Biohazard Levels: BSL-1 to BSL-4, Risk Groups and Cleanup

You are probably looking for one of three systems

The phrase biohazard level does not appear in the BMBL, the NIH Guidelines or the WHO manual. Like biohazard safety level, it is how people search for three different numbered systems, and restoration searchers in particular tend to land on laboratory pages while looking for cleanup rules. Start with the row that matches your question.

If your question is about	You want	Who publishes it	Numbered as
How a laboratory is built and run	Biosafety levels (BSL)	CDC and NIH, BMBL 6th edition	BSL-1 to BSL-4
Lab work with infected animals	Animal biosafety levels (ABSL)	CDC and NIH, BMBL Section V	ABSL-1 to ABSL-4
How dangerous a specific organism is	Risk groups (RG)	NIH Guidelines Appendix B; WHO	RG1 to RG4
Cleaning blood or body fluids from a property	OSHA Bloodborne Pathogens; ANSI/IICRC S540	OSHA; IICRC	No levels
Sewage in a building	IICRC water categories	IICRC S500	Category 1 to 3
Who may do trauma cleanup in a state	State registration law	For example CDPH (California), Secretary of State (Georgia)	No levels

Sewage has its own numbered scheme, the three IICRC water categories, explained on our water categories page. It is unrelated to biosafety levels.

The four biosafety levels, side by side

The BMBL 6th edition is the reference. Its Section IV sets standard microbiological practices, special practices, safety equipment (primary barriers) and facility design (secondary barriers) for each level, and the CDC Quick Learn on biosafety levels puts the principle in one line: each level builds on the controls of the level before it. The table uses BMBL’s own agent examples.

Level	Agents it suits (BMBL wording, condensed)	BMBL examples	What changes at this level
BSL-1	Well-characterised agents not known to consistently cause illness in healthy adults	Bacillus subtilis, Naegleria gruberi, infectious canine hepatitis virus	Standard practices; door, handwashing sink, cleanable benches. No special barriers.
BSL-2	Agents linked to human illness of varying severity, moderate hazard	Hepatitis B virus, HIV, Salmonella, Toxoplasma	Restricted access during work; trained, supervised staff; splash or aerosol work in a biosafety cabinet (BSC).
BSL-3	Agents with potential for respiratory transmission that may cause serious or potentially lethal infection	Mycobacterium tuberculosis, St. Louis encephalitis virus, Coxiella burnetii	All infectious work in a BSC; two self-closing doors; sealed surfaces; ducted inward airflow.
BSL-4	Dangerous, exotic agents with high individual risk by aerosol and no available vaccine or therapy	Marburg virus, Congo-Crimean hemorrhagic fever virus	Class III cabinet or positive-pressure suit; exit shower; separate building or isolated zone.

One way to see the step up is to count. Section IV lists its requirements as numbered items under four headings. Counting the top-level items gives 28 at BSL-1, 38 at BSL-2 and 47 at BSL-3, then 57 for a BSL-4 cabinet lab and 55 for a suit lab. The count is ours and blunt: one item can be a sentence or a page. The direction is the point.

Biohazard level 2 (BSL-2) in detail

Biohazard level 2 is the most searched level, and the one that touches restoration work most. The BMBL 6th edition says BSL-2 differs from BSL-1 in three ways: staff receive specific training and are supervised by competent scientists, access is restricted while work is under way, and any procedure that may create infectious aerosols or splashes is done in a BSC or other containment equipment.

BMBL also notes that work with human-derived specimens such as blood, body fluids and tissues, where an agent may be present but unknown, can often be done safely under conditions typically associated with BSL-2, and it tells staff handling human material to refer to the OSHA Bloodborne Pathogens standard. That sentence is the bridge between the lab world and a trauma scene. In a building, the rule that applies to blood is the OSHA standard, not a lab level.

BSL-2 element	What BMBL Section IV says
Entry sign	A sign with the universal biohazard symbol at the entrance when infectious materials are present, naming the biosafety level, a responsible person and PPE requirements
Waste	A method for decontaminating all laboratory waste is available, such as autoclave, chemical disinfection or incineration
Doors and sink	Self-closing, lockable doors; a handwashing sink near the exit
Eyewash	Readily available in the laboratory
Cabinets	BSC performance checked at least annually
Ventilation	No specific requirement; new builds consider inward airflow without recirculation

BSL-3 and BSL-4: containment becomes the building

At BSL-3 the BMBL 6th edition moves the protection into the building. Access is through two consecutive self-closing doors, the handwashing sink is hands-free, floors, walls and ceilings are sealed for decontamination, windows are sealed, and a ducted ventilation system draws air from clean toward potentially contaminated areas, designed so the flow will not reverse at the containment barrier on failure. No work with open vessels happens on the bench.

BSL-4 comes in two models. In a cabinet laboratory, agents are handled in a Class III BSC; in a suit laboratory, staff wear a positive-pressure supplied-air suit. Everyone leaving takes a personal body shower, suit-lab staff pass a chemical shower first, and the facility may be a separate building or an isolated zone. A Class III cabinet takes supply air through a HEPA filter and exhausts through two in series. The nearest restoration analogue is negative air with HEPA filtration, covered on our air scrubber page, but no cleanup standard borrows the BSL label.

Animal biosafety levels

Section V of the BMBL 6th edition sets four animal biosafety levels for work with infected laboratory animals, plus ABSL-3Ag for certain agriculture work. Each builds on the one below, as BSLs do.

Level	BMBL summary
ABSL-1	Well-characterised agents not known to consistently cause illness in healthy adults; minimal hazard
ABSL-2	Agents linked to human illness, moderate hazard; a BSC for procedures that may create aerosols or splashes
ABSL-3	Aerosol potential and serious or potentially lethal outcomes; all procedures in BSCs, inward airflow, hands-free sinks
ABSL-4	Dangerous, exotic agents; Class III cabinet or positive-pressure suit facility with HEPA supply and exhaust

Risk groups are not biosafety levels

Risk groups classify organisms; biosafety levels classify the room and the work. The BMBL 6th edition is blunt: its four levels are not to be confused and equated with agent risk groups, and an agent listed in Risk Group 3 does not mean the work must happen in a BSL-3 lab. Risk group is one input to a risk assessment that also weighs the procedure, the quantity and the people.

Group	NIH Guidelines (April 2024)	WHO classical definition
RG1	Not associated with illness in healthy adult humans	No or low individual and community risk
RG2	Associated with human illness that is rarely serious; interventions often available	Moderate individual risk, low community risk
RG3	Serious or lethal human illness; interventions may be available	High individual risk, low community risk
RG4	Likely to cause serious or lethal human illness; interventions not usually available	High individual and community risk

WHO went further. The WHO Laboratory Biosafety Manual, 4th edition, published 21 December 2020, says earlier editions’ risk group and biosafety level framing led to the misconception that an agent’s risk group directly corresponds to a laboratory’s level. It replaces the tiers with core requirements, heightened control measures and maximum containment measures, the last described as what used to be called BSL-4. The NIH list is also not exhaustive: agents missing from Risk Groups 2 to 4 are not automatically Risk Group 1.

How many labs run at the top levels

Few labs work at the top. One federal source splits labs by level for the entities it registers: the Federal Select Agent Program 2024 report reports 230 registered entities in 2024, of which 77% had BSL-3 or ABSL-3 labs, 28% had BSL-2 or ABSL-2 labs and 3% had BSL-4 or ABSL-4 labs. Three percent of 230 is about 7 entities.

How property biohazard cleanup is classified instead

Property cleanup has no levels. The governing rule for crews is 29 CFR 1910.1030, which applies to occupational exposure to blood or other potentially infectious materials and contains no tiers; its only lab-specific part, paragraph (e), covers HIV and HBV research laboratories and production facilities. The industry standard is ANSI/IICRC S540, the Standard for Trauma and Crime Scene Cleanup, second edition, 2023, which IICRC says covers procedures regardless of surface, item or location and assumes the scene has been released.

Framework	What it classifies	Force
OSHA 29 CFR 1910.1030	Blood, OPIM, sharps and regulated waste an employee may contact	Federal regulation for employers
ANSI/IICRC S540 (2023)	Inspection, work plans and procedures for trauma and crime scenes	Consensus standard
IICRC S500 categories	Water by contamination; sewage is Category 3	Consensus standard
California Trauma Scene Waste Management Act	Who may remove trauma scene waste commercially	State law, CDPH registration
Georgia, Chapter 46A of Title 43	Who may clean trauma scenes commercially	State law, Secretary of State registration

Two states show what registration looks like. California’s Act, in the CDPH compilation, covers anyone who removes blood, body fluids and residues from a serious injury, illness or death scene as a business. Georgia’s Georgia HB 417 (2020), effective 1 January 2021, covers homicide, suicide and deaths with advanced decomposition, and excludes motor vehicle accidents and OSHA-regulated workplaces.

Requirement	California	Georgia
Registers with	Department of Public Health	Secretary of State
Fee	$200 a year (2017 compilation)	$100, valid 3 years, renewable
Background check	None in Chapter 9.5	Fingerprint check before registering and every 3 years
Bond or insurance	None in Chapter 9.5	$25,000 bond; $100,000 liability per occurrence
Waste handling	Removed at end of removal phase; freezer storage up to 14 days	Defined as potentially infectious material or regulated biomedical waste
Local control	CDPH is the sole enforcement agency	Counties and cities may not require their own

Cost and how to check a firm are on our biohazard cleanup guide; sewage jobs are on our sewage damage cleanup guide; careers on our biohazard cleanup jobs page.

For contractors: the words to use on a scope

A short checklist keeps the paperwork honest. Each line has a reason an adjuster or client will recognise.

1. Do not write BSL on an estimate. BSLs describe laboratories. Name the framework instead: OSHA 1910.1030 controls, S540 procedures, S500 Category 3.
2. Describe the material. Blood, OPIM, sharps or Category 3 water, in the regulation’s own terms.
3. Cite the state. Note California CDPH or Georgia Secretary of State registration where it applies.
4. Show the waste route. Hauler, facility and manifest belong in the file.
5. Keep lab language for lab losses. Water damage inside a BSL-3 suite is a different job; BMBL has the laboratory supervisor enforce access under institutional policy.

Questions people actually ask

What is the difference between biosafety levels 1, 2, 3 and 4?

Each level adds controls to the last. BSL-1 relies on standard practices and a basic lab. BSL-2 adds trained, supervised staff, restricted access and cabinets for splash work. BSL-3 adds two-door entry, sealed surfaces and inward airflow. BSL-4 adds Class III cabinets or positive-pressure suits, exit showers and an isolated building or zone, per the CDC and NIH BMBL.

What is a level 3 biohazard?

Usually the searcher means BSL-3, the containment level BMBL sets for agents with a potential for respiratory transmission that may cause serious or potentially lethal infection, such as Mycobacterium tuberculosis. All infectious work happens in a biosafety cabinet, behind two self-closing doors, with ducted airflow drawn inward. It is a lab design, not a cleanup grade.

What are level 4 biohazards?

BMBL reserves BSL-4 for dangerous and exotic agents that pose a high individual risk by aerosol and have no available vaccine or therapy, naming Marburg virus and Congo-Crimean hemorrhagic fever virus as examples. Work happens in a Class III cabinet or a positive-pressure suit. The Federal Select Agent Program reports that 3% of its 230 registered entities had BSL-4 or ABSL-4 labs in 2024.

What are risk groups 1, 2, 3 and 4?

Risk groups rank organisms, not labs. The NIH Guidelines define RG1 agents as not associated with illness in healthy adults, rising to RG4 agents likely to cause serious or lethal illness with no usual interventions. BMBL warns that risk groups must not be equated with biosafety levels, and WHO’s 2020 manual moved away from that shortcut.

Is there a biosafety level 5?

No. The CDC and NIH BMBL, 6th edition, defines four biosafety levels, BSL-1 to BSL-4, plus four animal levels and an agriculture variant, ABSL-3Ag. WHO’s 2020 manual describes maximum containment measures as its top tier, matching what was called BSL-4. Any level 5 seen online is not drawn from either document.

Is biohazard cleanup rated by level?

No. OSHA’s 29 CFR 1910.1030 governs worker protection on blood and body fluid work without tiers, ANSI/IICRC S540 sets trauma scene procedures, and sewage uses IICRC water categories. States such as California and Georgia add registration for commercial trauma cleaners. A firm quoting a level 2 cleanup is using marketing language, not citing a regulatory class.