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Biological Safety Cabinet Classes: I, II & III Explained

April 24, 2026August 17, 2026 Marketing Manager

Biological safety cabinets (BSCs) are the primary containment devices used in laboratories that work with infectious agents, cell cultures, and hazardous biological materials. Unlike chemical fume hoods, BSCs protect the researcher, the environment, AND the work product at the same time.

This guide explains what each biological safety cabinet class does, how the Class II types differ, what airflow rates you should expect at the front opening, and how to pick the right cabinet for your biosafety level. If you would rather talk it through, call (800) 326-4403 or see our biosafety cabinets for hospital and research labs.

Biological Safety Cabinet Classes at a Glance

There are three biological safety cabinet classes. The fastest way to tell them apart is to look at what each one protects.

Class II biological safety cabinets cover the large majority of lab work, which is why almost every buying question ends up being a question about Class II types.

What Does a Biological Safety Cabinet Do?

A BSC uses HEPA-filtered airflow to create three types of protection:

• Personnel protection: Inward airflow at the front opening prevents aerosols from escaping toward the researcher
• Product protection: HEPA-filtered downflow air creates a clean work zone that prevents airborne contamination of samples
• Environmental protection: Exhaust air passes through HEPA filters before being released, preventing biological agents from entering the building or outside environment

The U.S. reference for how these cabinets are used by biosafety level is the CDC and NIH publication Biosafety in Microbiological and Biomedical Laboratories (BMBL). Cabinet design and field certification requirements come from NSF/ANSI 49.

BSC Class I

Class I BSCs provide personnel and environmental protection only. They do NOT protect the work product.

• Airflow: Room air draws inward through the front opening, across the work surface, and out through a HEPA exhaust filter
• Protection: Personnel yes, product no, environment yes
• Applications: Low-risk work where product protection is not needed, such as handling diagnostic specimens or containing equipment that generates aerosols
• BSL rating: BSL-1, BSL-2

Class I cabinets are relatively rare in modern labs because Class II cabinets provide all the same protection plus product protection.

Class II Biological Safety Cabinets: Types A1, A2, B1 and B2

Class II BSCs are by far the most common type. They combine inward airflow at the front opening with HEPA-filtered vertical (downflow) air, so they protect the researcher, the product, and the environment. The types differ in how much air is recirculated, how the cabinet is connected to building exhaust, and whether volatile chemicals are allowed.

Browse our biological safety cabinet selection or compare models on our lab safety cabinet product pages.

Class II, Type A1

• Recirculates about 70% of the air and exhausts about 30% through HEPA
• Can exhaust back to the room or connect to building exhaust
• Minimum average inflow velocity of 75 fpm
• Used for BSL-1 through BSL-3 work with no volatile chemicals or radionuclides

Class II, Type A2 (Most Common)

• Recirculates about 70% of the air and exhausts about 30%
• Can be canopy connected to building exhaust when minute amounts of volatile chemicals are involved
• Minimum average inflow velocity of 100 fpm
• The default choice for microbiology, clinical specimen work and cell culture and PCR setups

Class II, Type B1

• Exhausts most of the contaminated downflow air and recirculates the balance
• Must be hard ducted to building exhaust
• Minimum average inflow velocity of 100 fpm
• Suitable for work with small amounts of volatile chemicals and trace radionuclides

Class II, Type B2 (Total Exhaust)

• 100% of the air is exhausted, with no recirculation
• Must be hard ducted to building exhaust
• Minimum average inflow velocity of 100 fpm
• Used when volatile chemicals or radionuclides are part of the biological work
• Highest exhaust and energy demand of the Class II types, so it drives HVAC design

Airflow Rates at the Front Access Opening of a Class II BSC

Inflow velocity is the speed of the room air pulled in through the front access opening. It is what keeps aerosols inside the cabinet instead of in the operator’s breathing zone.

Under NSF/ANSI 49, airflow rates into the front access opening of a Class II BSC fall in the 75 to 100 feet per minute range, measured as a minimum average:

• Class II Type A1: minimum average inflow of 75 fpm
• Class II Types A2, B1 and B2: minimum average inflow of 100 fpm
• Class I: commonly 75 fpm minimum at the opening
• Class III: not applicable, because the cabinet is sealed and has no open front

Two practical points. First, a manufacturer sets a nominal inflow for each model, and the certifier verifies the cabinet against that setpoint, not just against the floor value. Second, room conditions matter. Door swings, foot traffic, supply diffusers aimed at the sash and nearby fume hoods can disturb the air curtain even when the cabinet itself is working. Plan cabinet placement with your lab layout designer before the ductwork is set.

Airflow is verified during annual biological safety cabinet certification, after any move or repair, and after a filter change.

BSC Class III (Glove Box)

Class III cabinets are gas-tight, sealed enclosures with attached rubber gloves for handling materials inside. All air entering and leaving passes through HEPA filters, and material moves in and out through a pass-through box or dunk tank. They provide the highest level of protection and are used for BSL-4 maximum containment work.

• Protection: Maximum, with a physical sealed barrier between the researcher and the agents
• Applications: BSL-4 work and select agents that require absolute containment
• Planning note: Cost, room pressurization, and support systems are far beyond a Class II project, so these are designed facility first, cabinet second

Microbiological Safety Cabinet vs Biological Safety Cabinet

A microbiological safety cabinet (MSC) is the same equipment under a different name. MSC is the European term used with the EN 12469 standard, while biological safety cabinet is the North American term used with NSF/ANSI 49. If a specification, a paper or an imported cabinet uses the term microbiological safety cabinet, read it as a biological safety cabinet.

The two standards do not slice the categories the same way:

• EN 12469 covers Class I, Class II and Class III cabinets, and defines a single Class II category with no A1, A2, B1 or B2 subtypes.
• NSF/ANSI 49 covers Class II cabinets only and defines the subtypes, including the hard-ducted Type B2 total exhaust cabinet that EN 12469 has no direct equivalent for.

That matters when you buy. A cabinet listed to EN 12469 alone may not satisfy a U.S. specification that calls for an NSF/ANSI 49 listed Type A2 or B2. Ask for the listing before you order, not after.

Lab Safety Cabinet Terms People Mix Up

Searches for “lab safety cabinet” and “biological cabinet” land on four very different products. Here is how to keep them straight.

The clean bench mistake is the dangerous one. A horizontal clean bench looks similar to a Class II cabinet but pushes air at the operator, so it must never be used with infectious material or hazardous drugs. See our biosafety cabinet vs fume hood comparison for a longer breakdown.

How to Choose a Biological Safety Cabinet in 5 Steps

1. Confirm your biosafety level and agents. Your institutional biosafety committee or risk assessment sets BSL-1 through BSL-4. That decides Class I, Class II or Class III.
2. Decide if the sample needs protection. If sterility matters, you need Class II, not Class I.
3. List every chemical used inside the cabinet. No volatiles points to Type A2. Small amounts point to a canopy connected A2 or a Type B1. Routine volatile or radionuclide work points to Type B2.
4. Check the building. Hard-ducted B1 and B2 cabinets need dedicated exhaust, a fan, a monitored connection and HVAC capacity. Confirm that before you pick a model, since ductwork often costs more than the change in cabinet price.
5. Size the cabinet to the bench and the room. Common widths are 3, 4, 5 and 6 feet. Confirm the door path, ceiling height and service clearances, then set the working height for seated or standing use.

Need a second opinion on step 3 or 4? Call (800) 326-4403 and we will review your agents, chemicals and exhaust options with you.

Quick Selection Guide

What Drives Biological Safety Cabinet Cost

Published price ranges for biosafety cabinets are not reliable, because two cabinets of the same width can differ by thousands of dollars once exhaust and controls are included. Use these cost drivers instead, then ask for a quote on your actual configuration.

For a current number on your exact class, type, width and exhaust setup, request a quote through our biosafety cabinet product page or call (800) 326-4403.

BSC vs. Fume Hood: Key Differences

The most common mistake in lab safety is using a fume hood when a BSC is needed, or the reverse:

• Fume hoods protect the USER from chemical fumes. They do NOT provide product protection or biological containment.
• BSCs protect the USER, the PRODUCT, and the ENVIRONMENT from biological hazards. They are NOT designed for large-volume chemical use.

Read our detailed comparison: Biological Safety Cabinet vs. Fume Hood

Frequently Asked Questions

What are the three classes of biological safety cabinets?

Class I protects personnel and the environment but not the sample. Class II protects personnel, the sample and the environment, and is split into Types A1, A2, B1, B2 and C1. Class III is a sealed glove box for maximum containment work.

What airflow rate is required at the front access opening of a Class II BSC?

NSF/ANSI 49 sets a minimum average inflow velocity of 75 fpm for Class II Type A1 and 100 fpm for Types A2, B1 and B2, so the answer to the common exam question is the 75 to 100 feet per minute range. Certifiers verify inflow against the manufacturer setpoint for the specific model.

Which biosafety cabinet class is most common?

Class II Type A2. It gives personnel, product and environmental protection, works for BSL-1 through BSL-3 agents, and can be canopy connected if minute amounts of volatile chemicals are used.

How much does a biological safety cabinet cost?

Price depends on class and type, cabinet width, exhaust connection, base stand and accessories, installation and initial certification. Hard-ducted B1 and B2 cabinets carry both a higher cabinet price and separate ductwork costs. Ask for a quote on your exact configuration rather than a list price.

Is a microbiological safety cabinet the same as a biosafety cabinet?

Yes. Microbiological safety cabinet is the European term tied to EN 12469, and biological safety cabinet is the North American term tied to NSF/ANSI 49. Check which standard your specification requires, since EN 12469 does not define the NSF Class II subtypes.

How often should BSCs be certified?

Annually, and again after any move, repair, or filter change. NSF/ANSI 49 requires field certification by a qualified technician using standardized test protocols.

Can I use a BSC as a fume hood?

No. BSCs are not designed to handle volatile chemical fumes. Using a BSC as a chemical fume hood can damage the HEPA filters and compromise containment. Use a chemistry fume hood for chemical work.

Can a Class II cabinet be moved to another room?

Yes, but it must be decontaminated before the move and recertified in the new location before use. See our guide to biological safety cabinet decontamination.

Get Expert BSC Selection Help

Not sure which BSC class and type you need? Our lab safety specialists will review your agents, protocols, chemicals and lab ventilation and recommend the right cabinet.

Request a free BSC consultation or call (800) 326-4403.