Laminar flow hoods: what a laminar flow hood protects, horizontal against vertical and when a vertical laminar flow hood is the right one, and when you need a biosafety cabinet instead

Choosing the geometry

1. Horizontal flow blows toward the operator. Air passes through the filter at the back and travels across the work surface toward you. Product protection is excellent and there is no barrier between the work and your face, so it suits media plating, electronics and sterile assembly of non-hazardous material and nothing else.
2. Vertical flow drops from above. Air passes down through a filter in the roof of the cabinet onto the work surface. It is friendlier to bulky apparatus, spares the operator a direct stream of anything volatile, and is the usual choice where the work surface is crowded.
3. Neither contains an aerosol. A laminar flow hood exhausts into the room. If the work generates an infectious or toxic aerosol, the correct enclosure is a biosafety cabinet, which filters the exhaust and holds an inflow barrier at the opening. This is the single decision on this page that has consequences beyond cost.
4. Filter integrity is certified, not assumed. The high efficiency filter is tested in place at installation and periodically afterwards, and the test is what tells you the seal and the medium are intact. A hood with an unknown certification date is producing clean air only in principle.

The room matters as much as the cabinet

Laminar flow is destroyed by cross draughts. Site the cabinet away from doors, corridors, air conditioning outlets and busy traffic, and check what happens when the door opens rather than when the room is still. Many disappointing contamination results are a siting problem wearing an equipment problem's clothes.

Bench loading matters too. Objects placed upstream of the work cast a wake that carries particles downstream, so the layout inside the cabinet is a working practice to be taught rather than a detail.

What to ask a supplier

Ask for the filter certification method and who performs it locally, because a cabinet whose certifier is a long way away will drift out of test. Ask what the pre-filter regime is and how filter loading is indicated, since a loaded filter reduces velocity long before anything alarms.

Ask about noise and vibration if the cabinet sits where somebody works all day, and ask about the worktop material if you intend to disinfect it aggressively, because repeated disinfection is hard on some surfaces.

Common questions

Does a laminar flow hood protect the operator?

No. It protects the work from airborne particles and exhausts into the room. For operator or environmental protection you need a biosafety cabinet or a fume hood, depending on whether the hazard is biological or chemical.

Horizontal or vertical laminar flow?

Horizontal gives the cleanest presentation to the work and blows toward the operator. Vertical is better with bulky apparatus and keeps the stream off the operator's face. Choose vertical if there is any doubt.

How often should the filter be certified?

At installation, after any move, and on a periodic schedule set by your quality system. The date and the method should be recorded on the cabinet where anybody working at it can see them.

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