LEV and Spray Booths: Isocyanate Control for Vehicle Paint and Body Shops

Isocyanates are the biggest cause of occupational asthma in the UK. In the motor vehicle repair trade, the source is two-pack (2K) paints and lacquers — the products that give a car a hard, durable, high-gloss finish. Spraying them releases an isocyanate mist that, breathed in, can cause asthma that lasts a lifetime.

Occupational asthma from isocyanates is permanent. Once a worker becomes sensitised, even tiny exposures can trigger a severe attack. There is no safe level of exposure for a sensitised person. The only reliable protection is to control the mist at the point it is created and to keep it out of the air everyone else breathes.

That is what a spray booth — a form of local exhaust ventilation — is for.

Why Isocyanates Are So Dangerous

Two-pack paints contain isocyanate hardeners. When you spray them, you create a fine mist of paint droplets carrying isocyanate. Breathing that mist exposes the lungs directly. The HSE's motor vehicle repair guidance identifies 2K paint spraying as the highest-risk task in a body shop.

The danger is not limited to the sprayer. Isocyanate mist that escapes the booth can drift across the workshop and sensitise other workers who never pick up a spray gun. This is why control is about the whole workshop, not just the person holding the trigger.

Isocyanates can also cause dermatitis and irritation of the eyes, nose and throat. But the headline risk — and the reason the HSE runs targeted inspection campaigns in this sector — is occupational asthma.

The Workplace Exposure Limit for Isocyanates

The workplace exposure limit for isocyanates is set in EH40:

• Isocyanates (all, as –NCO): 0.02 mg/m³ (8-hour time-weighted average)
• Short-term exposure limit: 0.07 mg/m³ (15-minute reference period)

Isocyanates are also flagged as a respiratory sensitiser. As with all sensitisers, COSHH Regulation 7 requires exposure to be reduced so far as is reasonably practicable, not merely kept below the limit. For a substance this hazardous, the duty is to design the exposure out wherever you can.

The Spray Booth as a COSHH LEV System

A spray booth or spray room is a local exhaust ventilation system. It draws air across the work, captures the paint mist, and removes it through extract filters and ductwork. Like any LEV used to control a hazardous substance, it is governed by COSHH and must be:

• Suitable — designed and sized to capture the mist generated by the spraying it is used for
• Used correctly — operating before spraying starts and for the full clearance time afterwards
• Maintained — filters changed on schedule, fans and seals kept in good order
• Thoroughly examined and tested — at least once every 14 months under COSHH Regulation 9

A booth should keep the spraying area under slight negative pressure relative to the rest of the workshop, so mist is drawn into the extraction rather than leaking out into shared space.

Clearance Time: The Number Every Body Shop Must Know

After spraying stops, the booth keeps running to clear the mist from the air. The time this takes is the clearance time, and the HSE's guidance is specific about it:

• A spray booth typically clears in less than 5 minutes
• A spray room can take 20 minutes or longer
• You must know the clearance time for your specific booth or room
• It should be measured with a smoke generator, and the test done under worst-case conditions, such as just before the extract filters are due for replacement
• The clearance time should be displayed at the entrance to the booth, so everyone knows how long to wait before entering without air-fed protection

No one should enter the booth, or remove their air-fed breathing apparatus, until the clearance time has passed. Getting this wrong is one of the most common ways body shop workers are exposed unnecessarily.

Respiratory Protection for Spraying

Even a well-functioning booth does not protect the sprayer standing inside it, in the mist. For 2K spraying, the HSE is clear that filtering respirators are not adequate. Sprayers must use air-fed respiratory protective equipment — constant-flow air-fed breathing apparatus, typically a visor or hood type, with an assigned protection factor of at least 40 and a low-flow indicator.

The air supply must be clean and of breathing quality. The RPE must be maintained, and the wearer must be trained to use it and to keep it on until the clearance time has passed.

TExT and Records for Spray Booths

Because a spray booth is LEV controlling a hazardous substance, it falls squarely within COSHH Regulation 9: thorough examination and test at least every 14 months, with records kept for at least five years.

The TExT for a spray booth checks that extraction rates, air movement and filtration are still adequate to control the mist — not just that the fan turns on. Between formal tests, you should carry out and record regular user checks, and act on any defect that affects performance.

Our guide on how often LEV must be tested explains the 14-month rule, and the LEV testing due date calculator works out the next deadline for each booth or extraction system you operate.

HSE Enforcement in Motor Vehicle Repair

Motor vehicle repair is a long-standing HSE inspection priority, driven by the high rate of occupational asthma in the trade. Inspectors visiting body shops will look closely at how isocyanate exposure is controlled.

During an inspection, the HSE will typically check:

• Whether a risk assessment identifies 2K spraying and the controls needed
• Whether spraying is done in a properly functioning booth or room
• Whether the clearance time is known, displayed, and observed
• Whether sprayers use air-fed RPE that is suitable and maintained
• Whether the booth has a current TExT report within the 14-month window
• Whether records of testing, maintenance, filter changes and user checks are available
• Whether health surveillance is in place for those who spray

Practical Compliance Steps

1. Confine spraying to the booth. All 2K spraying should happen inside the spray booth or room, never in the open workshop.

2. Measure and display your clearance time. Use a smoke test under worst-case conditions, display the result at the booth entrance, and make sure everyone waits it out.

3. Use air-fed RPE for spraying. Constant-flow air-fed breathing apparatus, APF at least 40, with a clean breathing-quality air supply.

4. Bring the booth into the TExT regime. Thorough examination and test within 14 months, every cycle. Use the LEV compliance checklist generator to assess your extraction.

5. Maintain filters and extraction. Change extract filters on schedule. Falling extraction or rising clearance time is a warning that the booth is losing performance.

6. Keep your records. TExT reports, filter-change logs, user checks. The record-keeping requirements checker confirms you are meeting the requirements.

7. Arrange health surveillance. Workers who spray 2K paints should be under health surveillance to catch early signs of sensitisation.

LEVproof is being built to help UK body shops and workshops manage LEV compliance — booth TExT tracking, automated reminders, and digital record-keeping. Join the waitlist for early access.

Sources

• Control of Substances Hazardous to Health Regulations 2002 (COSHH) — legislation.gov.uk
• EH40/2005 Workplace exposure limits — HSE
• 2-pack isocyanate paints — motor vehicle repair — HSE
• Motor vehicle repair (MVR) — HSE
• HSG258: Controlling airborne contaminants at work — HSE

This guide summarises published HSE and government guidance. It does not constitute legal advice. Consult a qualified professional for advice specific to your situation.