Biosafety Level 2 (BSL-2)

Biosafety Level 2 (BSL-2) is the second of the four graded laboratory-containment tiers defined by the CDC/NIH publication Biosafety in Microbiological and Biomedical Laboratories (BMBL, 6th edition, 2020). A protocol is assigned BSL-2 when it involves agents that pose a moderate hazard to laboratory personnel and the environment, are generally treatable or preventable, and are transmitted primarily by direct or mucous-membrane contact, ingestion, or percutaneous exposure (e.g., a needlestick) rather than by inhalation of infectious aerosols. This page covers what BSL-2 specifically requires; for how BSL-2 relates to BSL-1, BSL-3, and BSL-4, and how a Biosafety Level is formally assigned, see the general Biosafety Level (BSL) entry — that context isn’t repeated here.

What makes a protocol BSL-2

BSL-2 is the default containment level for a large share of everyday microbiology, clinical, and diagnostic laboratory work. It is not defined by a single feature but by the combination of the agent’s Risk Group (most Risk Group 2 agents are handled at BSL-2, though an Institutional Biosafety Committee’s protocol-specific risk assessment can move a given protocol above or below that default), the practices followed, the personal protective equipment (PPE) used, and the facility’s engineering controls. Because most BSL-2 agents are not efficiently transmitted through the air, BSL-2 does not require the directional inward airflow, sealed penetrations, or double-door entry that BSL-3 requires — the added controls at BSL-2 instead target contact, ingestion, and sharps exposure.

Typical agents handled at BSL-2

Agents commonly assigned BSL-2 containment include hepatitis B virus (HBV), hepatitis A virus, HIV, herpes simplex virus, Staphylococcus aureus, Streptococcus pyogenes, Salmonella species and other common foodborne bacterial pathogens, and Toxoplasma gondii. BSL-2 is also the default containment for clinical and diagnostic work with human blood, body fluids, tissues, and primary cell lines whose infectious status is unknown — the source material is treated as though it may contain a bloodborne pathogen even when no specific agent has been identified. This is a representative, not exhaustive, list; the actual containment for any specific agent or clinical specimen is determined by an Institutional Biosafety Committee (IBC) risk assessment, not inferred from this list alone.

Required practices at BSL-2

BSL-2 builds on ordinary BSL-1 microbiological practice by adding controls aimed at limiting contact, ingestion, and sharps exposure:

• Restricted access. Access to the laboratory is limited to authorized personnel while work with BSL-2 agents is in progress.
• Biohazard signage. A biohazard warning sign is posted at the laboratory entrance whenever BSL-2 agents are in use, typically identifying the agent(s), the biosafety level, required immunizations, the responsible investigator’s contact information, and required PPE.
• Sharps precautions. Needles and other sharps are used only when there is no practical alternative, and mouth pipetting is prohibited.
• A written biosafety manual or standard operating procedures specific to the agents and procedures in use, which personnel are required to read and follow.
• Routine decontamination of work surfaces after use and at the end of each work session, and decontamination of laboratory waste before disposal.
• Occupational health measures appropriate to the agents handled — for example, hepatitis B vaccination offered to personnel with a reasonable expectation of exposure to human blood or other potentially infectious materials, consistent with OSHA’s Bloodborne Pathogens Standard (29 CFR 1910.1030), which applies independently of, and in addition to, BMBL/NIH biosafety requirements whenever a protocol involves human blood, tissue, or other potentially infectious materials.

Safety equipment and PPE at BSL-2

Any procedure that may generate an aerosol or splash — centrifugation, vortexing, sonication, or similar manipulations of an infectious agent — is performed inside a certified Class I or Class II biosafety cabinet (BSC) rather than on the open bench. Standard PPE at BSL-2 includes a lab coat or gown (buttoned or closed, and removed before leaving the laboratory) and gloves for any procedure involving contact with the agent or contaminated surfaces. Eye and face protection (safety glasses, goggles, or a face shield) is added for any manipulation performed outside a BSC where splashing or spraying is a realistic possibility.

Facility features required at BSL-2

Beyond BSL-1’s basic open-bench design, a BSL-2 facility is expected to have self-closing, lockable doors; a handwashing sink located near the point of exit; an eyewash station readily accessible within the laboratory; and access to equipment capable of decontaminating laboratory waste, such as an autoclave. Work surfaces are impervious to water and resistant to the chemicals used for routine decontamination.

Who assigns BSL-2, and how it’s reviewed

For research involving recombinant or synthetic nucleic acid molecules, the containment level — including BSL-2 — is formally assigned by an institution’s Institutional Biosafety Committee (IBC) under the NIH Guidelines, as part of a protocol registration and risk-assessment process, before laboratory work may begin. That process, IBC composition requirements, and how BSL relates to an agent’s underlying Risk Group are covered in full on the general Biosafety Level (BSL) page rather than repeated here. IBC review of laboratory biosafety is a separate compliance track from an Institutional Review Board (IRB)‘s review of human-subjects research ethics or a Scientific Review Committee‘s scientific-merit review — a single project involving, for example, a clinical specimen collection protocol can require sign-off from more than one of these committees, each reviewing a different dimension of the same work.

Worked examples

Example 1. A clinical microbiology laboratory that processes patient specimens — blood draws, wound swabs, urine and stool cultures — operates under BSL-2 as its default containment, because the infectious status of an incoming specimen is frequently unknown at the time it’s handled. Any step likely to aerosolize the specimen (vortexing a stool sample, for instance) is performed inside a certified biosafety cabinet, and personnel follow the lab’s IBC-approved biosafety manual and are offered hepatitis B vaccination under the lab’s OSHA bloodborne-pathogens exposure control plan.

Example 2. A university research lab studying Salmonella pathogenesis in a mouse model registers its protocol with the Institutional Biosafety Committee. The IBC’s risk assessment — accounting for the specific serovar, the route of animal inoculation, and the procedures used to process infected tissue — assigns BSL-2 containment, requiring restricted lab access during active work, BSC use for any aerosol-generating step (such as tissue homogenization), and documented decontamination of contaminated caging and waste before disposal.

Counter-example

A laboratory culturing Mycobacterium tuberculosis is not a BSL-2 example, even though tuberculosis is a well-known, treatable disease: because M. tuberculosis is transmitted efficiently by inhalation of infectious aerosols, the BMBL and most IBCs assign this work BSL-3 containment, which adds directional inward airflow, a controlled double-door entry, and mandatory use of biosafety cabinets for all agent manipulation — controls that go beyond what BSL-2 requires. Agent identity alone doesn’t determine the level; transmission route and the specific procedures involved do.

Related terms

• Biosafety Level (BSL) — the full four-tier system (BSL-1 through BSL-4) and how a level is assigned
• IRB (Institutional Review Board)
• Scientific Review Committee
• Laboratory Safety (OSHA Chemical Hygiene Plan) — the parallel OSHA framework for chemical, rather than biological, laboratory hazards

For the broader compliance context this term sits within, see the Integrity & Compliance cluster page.