Biohazard and Biosafety level

Biohazard and biosafety

A very specialized research laboratory that deals with infectious agents is the biosafety lab. Protection for laboratory personnel, the environment, and the local community must be considered and ensured. Biohazard levels, more commonly referred to as “biological safety levels” or “biosafety levels,” are classifications of safety precautions necessary to be applied in the clinical microbiology laboratory depending on specific pathogens handled when performing laboratory procedures. 

At any given biosafety level, there will be strict requirements for laboratory design, personal protective equipment, and biosafety equipment to be used. Standard Microbiological Practices are required at all biosafety levels and are good practice for experiments below the BSL-1 threshold. 

There is a classification of infective microorganisms by risk groups, particular microorganism may be handled in particular biosafety levels. Hence, the classification of infective microorganisms are given below (WHO).

Risk Group 1: A microorganism that is unlikely to cause human or animal disease.

Risk Group 2: A pathogen that can cause human or animal disease but is unlikely to be a serious hazard to laboratory workers, the community, livestock or the environment. Laboratory exposures may cause serious infection, but effective treatment and preventive measures are available and he risk of spread of infection is limited.

Risk Group 3: A pathogen that usually causes serious human or animal disease but does not ordinarily spread from one infected individual to another. Effective treatment and preventive measures are available.

Risk Group 4: A pathogen that usually causes serious human or animal disease and that can be readily transmitted from one individual to another, directly or indirectly. Effective treatment and preventive measures are not usually available.

Activities and projects conducted in biological laboratories are categorized by biosafety level. The four biosafety levels are BSL-1, BSL-2, BSL-3, and BSL-4, with BSL-4 being the highest (maximum) level of containment. There are additional specific rules and designations for animal research (ABSL), agricultural research (BSL-Ag), and other types of research.

The classification of biosafety levels are given below:

Biosafety Level 1 (BSL-1): Biosafety level one, the lowest level, applies to work with agents that usually pose a minimal potential threat to laboratory workers and the environment and do not consistently cause disease in healthy adults. BSL-1 labs are used to study infectious agents or toxins not known to consistently cause disease in healthy adults. They follow basic safety procedures, called Standard Microbiological 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. These include mechanical pipetting only (no mouth pipetting allowed), safe sharps handeling, avoidance of splashes or aerosols, and decontamination of all work surfaces when work is complete, e.g., daily.

Biosafety Level 2 (BSL-2): BSL-2 laboratories are used to study moderate-risk infectious agents or toxins that pose a risk if accidentally inhaled, swallowed, or exposed to the skin. Biosafety level two would cover work with agents associated with human disease, in other words, pathogenic or infectious organisms posing a moderate hazard. Examples are the equine encephalitis viruses and HIV when performing routine diagnostic procedures or work with clinical specimens. Therefore, because of their potential to cause human disease, great care is used to prevent percutaneous injury (needlesticks, cuts and other breaches of the skin), ingestion and mucous membrane exposures in addition to the standard microbiological practices of BSL 1. Design requirements for BSL-2 laboratories include hand washing sinks, eye washing stations in case of accidents, and doors that close automatically and lock. BSL-2 labs must also have access to equipment that can decontaminate laboratory waste, including an incinerator, an autoclave, and/or another method, depending on the biological risk assessment.

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 infection through inhalation exposure. Yellow fever, St. Louis encephalitis and West Nile virus are examples of agents requiring biosafety level 3 practices and containment. Work with these agents is strictly controlled and must be registered with all appropriate government agencies. These are indigenous or exotic agents that may cause serious or lethal disease via aerosol transmission, i.e., simple inhalation of particles or droplets.  Facility design should incorporate self-closing double-door access separated from general building corridors. The ventilation must provide ducted, directional airflow by drawing air into the lab from clean areas and with no recirculation.

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 vaccine or therapy is available. Examples are the Ebola virus, the Lassa virus, and any agent with unknown risks of pathogenicity and transmission. These facilities provide the maximum protection and containment. Usually, BSL 4 laboratories are in separate buildings or a totally isolated zone with dedicated supply and exhaust ventilation. Exhaust streams are filtered through high-efficiency particulate air (HEPA) filters, depending on the agents used.


  1. Bayot ML, King KC. Biohazard Levels. [Updated 2020 Sep 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan
  3. Biennial Review of the Lists of Select Agents and Toxins, National Select Agent Registry, CDC. Atlanta, GA. 2010.
  • Resource: Laboratory Biosafety Manual 2004; Page 1 World Health Organization 
  • Biosafety in Microbiological and Biomedical Laboratories, 5th edition, Centers for Disease Control and Prevention and National Institutes of Health, February 2007.