By workplace & process
The invisible mist from two-pack paint is the leading cause of occupational asthma. A booth controls it - and the booth is LEV that has to be tested.
The short answer
Spraying two-pack, or 2K, paint creates a fine, invisible mist containing isocyanates - the most common cause of occupational asthma in the UK, and a cause of dermatitis. The spray booth is not just a clean space to paint in; it is the local exhaust ventilation that controls that mist, and as LEV it falls squarely under COSHH. Testing it is testing the control the sprayer's lungs depend on.
The detail
Isocyanate mist is invisible under normal lighting and spreads through the air like smoke, so a sprayer can be over-exposed without seeing anything. Motor vehicle repair paint sprayers have long been substantially more likely to develop occupational asthma than any other occupation, and once someone is sensitised, even a tiny future exposure can trigger a serious attack that may end their career. The HSE takes this seriously enough to run large targeted inspection campaigns of body shops using isocyanate paints.
Control rests on several things working together. Spraying must be done inside a properly performing booth or room, never outside it. The sprayer must wear air-fed breathing apparatus while mist is present and must not lift the visor too soon. The booth should run at slight negative pressure, so that any leak draws air inward rather than letting mist escape. And exposure is verified by biological monitoring - a urine sample analysed for a marker of isocyanate uptake, with a guidance value that triggers investigation if exceeded.
What it means for you
The single most important operational number is the clearance time - how long the booth takes to clear of fine mist after spraying stops. It is measured with a smoke or fog generator, marked clearly on the booth door, and everyone who uses the booth must know it, because entering or lifting a visor before the booth has cleared is where exposure happens. A thorough examination and test checks that the booth extraction achieves and holds the airflow it was commissioned to, that filters and ducts are sound, and that the clearance time is still valid, at least every fourteen months.
The typical failing is a booth whose extraction has weakened, lengthening the real clearance time beyond the figure on the door - so operators re-enter into mist that has not actually gone. Testing catches that drift before it becomes exposure.
The service behind the guide
We test spray booths and rooms as LEV, including verifying clearance time, and give you a dated report with any remedial actions the booth needs.
Questions
Yes. A spray booth or room is the local exhaust ventilation that controls paint mist, so it falls under COSHH and must be thoroughly examined and tested like any other LEV system.
It contains isocyanates, the most common cause of occupational asthma in the UK. The mist is invisible under normal lighting, and once a sprayer is sensitised even a tiny exposure can trigger a serious attack.
The time a booth takes to clear of fine paint mist after spraying stops. It is measured with a smoke generator, marked on the booth door, and must be known by everyone using the booth, because entering too soon is where exposure occurs.
So that any leak draws air into the booth rather than letting isocyanate mist escape into the workshop where other people are working.
Through biological monitoring - a urine sample analysed for a marker of isocyanate uptake. A guidance value is set, and exceeding it should trigger an investigation into the workplace controls.
Phoenix Duct Clean · by the numbers
We examine body shop spray booths and rooms against the control they must provide, including clearance time, and report clearly. Call or email to book.