Reducing ill health from isocyanate exposure in motor vehicle repair (MVR)

SIM 03/2012/01


This guidance is about reducing ill health in the MVR industry by controlling isocyanate exposure.

It updates and consolidates information previously contained in SIM 03/2006/4 'Reducing ill health in the motor vehicle repair (MVR) industry' and SIM 03/2008/11 'Controlling isocyanate exposure in MVR – the role of biological monitoring'.

It also revises enforcement advice on spray space clearance times and exposure monitoring by urine samples contained in the Topic Inspection Pack Control of isocyanate exposure in motor vehicle repair (mvr) bodyshops (Version 7 10/07).


Exposure to isocyanates contained in vehicle spray paints has been the biggest cause of occupational asthma in the UK for more than a decade. Key sources of exposure are described in Appendix 1.

Although suitable air-fed respiratory protective equipment (RPE) has been widely used in the industry for many years, the number of cases of occupational asthma has remained fairly constant.

Industry norms have been agreed and established for measuring and marking spray space clearance times and for exposure monitoring using urine samples. More needs to be done to ensure that :

  • clearance times are understood and correctly employed
  • suitable RPE is being supplied, used and maintained;
  • sprayer behaviour doesn't result in inadvertent exposure;
  • biological monitoring of sprayers is carried out (to help identify where higher exposures are occurring before the onset of symptoms and asthma).


Inspectors should ensure effective control of exposure to isocyanates when they inspect vehicle paint spraying activities, including checking that clearance times have been measured, displayed and are observed (see Appendix 2).

Inspectors should consult the standards outlined in the Topic Inspection Pack (TIP) Control of isocyanate exposure in motor vehicle repair bodyshops.

The MVR bodyshop national project described in parts 1-5 of the TIP is no longer running. However, the range of issues and controls outlined in part 1 are still relevant, as modified by the updated actions and references in the Appendices to this guidance addressing:

  • Clearance times
  • Minimum standards for spray rooms
  • Exposure monitoring
  • Types of RPE to use
  • Supplied breathing air quantity and quality
  • Health surveillance

It is important to observe sprayer behaviour as well as seeing that engineering control is maintained properly, etc.


Isocyanate is the biggest single cause of occupational asthma (OA) in the UK and 'vehicle paint sprayers' are the work group at greatest risk. It is estimated that this group is 80 times more likely to suffer occupational asthma than the average UK worker. Allowing for under-reporting it is estimated that upwards of 50 cases of OA occur each year to vehicle paint sprayers. Most sufferers will stop working in MVR. This is despite the fact that air-fed RPE has been increasingly supplied to, and used by, MVR paint sprayers.

'Two pack' paints are used in virtually every MVR bodyshop. There is currently no other product that gives such a hard wearing, and high quality finish. The 'hardener' element of most two pack paint contains isocyanates, including many 'water-based' two pack paints. There is currently no isocyanate-free topcoat (ie lacquer). Whilst some non-isocyanate primers are available, top coats and lacquers are likely to contain isocyanates for the foreseeable future.

The paint industry continues to research substitute materials and have been suggested. However, any paint having similar properties is likely to be highly reactive and have similar adverse health effects on humans.


OPSTD Manufacturing Sector, Metals, Minerals and Engineering Industries Team.

Further references

Guidance not already linked or referred to above include:

Appendix 1: Health effects and exposure

Key sources of exposure

The key sources of isocyanate exposure in an MVR bodyshop have been identified as:

  • Paint spraying is overwhelmingly the most important source. Task-based exposures in spray booths will be in the hundreds of micrograms per cubic metre of air (µg/m3) and in spray rooms exposure will be an order of magnitude higher; in the thousands of µg/m3. Both are well in excess of the long and short-term limit values of 20 µg/m3 and 70 µg/m3.
  • Visor raising. The sprayer has only approx 15 seconds to restart spraying before the paint starts to set and it has become custom and practice  to raise their air-fed visor for an unrestricted view to check the quality of the finish almost immediately after finishing spraying. This behaviour was taught in initial training and has not changed over time. However, HSL have found that sprayers almost never need to start respraying making this practice unnecessary. As the spray mist contains high concentrations of isocyanate it is vital that sprayers keep their RPE on until the booth/room is clear (or they have left it), so this behaviour should be strongly discouraged.
  • Poorly controlled spray gun cleaning is the other potential major source. If the gun is cleaned with thinners and sprayed through (whether in a booth or, inappropriately, outside in the workshop) exposure in the hundreds of µg/m3 can occur.

Inspector action required on activities leading to exposure

Raise awareness of the health risks and key sources of exposure outlined above and the myths below.


Various erroneous beliefs have developed in the industry and need to be dispelled so that people can concentrate on the important causes of exposure.

Evidence from visits to well over a hundred bodyshops shows that MVR bodyshop workers believe the main health effect caused by isocyanates is cancer. There is no clear evidence to support this and it detracts from the real problem, which is that isocyanates are the single biggest cause of occupational asthma.

Many sprayers believe that a significant – or even the main – route of entry for isocyanate paint spray is through the skin, with the "thin skin around the eyes" being a particular concern. This is incorrect.

Although drips/splashes (generally during mixing of the paint) on the hands/skin can cause dermatitis, the overwhelming route of entry in MVR bodyshops is through inhalation of fine airborne paint mist. That is what puts sprayers at risk of getting occupational asthma.

Activities not of concern

Activities and tasks previously thought to cause significant exposure have now been shown not to be a problem. These include:

  • Paint mixing - good natural ventilation is adequate to dilute any solvent vapour and the very small amount of isocyanate vapour that might be released when the hardener tin is opened.
  • Dry sanding fresh 2-pack isocyanate paint film - there is no isocyanate detectable in the dust. But the fine dust generated by this process (and largely invisible under normal lighting conditions) should be controlled using on-tool exhaust extraction.
  • Paint baking (in spray-bake booths) - was thought to generate significant isocyanate monomer levels in the recirculating air. Measurements by HSL show that the levels involved are insignificant. Even so, it would be prudent and good practice to allow a purge time, when all air in the booth was discharged to atmosphere through a stack (as occurs during painting) to allow the booth to clear of paint 'fume' and any products of combustion from the baking heater.
  • Brush and roller painting - tests by HSL show that rollering and brushing body panels produces no measurable airborne exposure to isocyanates but gloves are required to protect against drips and splashes on the skin (to protect against dermatitis).

Appendix 2: Mist generation and clearance

Paint mist

Even modern spray guns (that comply with environmental legislation) waste nearly 40% of the paint used and most of this "over-spray" is propelled into the air by the jet-action of the spray gun.

Spray painters do not see most of the airborne paint mist they are exposed to. Paint spraying creates large clouds of fine paint mist, which like sanding dust, is invisible under normal lighting conditions. This can be breathed in when, for instance, the sprayer lifts their visor to view the quality of the paintwork or takes off his air-fed breathing apparatus before the booth/room has cleared. Priming the spray gun and cleaning the gun by spraying through thinners will also create an isocyanate-containing mist.

There are a series of videos on the HSE website showing how exposure occurs in paint spraying.

The majority of sprayers (and their employers) do not appreciate that fine paint mist remains in the booth/room for some time after they have finished spraying.

The fine, invisible, airborne mist needs to be removed by the extraction system. Under normal lighting, the over-spray appears to be extracted more-or-less instantaneously. In fact, the fine mist spreads throughout the spray area and circulates in vortices against the walls, and other parts, of the booth.

Clearance time

The time taken to dilute and remove the mist after spraying ceases is known as the 'clearance time' and varies enormously depending on booth or spray room design and characteristics.

Clearance time is important because spray rooms are much less effective devices than spray booths. Exposure within rooms is much higher and clearance times are much longer.

The way that air re-circulates within a booth or room will depend on air input and extract arrangements and dimensions. Fully-extracted floors can clear in less than 30 seconds, downdraught spray-bake booths with pit extraction might take up to 5 minutes and spray rooms (typically having a wall fan and filtered inlets) can take over 20 minutes.

To be confident that the booth/room is clear, whoever has to use or enter a spray booth or room must know the clearance time and when the most recent spraying was finished.

Measuring clearance time

HSL has developed automatic timing devices using both pressure and flow switches that indicate when the clearance time has passed and it is safe to enter the spray booth/space or remove air-fed breathing apparatus. However, these are not generally used within the industry at present and would currently be considered beyond what is sufficient to achieve compliance in typical bodyshop circumstances.

Fine paint mist behaves like smoke in air. A fog-generator can be used to find out how long fine paint mist takes to clear from a booth or spray room. Professional machines are typically used in theatres and clubs (and typically cost over £500), but cheaper versions retail for between £40 and £200.

Professional smoke generators are available in each Division for Inspectors to use.

To measure clearance time:

  • Set up the booth for a normal spray job (though it may be preferable to carryout the test without a car in-situ as glycerine-derived smoke can leave an oily deposit);
  • Carry out the test just before the booths filters are due to be replaced because this is when the extraction efficiency is likely to be at its lowest;
  • Switch off the extraction and fill the room with smoke from the fog generator (you should not be able to see the opposite wall viewed from the longest side). With some fog machines this may take several minutes;
  • Switch the extraction on and measure the time taken to clear the area of smoke;
  • To make the smoke more visible a parallel-beam light source (eg a 1 to 3 million candle power rechargeable spot lamp, particularly those that can be mounted on a tripod) can usefully be employed. At the same time, someone standing outside should check the booth/spray space for leaks from joints, ductwork, door seals etc.
  • Repeat the process a sufficient number of times to establish a reliable benchmark (ie at least twice if the clearance time is approximately the same, more if the times differ significantly).
  • Note the clearance time, rounded up to the nearest quarter minute, and display clearly outside the spray booth/room.

Inspector action required on clearance times

  • Ensure that clearance times have been measured (following the method outlined above or an equivalent) and notices prominently displayed on or adjacent to entrance doors to spray booths and rooms.
  • This is no longer a new requirement and is almost universally accepted in the MVR industry. It has been agreed, by HSE and the industry, to be an 'appropriate organisational measure' necessary to meet the requirement of The Control of Substances Hazardous to Health 2002 (COSHH) Reg 7(3)(b) (though there may be other ways to comply with the law). The Enforcement Management Model (EMM) indicates that an Improvement Notice may be appropriate where it has not been done.

Appendix 3: Spray rooms versus spray booths

A spray room is a dedicated room with a fan or fans in a wall. Entry of replacement air maybe planned or unplanned.

A spray booth is a purpose built unit. In a typical downdraught booth, filtered air is blown through the ceiling and sucked out through filters in the floor, although other input/output arrangements exist.

The typical clearance time for a spray booth is up to 5 minutes, whereas it can be more than 20 minutes for a spray room.

Inspector action required on spray room standards

Despite their inefficiency, spray rooms can continue to be used provided:

  • They do not leak
  • The extracted air is effectively filtered and discharged safely (eg above roof level)
  • Suitable precautions are taken after spraying until it is cleared (eg the sprayed object must not be removed and air-fed RPE must be used by anyone in the room)
  • Arrangements are made so that the sprayer can leave and enter the room safely during the clearance time. One way is to put the compressed air supply plug-in point outside the room and include a draught-strip, or similar, so that the air-supply hose can be pulled into the room and out when the sprayer leaves. Anyone entering or leaving a spray room (with a long clearance time) would need to adopt a similar procedure.

Appendix 4: RPE

Types of RPE to be used for spraying

Filtering respirators are not suitable for spraying isocyanate paints. The RPE must be air-fed breathing apparatus (BA). For preference the device should be a visor type air-fed BA, (certified to BS EN 14594:2005). It should be Class 4 and should include a low-flow indicator (which may be visual or audible).

As described in Appendix 1, many sprayers lift their visor to check the work they have just completed, not realising they are still surrounded by paint mist. As explained in Appendix 1, this practice is not necessary and must stop if they are to be properly protected.

Visibility through the face piece visor can be assisted by using tear-off visor covers (which cost less than £1 each) and by ensuring that light covers are kept clean and lamps replaced when necessary.

If vision is inadequate then half-mask BA (with constant airflow supply) conforming to BS EN 14594: 2005 may be suitable. A separate visor, to protect against paint splashes, may be required when using half-mask BA.

However, it is not clear that half-mask air-fed BA will provide adequate protection in a spray room at the high levels of isocyanate exposure encountered during spraying (isocyanate levels can rise into the thousands of micrograms per cubic metre of air). So the use of half-mask BA in spray rooms should be allowed only if there is a clear demonstration of risk control through effective and ongoing biological monitoring.

Quantity and Quality of supplied breathing air

If an insufficient quantity of air is supplied to the BA it may not provide adequate protection to the user. The British Standard for visor-type devices does not specify air volume flow rate, but each manufacturer should specify "minimum flow conditions" in terms of tubing length and internal bore and air pressure - see manufacturer's manual for details.

The standards for half-mask air-fed devices specify a minimum airflow rate of 120 l/min and, if adjustable, a maximum airflow rate of at least 300 l/min. The low-flow warning device should be designed so that it immediately draws the attention of the wearer to the fact that the apparatus is not supplying the manufacturer's minimum design flow rate.

The COSHH Approved Code of Practice suggests that air supplied to a breathing apparatus should be tested at least every three months to ensure that it meets the standards laid out in BSEN 529:2005 "Guide to implementing an effective respiratory protective device programme". It may be possible to extend the period of inspection to 6 months or, at most, yearly if there is sufficient supporting information to provide confidence in air quality (eg previous air quality test results, location of compressor, weekly maintenance log to show cleaning of traps, logging of filter checks and replacements).

Inspector action required on RPE and breathing air supply

  • Ensure suitable RPE is provided and used
  • Strongly discourage the practice of visor raising, explaining the risks of doing it, the potential lack of need to do it and practical alternatives (eg using cheap tear-off visor covers and by ensuring that light covers are kept clean)  
  • Allow the use of half-mask BA in spray rooms only with a clear demonstration of effective and ongoing biological monitoring
  • Ensure the breathing air supply is being correctly tested at suitable intervals

Appendix 5(a): Measuring isocyanate exposure

Exposure monitoring

In HSE's view the risk assessment required under COSHH for spraying of isocyanate paints in MVR should identify that exposure monitoring is requisite under COSHH Regulation 10 (1). This view is supported by paragraph 193(a) of the COSHH ACOP because:

  • employees spraying isocyanates in MVR are within an atmosphere of high airborne concentration, much higher than the WEL;
  • the sprayer's only protection is by use of air fed breathing apparatus (BA);
  • working practices have commonly been found to include removing the air-fed BA immediately after spraying to observe the quality of the paint finish and/or to exit the booth before the clearance time has elapsed;
  • 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 BA.

Checking exposure to isocyanate is particularly important where spraying is carried out in a spray room, as isocyanate levels can rise into the thousands of micrograms per cubic metre of air

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.

HSL refined this method of biological monitoring some years ago and it has been used extensively in MVR bodyshops for some years. It is a validated technique to determine whether spay painters, wearing air-fed BA, are being adequately protected and sets a benchmark against which to compare exposure measurement results.

The HSE Working Group for the Assessment of Toxic Chemicals (WATCH) committee has set 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.

Several insurance companies now require their MVR client companies to undertake urine testing to show that exposure to isocyanates is being controlled and there is good evidence to show that standards of control are improving as a result.

Urine testing in practice

Since SIM 03/2006/04 was published, the number of samples conducted nationally has risen from an average of 200 per year to over 5500 in 2010.

The frequency of urine samples for spray-painters should typically be once per year (but would be more frequent if half-mask BA is used in spray rooms) and currently costs about £50 per sample.

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. Consequently, care should be taken to ensure that 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 health service 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 that exposure has been controlled by the corrective action, these samples are usually reported as being 'clear'.

There are a number of laboratories undertaking such work in the UK.

Inspector action required on measuring isocyanate exposure

  • Ensure that all spray-painters are being suitably monitored for isocyanate exposure at appropriate intervals (at least once per year, or more frequently for painters using half-mask BA in spray rooms).
  • Monitoring for isocyanate exposure in MVR using urine testing is now an industry established method for demonstrating that control is being achieved. Inspectors should now consider issuing an IN where urine testing is not being carried out. See Appendix 5(b) for advice on wording Notices
  • Ensure that, where monitoring has indicated isocyanate exposure, the source has been identified, appropriate corrective action promptly taken and exposure retested to confirm it has been effective.

Appendix 5(b): Advice on Enforcement Notices for measuring isocyanate exposure

The EMM indicates that an Improvement Notice (IN) would be appropriate unless the employer can demonstrate by some other method that adequate control is being achieved. To the Sector's knowledge no employer has argued that they have demonstrated adequate control by any other method

Three basic scenarios have been considered:

  • 1. An Inspector identifies that a suitable and sufficient COSHH assessment has been undertaken and it has identified that exposure monitoring (ie biological monitoring – urine sampling post shift) is necessary. This is probably most likely where a third party consultant has undertaken the assessment. However, the dutyholder has not subsequently implemented any monitoring in practice.
    • This is a direct contravention of Regulation 10(1) of COSHH. An Inspector could consider issuing an Improvement Notice specifying Regulation 10(1) as the sole contravention and using the wording directly from this regulation as the reasons for the Inspector's opinion and stating that the urine sampling has not been undertaken. The information in this guidance provides background information as a basis of the Inspector's opinion.
    • Inspectors may consider that there is no need to issue a Schedule, as the measures needed to comply with the notice are obvious (ie provide a urine testing programme). Inspectors should, however, consider referring to relevant guidance (listed below) in the accompanying letter which is sent to the dutyholder.
  • 2. An Inspector identifies that the COSHH assessment is not suitable and sufficient purely on the basis that exposure monitoring (ie urine sampling) has not been identified or even considered as being necessary.
    • Because of the way in which Regulation 10 is written (ie it refers back to the assessment in Reg 6), FOD Legal have advised that any IN must be formulated around Regulation 6 only (assessment) and this is listed as the sole contravention
    • A suggested form of words for the Inspector's opinion is:
      • "You as an employer are carrying out work which is liable to expose your employees to a substance hazardous to health, namely isocyanates in paint mist, and you have not made a suitable and sufficient assessment of the risk created by that work to the health of those employees and of the steps that need to be taken to meet the requirements of Control of Substances Hazardous to Health Regulations 2002 as amended because you have not identified that urine sampling as being necessary and have not considered the results of such sampling."
    • Similarly, a Schedule may not be necessary in this instance as the steps to comply with the IN are obvious. It may be necessary to give a reasonable time for compliance to enable sampling to be arranged and results to be considered.
  • 3. An Inspector identifies that the COSHH assessment has not been carried out, or is not suitable and sufficient on a number of issues which includes the issue of the lack of identification and consideration of biological monitoring as being necessary.  The contravention is of Regulation 6 only.
    • A suggested form of words for the Inspector's opinion is:
      • "You as an employer are carrying out work which is liable to expose your employees to a substance hazardous to health, namely isocyanates in paint mist, and you have not made a suitable and sufficient assessment of the risk created by that work to the health of those employees and of the steps that need to be taken to meet the requirements of Control of Substances Hazardous to Health Regulations 2002 as amended because………."
    • Inspectors may wish to leave their reasons in general terms which may depend on what deficiencies were found making the assessment not suitable and sufficient. However, the Schedule must be specific in what issues are deficient or missing and what is required of the dutyholder.
    • The following suggested form of words for the Schedule is based upon the list of matters referred to in Regulation 6(2). Any of the matters (a) to (l) which are satisfactory within the assessment seen (or conveyed if no record is necessary) should be deleted from the list, as appropriate:
    • "To comply with this Notice you should:
      • A. Ensure that a suitable and sufficient assessment of the health risks to employees from exposure to isocyanates in paint mist, being a substance hazardous to health, is completed. The assessment for exposure to isocyanates should consider/include the following [delete as appropriate];
        • the hazardous properties of the substance;
        • information on the health effects provided by the supplier including information contained in any safety data sheet (or other reliable sources);
        • the level, type and duration of exposure;
        • the circumstances of the work, including the amount of the substance involved;
        • activities such as maintenance, where there may be the potential for a high level of exposure;
        • the relevant workplace exposure limit for inhalation for isocyanates in air is 0.02mg.m-3 (8 hour time weighted average) and 0.07mg.m-3 (short term limit);
        • the effect of preventive or control measures provided in accordance with Regulation 7;
        • the results of any relevant health surveillance (if relevant eg lung function testing);
        • the results of any monitoring of exposure in accordance with Regulation 10 [biological monitoring is deemed as exposure monitoring for isocyanates, the biological monitoring guidance value (BMGV) is 1 μmol urinary diamine/mol creatinine in urine];
        • where work involves exposure to other substances hazardous to health, the risk presented by exposure to such substances in combination;
        • and any additional relevant information you may need in order to complete this assessment;


      • B. Make arrangements as necessary to ensure that this assessment is reviewed, for example, when changes are made to the process where there is reason to believe that the assessment is no longer valid or there has been a significant change in the work to which the assessment relates.


      • C. Take any other equally effective action to remedy the said contravention."

The Inspector may wish to give more detailed guidance in any accompanying letter on biological monitoring (for all three options above). This may include reference to:

Appendix 5(c): Advice on Appeals against Notices

In the event of an appeal against an IN the Sector and/or the SG Occupational Hygienist should be able to provide evidence on:

  • The prevalence of occupational asthma amongst MVR isocyanate paint sprayers
  • The consultation with industry representatives that took place during the development of the SIM
  • The programme of MVR SHADS (2005-2007) and numbers attending etc where the need for biological monitoring was explained
  • The numbers of biological samples received by HSL and SAL from MVR isocyanate paint sprayers

Further information on biological monitoring can be found in the HSE publication Biological Monitoring in the Workplace (HSG 167)

Appendix 6: Health surveillance

Respiratory disease

Bodyshops should already have arranged for occupational health surveillance for the respiratory effects of isocyanates – see INDG 388(rev1) for details.


Workers in body preparation are twice as likely as the average working population to develop debilitating skin disease. This is probably caused by a combination of:

  • exposure to fine dust during hand sanding that cause abrasion and drying of the skin ('mechanical' damage); and
  • exposure to skin sensitisers found in two-part adhesives, body fillers and foam fillers.

Epoxy resins, especially those based on bisphenol A-epichlorhydrin, are among the most common causes of occupational allergic contact dermatitis and are used extensively in bodyshops. As a minimum, a 'responsible person' (who could be a suitably trained employee) should carry out monthly skin inspections of body preparation workers and sprayers.

Isocyanates are also classified as skin sensitisers. Under normal spraying conditions the amount of skin contact and therefore level of risk of sensitisation is very low.

Nevertheless, ill-health statistics show that spray painters are seven times more likely to develop dermatitis than the average working population. This is probably due to direct contact with liquid paint drips and spills, solvents during mixing, gun cleaning and the use of aggressive skin cleaners.

Inspector action required on health surveillance

  • Ensure occupational health surveillance has been arranged for the respiratory effects of isocyanates
  • Ensure employees have been informed of the risks they face, the symptoms to look out for and the simple control measures they can take. Control measures for dermatitis include:
    • Using nitrile gloves (rather than latex) for paint mixing, spraying and gun-cleaning;
    • Preventing contamination by not re-using disposable gloves;
    • Silk glove liners can be used to keep the hands dry. Liners can be washed at the end of the day and left to dry overnight in a clean area;
    • Implementing a skin care program is particularly important for cases where gloves may be inappropriate (eg wet sanding of body fillers may require bare hands to check the smoothness of finish)
  • Ensure any skin problems identified by the responsible person have been recorded and referred to a medical specialist.

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