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 :


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:

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:

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:

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:

Inspector action required on clearance times

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:

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

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:

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

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:

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:

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:

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