Key takeaways
- The class is set by what you protect and how dangerous the agent is.
- Only Class II and III protect the product; Class I does not.
- Class II Type A2 is the default for the vast majority of labs.
- Class III is a physical-containment glovebox for BSL-4 agents.
Class I biosafety cabinet
A Class I BSC draws unfiltered room air inward across the work opening — protecting the operator — and exhausts it through a HEPA filter, protecting the environment. Because the incoming air is not filtered, the sample is not protected from contamination. Class I cabinets suit low-to-moderate risk agents where product sterility doesn’t matter, or to enclose aerosol-generating equipment such as centrifuges.
Class II biosafety cabinet (the workhorse)
A Class II BSC adds a HEPA-filtered downflow of clean air over the work surface, so it protects the operator, sample and environment simultaneously. This is why Class II accounts for the overwhelming majority of cabinets in microbiology, cell culture, diagnostics and pharmaceutical labs. It splits into four subtypes by recirculation and ducting:
- Type A1 — ~70% recirculated; may exhaust to room; not for volatile chemicals.
- Type A2 — ~70% recirculated; room or thimble-ducted; trace volatile chemicals if ducted. The most common cabinet.
- Type B1 — ~70% exhausted; hard-ducted; moderate volatile chemicals.
- Type B2 — 100% exhausted (total exhaust); for volatile chemicals and radionuclides.
Choosing between the common two? See A2 vs B2 compared.
→ Most labs need a Class II Type A2. See Alpha Linear’s Class II biosafety cabinet range and specifications.
Class III biosafety cabinet
A Class III BSC is a totally enclosed, gas-tight, welded glovebox operated through sealed glove ports. It maintains negative pressure relative to the room, supplies HEPA-filtered air and exhausts through two HEPA filters in series (optionally with UV sterilisation), giving 100% physical containment for the most dangerous agents — typically BSL-4. Materials pass in and out through an integrated, mechanically interlocked pass box. Alpha Linear’s Class III cabinet is a fully welded enclosure with an integrated dynamic pass box for safe material transfer.
How HEPA filter grades work
Every class relies on HEPA (High-Efficiency Particulate Air) filters. Under EN 1822, grades run H-13, H-14 (HEPA) and U-15+ (ULPA). Alpha Linear uses H-14 grade HEPA (99.999% at 0.3 microns) as standard, with ULPA available for the most critical aseptic work. HEPA capture is most challenging at the most penetrating particle size (~0.3 µm), which is exactly where these grades are rated.
Biosafety cabinet selection chart
| If you need… | Choose |
|---|---|
| Operator + environment protection, product sterility not required | Class I |
| Operator + product + environment protection, BSL-1 to BSL-3 | Class II Type A2 |
| The above, plus regular volatile toxic chemicals / radionuclides | Class II Type B2 |
| Maximum containment for BSL-4 / most dangerous agents | Class III |
| Product protection only, no biohazard | Laminar air flow (not a BSC) |
That last row is the most common purchasing mistake — see biosafety cabinet vs laminar air flow. For the full picture, return to the biosafety cabinet guide.
Frequently asked questions
What are the 3 classes of biosafety cabinets?
Class I protects personnel and environment but not the sample. Class II protects personnel, sample and environment and is the most common class (subtypes A1, A2, B1, B2). Class III is a sealed, gas-tight glovebox that provides maximum containment for the most dangerous agents.
What is the most commonly used biosafety cabinet?
The Class II Type A2 is the most commonly used biosafety cabinet. It protects the operator, sample and environment, recirculates about 70% of air through a downflow HEPA filter, and suits BSL-1 to BSL-3 microbiology, cell culture and diagnostics.
What is the difference between Class I and Class II?
Class I filters only the exhaust air, so it protects the operator and environment but not the sample. Class II also blows HEPA-filtered air down over the work surface, so it additionally protects the sample from contamination.
When do you need a Class III biosafety cabinet?
A Class III cabinet is used for the most dangerous, high-risk agents — typically BSL-4 pathogens. It is a gas-tight glovebox operated through sealed glove ports under negative pressure, giving 100% physical containment.
Alpha Linear designs, builds and certifies BSCs from Bangalore — trusted by ISRO, BARC, Biocon and 2,000+ labs since 1990. Get a spec-matched quote today.
Sources & standards: NSF/ANSI 49; EN 12469; CDC-NIH BMBL; WHO Laboratory Biosafety Manual; ISO 14644-1; EN 1822; Alpha Linear product documentation.
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