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Case study · Chemical manufacturing · Fume cupboards
A manufacturer of pet shampoos and grooming products ran two fume cupboards in its formulation lab. One passed its thorough examination comfortably. The other failed - not because of a broken fan, but because of where it had been installed. This is how a fume cupboard test works, and why position matters as much as power.
The site
The business blends and bottles shampoos, conditioners and grooming products for pets. Behind the production floor sits a small formulation and quality lab where new batches are weighed, mixed and checked - and that is where the two fume cupboards live.
Formulating cosmetics, even for animals, means handling concentrated surfactants, fragrance oils, preservatives, pH adjusters and the occasional solvent. Weighed out and blended in the open, these give off vapours and fine mists that irritate the eyes and airways, and some fragrance and preservative chemicals are recognised skin and respiratory sensitisers. The two fume cupboards are the engineering control that keeps those contaminants away from the people doing the work.
Both had been installed when the lab was fitted out and both looked identical from the front. The examination set out to answer a simple question for each: does air flow into this cupboard fast enough, and evenly enough, to keep what is inside it inside it?
The hazard and the law
A chemical fume cupboard is local exhaust ventilation in the fullest sense: it captures airborne contaminant at source and takes it away from the operator. Under Regulation 9 of COSHH it must therefore be thoroughly examined and tested at least every 14 months by a competent person, with the record kept - the same duty that applies to a welding bench or a woodworking machine.
What makes a fume cupboard distinctive is that its control is judged largely on face velocity - the speed of air drawn in across the open sash. UK guidance treats roughly 0.5 m/s as the working minimum for general work with hazardous substances, measured at the defined sash opening, with higher figures for higher-risk tasks. But a single average is not enough on its own: the velocity has to be reasonably even across the whole face and stable over time. A cupboard that averages 0.5 m/s but is fast on one side and slack on the other can still let contaminant roll back out of the slow zone.
What we tested
On each cupboard we measured face velocity across a grid of points at the working sash height, so we could see not just the average but how even the flow was from side to side and top to bottom. We then ran a qualitative containment check - releasing a visible tracer at the face and watching whether it was drawn cleanly in or allowed to spill out - and inspected the sash mechanism, the airflow alarm, the ductwork and the extract fan.
Crucially, we also looked at the room. Fume cupboard performance is notoriously sensitive to draughts, and the examination has to take in what is happening around the cupboard, not just inside it. A doorway on the wrong wall, a pedestal fan, a walkway, even a person passing close to the sash can set up a cross-flow that overwhelms the inward draught the cupboard depends on.
What we found
| Unit | Average face velocity | Evenness / containment | Result |
|---|---|---|---|
| Fume cupboard 1 (weighing) | ~0.52 m/s | Even across the face; tracer drawn in cleanly | Pass |
| Fume cupboard 2 (blending) | ~0.35 m/s | Low and turbulent; tracer rolled back out at the near edge | Fail |
Cupboard 1 did exactly what it should: an even face velocity comfortably above the working minimum, and a tracer that disappeared into the back of the cupboard the moment it was released.
Cupboard 2 was the interesting one. Its extract fan was perfectly healthy, yet its face velocity measured low and its flow was turbulent, and the containment check showed tracer rolling back out at the edge nearest the door. The cause was not the cupboard but its position: it had been installed close to a doorway with a general-ventilation fan beyond it, and the resulting cross-draught was sweeping across the open face, fighting the inward flow the cupboard needed. On paper the unit was sound; in that spot, it could not contain.
The remedial actions
Because the fault was environmental rather than mechanical, the remedial actions were about the room as much as the cupboard:
The outcome
With the cross-draught managed and the face velocity re-profiled, cupboard 2 passed its re-test and now contains as it should. The lab has a dated record for both units, a marked working sash height, and a clear understanding that the door at the end of the room is not to be propped open.
The takeaway is that a fume cupboard is only as good as the air around it. Businesses often assume a cupboard that spins up and sounds powerful must be protecting the operator, and spend money replacing fans when the real culprit is a draught from a door, a window or a fan fitted later. The thorough examination is what distinguishes the two - and in this case it turned what looked like a failing cupboard into a free fix and a safer lab. If you have added ventilation, moved benches or changed a doorway near a fume cupboard since its last test, it is worth re-checking containment, whatever the fan sounds like.
Sources and further reading
The duties, exposure limits and control standards described here come from the Health and Safety Executive. For your own process, always work from the current HSE guidance:
Questions
For general work with substances hazardous to health, UK guidance treats around 0.5 m/s average face velocity as the working minimum; a cupboard reading below that should not be relied on. Higher-risk work can call for more. Just as important is that the velocity is reasonably even across the whole face and stable, not fast in one corner and slack in another.
We measure the face velocity across a grid of points at the defined sash opening, check the velocity is even and within range, carry out a smoke or qualitative containment check to confirm contaminated air is drawn in rather than spilling out, and inspect the sash, airflow alarm, ductwork and fan. The method follows HSG258 and the principles of BS EN 14175, and the result is recorded point by point.
Because capture at a fume cupboard depends on undisturbed airflow into the face, and a cross-draught can wreck it. The failed cupboard sat where a doorway and a nearby fan created a cross-flow across its opening, so air that should have been drawn in was being pushed back out - the face velocity was both low and turbulent. The extract fan was fine; the installation position was the problem.
Often, yes. Fume cupboards and other capture hoods are surprisingly sensitive to draughts from doors, windows, walkways, pedestal fans and even people walking past. Removing the source of the cross-draught, relocating the cupboard, or screening it can restore proper containment without touching the fan at all. The examination identifies which it is.
Formulation typically handles surfactants, fragrances, preservatives, pH adjusters and colourants. Several of these can irritate the eyes, skin and airways, and some fragrance and preservative chemicals are sensitisers. A fume cupboard is the engineering control that keeps vapours, mists and dusts out of the formulator's breathing zone while they weigh and blend.
At least every 14 months under COSHH Regulation 9, the same interval as any other LEV. Because a cupboard's performance can be knocked off by something as simple as a new fan installed nearby or a propped-open door, it is also worth re-checking after any change to the room around it.
Tell us your capture points and the process they control, and we will quote the thorough examination and test to COSHH and HSG258.
