How a Class II Type A2 Biosafety Cabinet Works: Airflow, HEPA & Containment

By the Alpha Linear Engineering Team · Last updated 27 August 2026 · 7-min read

Quick answer: A Class II Type A2 biosafety cabinet works by combining two HEPA-filtered airstreams. Room air is drawn inward through the front opening at about 0.5 m/s (100 fpm), forming an air curtain that stops aerosols escaping. Inside, a blower recirculates roughly 70% of the air down onto the work surface through a downflow HEPA filter (protecting the sample), while about 30% is discharged through an exhaust HEPA filter (protecting the environment). This simultaneous inflow, downflow and filtered exhaust is what protects the operator, product and environment at once.

Key takeaways

  • Inflow at the face protects the operator; downflow protects the sample; HEPA exhaust protects the environment.
  • The A2 splits airflow ~70% recirculated / 30% exhausted.
  • A DC ECM motor holds velocities steady as the filter loads, extending filter life.
  • Genuine containment depends on those velocities staying in spec — which is why certification matters.

The airflow, step by step

  1. Inflow (air curtain). Room air is pulled in through the front grille at ~0.5 m/s. This inward barrier captures any aerosol that tries to escape the opening — this is your operator protection.
  2. Plenum split. Captured air joins the recirculating stream and is pushed by the blower into the pressurised plenum above the work zone.
  3. Downflow HEPA (~70%). About 70% of the air passes through the downflow HEPA and descends as clean, near-unidirectional air over the work surface — this is your product protection.
  4. Exhaust HEPA (~30%). The remaining ~30% is forced through the exhaust HEPA and released to the room or ducted out via a thimble — this is your environmental protection.
  5. Split point & balance. Downflow and inflow meet just above the work surface and are drawn into front and rear grilles, keeping the two protection zones separated.

→ Want the cutaway and full spec sheet? See how Alpha Linear engineers the Class II Type A2 — 11-part construction, H-14 HEPA and DC ECM motor.

What’s inside an Alpha Linear Class II Type A2

Component Function
Downflow HEPA filter (H-14) Delivers clean air over the work surface — 99.999% at 0.3 µm
Exhaust HEPA filter (H-14) Filters the ~30% discharged to room/duct
Constant-flow blower + DC ECM motor Maintains steady downflow/inflow as filters load
Stainless-steel work zone (SS 304/316) Single-sheet, easy-to-clean, chemical-resistant surface
10° sloped front sash Ergonomic reach, reduced glare, comfort over long sessions
Microcontroller + alarms Monitors airflow, sash position and filter status

Why the DC ECM motor matters

As a HEPA filter loads with particles over months of use, a fixed-speed AC motor lets airflow drift — degrading containment. A DC ECM motor automatically compensates to keep downflow and inflow velocities in spec, which maintains protection, extends filter life and cuts energy use. It’s a genuine build-quality differentiator worth checking on any quote.

How Type A2 differs from B2

The A2 recirculates ~70% of air; a Type B2 exhausts 100% for volatile-chemical and radionuclide work. If you only do microbiology or cell culture, the A2’s recirculating design is more efficient. New to the topic? Start with the biosafety cabinet guide or classes explained.

AL
Written by the Alpha Linear Engineering Team

Alpha Linear has designed, manufactured and validated biosafety cabinets and cleanroom systems since 1990 from its Peenya (Bangalore) facility. Our engineers are approved contractors for ISRO, HAL, IISc and BARC, and our BSCs run in 2,000+ labs including Biocon, ICAR-IVRI and Sami-Sabinsa. This article follows ISO 14644-1, NSF/ANSI 49, EN 12469 and the CDC-NIH BMBL.

Publishing tip: replace this with a named engineer + short bio and a “medically/technically reviewed by” line for maximum author-level EEAT.

Frequently asked questions

How does a Class II Type A2 biosafety cabinet work?

It draws room air inward at the front opening (~0.5 m/s) to protect the operator, recirculates about 70% of the air through a downflow HEPA filter onto the work surface to protect the sample, and exhausts about 30% through an exhaust HEPA filter to protect the environment. All three happen simultaneously.

What percentage of air does a Type A2 recirculate?

A Class II Type A2 biosafety cabinet recirculates approximately 70% of the work-zone air through a downflow HEPA filter and exhausts approximately 30% through an exhaust HEPA filter.

What is the inflow velocity of a Class II biosafety cabinet?

A Class II biosafety cabinet typically maintains a minimum average inflow (face) velocity of about 0.5 m/s (100 feet per minute), which creates the air curtain that protects the operator.

What does a HEPA filter do in a biosafety cabinet?

The HEPA filter removes at least 99.99% of particles at 0.3 microns, including aerosolised microorganisms. The downflow HEPA keeps the sample clean and the exhaust HEPA prevents contaminated air reaching the environment.

Ready to specify or certify your biosafety cabinet?

Alpha Linear designs, builds and validates BSCs from Bangalore — trusted by ISRO, BARC, Biocon and 2,000+ labs since 1990. Get a spec-matched quote or book certification.

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Also read

Sources & standards: NSF/ANSI 49; EN 12469; CDC-NIH BMBL; WHO Laboratory Biosafety Manual; ISO 14644-1; EN 1822; EN 61010-1:2010; EN 61326-1:2013; Alpha Linear product documentation.

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