human Pathogens:
Biosafety Level 1 – Biosafety Level 4 facilities
Biosafety Level 1 (BSL-1)
BSL-1 labs are used to study infectious agents or toxins not known to consistently cause disease in healthy adult humans or animals. Workers follow basic safety procedures, called standard microbial practices, and require no special equipment or design features. Standard engineering controls in BSL-1 laboratories include easily cleaned surfaces that are able to withstand the basic chemicals used in the laboratory.
Specific considerations for a BSL-1 laboratory include the following:
- Standard microbiological practices are followed.
- Work can be performed on an open lab bench or table.
- PPE (lab coats, gloves, eye protection) are worn.
- A sink must be available for hand washing.
- The lab should have doors to separate the working space with the rest of the facility.
Biosafety Level 2 (BSL-2)
BSL-2 laboratories are used to study moderate-risk infectious agents or toxins that pose a moderate danger if accidentally inhaled, swallowed, or exposed to the skin. Design requirements for BSL-2 laboratories include hand washing sinks, eye washing stations, and doors that close and lock automatically. BSL-2 laboratories must also have access to equipment that can decontaminate laboratory waste, including an incinerator, an autoclave, and/or another method of decontamination, depending on the biological risk assessment.
In addition to BSL-1 considerations, BSL-2 laboratories have the following containment requirements:
- Access to the laboratory is restricted when work is being conducted.
- Appropriate PPE is worn, including lab coats and gloves, eye protection and face shields.
- All procedures that can cause infection from aerosols or splashes are performed within a biological safety cabinet (BSC).
- An autoclave or an alternative method of decontamination is available.
- The laboratory has self-closing doors.
- A sink and eyewash are readily available.
Biosafety Level 3 (BSL-3)
BSL-3 laboratories are used to study infectious agents or toxins that may be transmitted through the air and cause potentially lethal infections. Researchers perform all experiments in a biosafety cabinet. BSL-3 laboratories are designed to be easily decontaminated. As an additional safety measure, these laboratories must use controlled, or “directional,” air flow to ensure that air flows from non-laboratory areas (such as the hallway) into laboratory areas.
Other engineered safety features include a requirement for entry through two self-closing, interlocked doors, sealed windows, floors and walls, and filtered ventilation systems. BSL-3 labs must also be equipped to decontaminate laboratory waste using an incinerator, an autoclave, and/or another method of decontamination, depending on the biological risk assessment.
In addition to BSL-2 considerations, BSL-3 laboratories have the following containment requirements:
- An Occupational Health Program exists for medical surveillance of laboratory workers. Laboratory workers are under medical surveillance and may be offered immunizations for infectious agents or toxins they work with, if available.
- Access to the laboratory is restricted and controlled at all times.
- Appropriate PPE must be worn, and respirators might be required.
- All work with infectious agents or toxins must be performed within an appropriate biosafety cabinet.
- 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 self-closing and interlocked doors.
Biosafety Level 4 (BSL-4)
BSL-4 laboratories are used to study infectious agents or toxins that pose a high risk of aerosol-transmitted laboratory infections and life-threatening disease for which no vaccines or therapies are available. The laboratories incorporate all BSL-3 features, as well as, additional safety features. Access to BSL-4 laboratories is carefully controlled and requires significant training.
There are two types of BSL-4 laboratories:
Cabinet laboratory – all work with infectious agents or toxins is done in a Class III Biosafety Cabinet with very carefully designed procedures to contain any potential contamination. In addition, the laboratory space is designed to also prevent contamination of other spaces.
Suit laboratory – Laboratory personnel are required to wear full-body, air-supplied suits, which are the most sophisticated type of PPE. All personnel shower before exiting the laboratory and go through a series of procedures designed to fully decontaminate them before leaving.
While the engineering controls required for BSL-4 cabinet and BSL-4 suit laboratories differ in some respects, the controls are extensive and supplemented by carefully designed procedures and practices in both types of laboratories.
In addition to BSL-3 considerations, BSL-4 laboratories have the following containment requirements (this list is not exhaustive):
- Change clothing before entering.
- Shower upon exiting.
- Decontaminate all materials before exiting.
- All work with infectious agents or toxins must be performed within a certified biosafety cabinet, for work performed in the cabinet laboratory, or while wearing a full body, air-supplied, positive pressure suit.
- 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.
For a tour of a BSL-4 laboratory, please see the NIH website.