Construction isocyanates: Spraying

Spraying can produce very high exposure to isocyanates. This page tells you how to control this risk and why. You also need to be aware of the general information on isocyanates.

What you must do

Follow the Assess, Control and Review model. Pay particular attention to:


Identify and assess: Tasks involving spraying isocyanates are particularly high risk. This is because you can easily breathe the aerosol mist droplets this produces. You also use more of the product in a shorter space of time. Anyone near this work will be at risk.


Follow the precautions for controlling general isocyanate risks for controlling isocyanate risks. In addition, you should also consider:

  • Spray equipment – choose the correct equipment for the work. Be aware of issues associated with different types of spray equipment. 'Conventional' spraying uses compressed air to atomise the paint. This can create quite a lot of overspray / mist in the air that can travel significant distances. You may improve this by using high-volume low-pressure (HVLP) spray guns. Alternatively, airless spraying forces paint through a nozzle under high pressure. There is less overspray / mist travel with this method as the speed of the paint droplets quickly falls after leaving the nozzle. However, there is risk of injecting paint etc into the skin if the spray tip is not properly guarded. Use the correct tip sizes and pressure;
  • Work area – spray in an enclosed area with local exhaust ventilation (LEV) where possible. You should ensure that:
    • spray mist does not leak out
    • extracted air is discharged to a safe place
    • suitable precautions are taken after spraying until the area has cleared, this can take a long time

It may not always be possible to do this, for example when painting some structures. Keep all non-essential people away from the work area until the risk has been minimised. Take into account wind speed and direction. This can cause spray to drift large distances.

  • Respiratory Protective Equipment (RPE) – use constant flow air-fed breathing apparatus (BA). In most instances this should have an assigned protection factor of 40 (eg a visor / hood type air-fed BA) and a low flow indicator. Make sure the breathing air is uncontaminated and meets 'minimum flow conditions' in terms of tubing length / internal bore and air pressure. Improve visibility by using tear-off visor protectors if needed.
  • Work practices – it is important to keep RPE on until you have left the spraying area / it is clear. You will be exposed to significant risk if you raise the visor of an air-fed mask to check the quality of your work etc. Cleaning the spray gun is another potential source of significant exposure if not properly controlled.


Supervise: Ensure equipment is properly used and RPE is worn correctly.

Maintain: Make sure the RPE is properly maintained. Test the air supply to ensure it is clean and safe to breathe. Check any air filters are correctly working and spray is not leaking from enclosed areas. 

Monitor: This should be done by a competent person. You are likely to need:

What you should know

Spraying isocyanate products is a significant cause of occupational asthma. Symptoms can develop immediately following exposure but can also appear several hours later outside working hours in the evening or early morning. Early signs of respiratory sensitisation to isocyanates include one or more of the following:

  • chest tightness
  • persistent cough
  • wheezing
  • breathlessness
  • flu-like shivers

If your isocyanate exposure continues, you may suffer from permanent and severe asthma. There is no cure. This can have life-changing consequences. Even a tiny amount of any isocyanate could trigger an attack. It would almost certainly mean you would have to give up this type of work.

There are a series of videos on the HSE website showing how exposure occurs in paint spraying . More general information about spraying isocyanates can be found in the motor vehicle repair section of the HSE website.

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Updated 2021-10-07