Biological Safety Cabinets: Class I, II & III Explained

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 simultaneously.

Understanding the differences between BSC classes is essential for selecting the right cabinet for your biosafety level and experimental requirements. Here’s a complete breakdown.

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

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 ✅ | Product ❌ | Environment ✅
• Applications: Low-risk work where product protection isn’t needed, such as handling diagnostic specimens or mixing hazardous drugs
• 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.

BSC Class II

Class II BSCs are by far the most common type, providing all three types of protection. They use a combination of inward airflow and HEPA-filtered vertical (downflow) air to protect the researcher, the product, and the environment.

Browse our biological safety cabinet selection →

Class II, Type A1

• Recirculates 70% of air, exhausts 30% through HEPA
• Can recirculate back to the room or connect to exhaust ductwork
• Minimum inflow: 75 fpm
• Suitable for BSL-1 through BSL-3
• Not for: Volatile chemicals or radionuclides

Class II, Type A2 (Most Popular)

• Recirculates 70% of air, exhausts 30%
• Can be canopy-connected to exhaust ductwork for volatile chemical use
• Minimum inflow: 100 fpm
• Suitable for BSL-1 through BSL-3
• Most versatile: Works for microbiology, cell culture, and minute quantities of volatile chemicals when ducted

Class II, Type B1

• Exhausts 70% of air through HEPA, recirculates 30%
• Must be hard-ducted to building exhaust
• Minimum inflow: 100 fpm
• Suitable for work with small quantities of volatile chemicals and radionuclides

Class II, Type B2 (Total Exhaust)

• 100% of air is exhausted — no recirculation
• Must be hard-ducted to building exhaust
• Minimum inflow: 100 fpm
• Required for work with larger quantities of volatile chemicals and radionuclides
• Highest energy consumption of all Class II types

BSC Class III (Glove Box)

Class III cabinets are gas-tight, sealed enclosures with attached rubber gloves for manipulating materials inside. All air entering and leaving passes through HEPA filters. They provide the highest level of protection and are required for BSL-4 (maximum containment) work.

• Protection: Maximum — gas-tight barrier between researcher and agents
• Applications: BSL-4 work, extremely dangerous pathogens (Ebola, Marburg)
• Cost: Significantly higher than Class II ($25,000–$80,000+)

Quick Selection Guide

Your Application	Recommended BSC
Cell culture, microbiology, PCR	Class II, Type A2
Diagnostic specimen handling	Class II, Type A2
Minute volatile chemical + bio work	Class II, Type A2 (ducted)
Small-quantity volatile/radionuclide	Class II, Type B1
Larger volatile chemical + bio work	Class II, Type B2
BSL-4 maximum containment	Class III

BSC vs. Fume Hood: Key Differences

The most common mistake in lab safety is using a fume hood when a BSC is needed (or vice versa):

• 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

How much does a biological safety cabinet cost?

Class II, Type A2 BSCs range from $5,000–$15,000 depending on size and features. Type B1 and B2 cost more ($10,000–$25,000) due to harder ductwork requirements. Installation adds $2,000–$8,000.

How often should BSCs be certified?

Annually, or 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.

Get Expert BSC Selection Help

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

Request a free BSC consultation → or call (801) 999-8277.