Risk assessment required under COSHH for spraying isocyanate paints in motor vehicle repair (MVR) should identify that exposure monitoring is necessary under COSHH Regulation 10 (1) because:
- workers spraying isocyanates in MVR are within an atmosphere of high airborne concentration, much higher than the workplace exposure limit
- the sprayer's only protection is by use of air-fed breathing apparatus
- sprayers sometimes remove air-fed breathing apparatus immediately after spraying to observe the quality of the paint finish. It is important sprayers keep respiratory protective equipment (RPE) on until they have left the spraying area
- effective control relies on a combination of physical provisions which can fail or deteriorate and behaviour which can be inconsistent and inadequacies in either or both can result in a serious health effect
- high numbers of MVR paint sprayers have developed occupational asthma from isocyanate exposure despite the use of air-fed breathing apparatus
Checking exposure to isocyanate is particularly important where spraying is carried out in a spray room. This is because isocyanate levels can rise into the thousands of micrograms per cubic metre of air.
Measuring exposure to isocyanates through urine testing
The only practical way of measuring a paint sprayer's exposure to isocyanate (or anyone else using RPE) is by analysis of isocyanate metabolites in a urine sample.
This method of measurement is called biological monitoring and has been around for a number of years. It has been used extensively in MVR bodyshops. It is a suitable protocol to determine whether those liable to exposure to isocyanate aerosol, such as spray painters, are being adequately protected.
Our biological monitoring tool for dutyholders and paint sprayers can help you understand and act on your urine isocyanate test results:
The HSE document on workplace exposure limits lists a biological monitoring guidance value (BMGV) for isocyanates of 1 µmol urinary diamines/mol creatinine on the basis that a concentration of urinary diamines at or below this level is associated with adequate control of exposure.
Urine testing in practice
Thousands of urine testing samples are taken each year to ensure controls are effective in protecting workers.
The frequency of urine samples for paint sprayers should typically be once a year (but would be more frequent if half-mask breathing apparatus is used in spray rooms).
The excretion rate of the isocyanate metabolites from the body means that a urine sample taken at the end of the shift only shows exposure for that shift. Care should also be taken to ensure sampling is representative.
Urine testing for isocyanates does not provide information about a person's health, it indicates whether exposure to isocyanates is occurring. To ensure that results are interpreted correctly and appropriate remedial action is taken, suitable explanatory information should be provided by the laboratory or provider administering the scheme.
Isocyanate in the urine does not show the route of exposure. Elevated levels should initiate an investigation into how exposure is actually occurring. In most cases, control measure failures are readily identified and corrective action taken. Subsequent retesting should be arranged to ensure exposure has been controlled by the corrective action. These samples are usually reported as being 'clear'.
There are 3 laboratories carrying out such work in the UK, one of them is HSE.
Care should be taken when implementing and managing a biological monitoring programme. Support and guidance can be found in the publication Biological monitoring in the workplace: A guide to its practical application to chemical exposure.