Paint sprayer with suspected isocyanate asthma: diagnosis, fitness and exposure control
A 34-year-old paint sprayer at a vehicle refinishing workshop has had 18 months of wheeze, chest tightness and nocturnal cough. Symptoms began about 6 months after he started using two-pack isocyanate paints and improve at weekends and on a two-week holiday; he has a 10 pack-year smoking history. FEV1 is 88% predicted, FEV1/FVC 0.74, FeNO 48 ppb, and methacholine PC20 is 1.2 mg/mL. He works in a spray booth with local exhaust ventilation, but the booth has had no LEV examination for 3 years. His employer wants him to stay on the same job and asks you to 'sign him off'. There is no occupational health nurse on site.
1. How would you interpret the clinical findings, and what further investigation would you arrange before advising the employer?
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Interpretation
- The temporal pattern is the key: symptoms began after a latent interval of about 6 months from first isocyanate exposure, improve away from work, and he has nocturnal symptoms. This fits sensitisation to a workplace asthmagen rather than simple irritation.
- Objective support: elevated FeNO (48 ppb) and a positive methacholine challenge (PC20 1.2 mg/mL) confirm variable airway hyperresponsiveness. FEV1/FVC 0.74 is not clearly obstructive, but asthma can be present with normal spirometry between exposures.
- Smoking is a confounder but does not explain work-related improvement; it should be addressed separately.
Further investigation
- Serial peak expiratory flow: 2-hourly from waking to sleeping for at least 3–4 weeks, including work weeks and at least one week away from work, plotted and scored (e.g. Oasys). This is the most useful confirmatory test when done well.
- Specific IgE to isocyanate–albumin conjugates: useful if positive because specificity is high, but sensitivity is limited, so a negative result does not exclude occupational asthma.
- Refer to a specialist occupational lung disease centre for specific inhalation challenge if the diagnosis remains uncertain and the job decision is difficult.
- Review the workplace: LEV examination records, booth capture velocity, respiratory protective equipment fit testing, skin contact, and whether two-pack paints are used outside the booth.
- Do not certify him fit for unrestricted isocyanate work while the diagnosis is unresolved.
2. What advice would you give the employer about his continued exposure, and how would you handle the request to certify him fit for the same job?
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- Advise temporary removal from isocyanate exposure until investigation is complete. Reducing exposure is not a reliable safe option: sensitised workers can react to very low concentrations, and continued exposure worsens prognosis.
- Suggest redeployment to a non-isocyanate task (e.g. preparation, masking, non-two-pack work) with the same terms and conditions where possible, and review at 4–6 weeks.
- If occupational asthma is confirmed, advise permanent avoidance of isocyanates and discuss the implications: RIDDOR reporting of occupational asthma, possible Industrial Injuries Disablement Benefit, and the need to inform his GP and respiratory specialist.
- Explain to the employer that you cannot 'sign him off' as fit for the same job while he has work-related symptoms and an unresolved diagnosis. Certification should be explicit about restrictions and review dates, not a blanket fit note.
- Obtain his consent before sharing clinical details; provide the minimum necessary information to the employer.
3. What action would you recommend for the LEV system and the wider workforce?
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- The absence of LEV examination for 3 years is a breach of COSHH duties; LEV must be thoroughly examined and tested at least every 14 months, and more often for some processes. Advise immediate examination by a competent person and repair if deficient.
- Review the COSHH assessment for two-pack isocyanates: enclosure, extraction, RPE with fit testing, skin protection, training, spill procedures and emergency arrangements.
- Introduce health surveillance for isocyanate-exposed workers: baseline and annual respiratory questionnaire and spirometry, with prompt referral for anyone reporting work-related respiratory symptoms.
- Consider whether other workers have similar symptoms; a workplace walk-through and questionnaire may reveal further cases.
- Record your advice in writing and set a review date; if the employer does not act, explain the regulatory position and consider escalation through the normal HSE route.