Construction hazardous substances: Isocyanates

You can find isocyanates in a number of construction products including polyurethane paints, coatings, foams, glues and flooring. Certain tasks, such as spraying, can produce very high exposure to isocyanates. This page tells you how to control these risks and why.

What you must do

The Control of Substances Hazardous to Health (COSHH) Regulations says you must protect against the risks from isocyanates. Follow the Assess, Control and Review model. Pay particular attention to:


Identify and assess: Identify tasks where you will be using products containing isocyanates. Consider:

  • Who – think about your employees. Who is using products containing isocyanates? Is anyone else likely to be around who might be affected by the work you are doing? This includes members of the public.
  • What – which product are you using? You can find isocyanates in a number of products including polyurethane paints, coatings, foams, glues and flooring. Isocyanates also come in different forms – eg TDI is more hazardous because it is more volatile. Look at the packaging and safety data sheet. Are there any other substances hazardous to health in the product such as solvents.
  • How – think about how you will be doing the work. The more spray / mist that is made the greater the risk. Spraying (link to sub page below) tasks can produce very high exposure to isocyanates.
  • Where – the more enclosed the space, the greater the risk may be. This depends on what you are doing and how you are doing it.

Use this information to identify the level of risk. Workers are generally at lower risk of inhaling isocyanates if they are applying the products with hand tools like brushes or trowels. In contrast, spraying is a higher risk task. Seek specialist help if you are unsure.


Where the risks are judged to be low, simple and inexpensive controls will suffice.  For other tasks, like spraying, you will have to do more. The range of isocyanate containing products and the tasks you can use these for mean that you must decide on the specific controls you need based upon your assessment of the risks. Take specialist help if you unsure about this. Give priority to the greatest risks first.

Prevent: Where possible think about eliminating or reducing isocyanate risks. Consider:

  • using products that do not contain isocyanates or less volatile forms
  • avoiding unnecessary spraying. This causes more isocyanate to get into the air compared to using a brush or roller
  • being aware of anyone who is already sensitised to isocyanates. Keep them away from the work

Control: Even if you minimise some of the risk this way, you may still need to control isocyanate risks. Control this by using the appropriate measures below:

  • Ventilation – make sure there is enough fresh air in the work area. Open doors and windows etc. The higher the risk the better the ventilation will need to be;  
  • Eye protection – wear eye protection (eg goggles or a face shield) when doing work where splashes / aerosol may get into the eyes.
  • Glovesgloves should be right for the products you are using – single use disposable gloves made of suitable materials (eg nitrile) are preferable. Make sure the breakthrough time and permeation rate are right for the type and length of the work. Check with the manufacturer / supplier. You may need gauntlet style gloves to prevent skin exposure.
  • Overalls – disposable overalls are preferred. Launder significantly contaminated re-usable overalls before wearing them again.
  • Washing – good washing facilities are essential. Wash off any product on the skin as soon as possible. Do not use solvents to do this. Workers should be encouraged to wash exposed skin at breaks and after finishing work. Skin care products can also help replace the natural oils that help keep the skin's protective barrier working properly.
  • Respiratory Protective Equipment (RPE) – you may need RPE where ventilation does not provide enough control – particularly in enclosed spaces if you are creating an aerosol (eg by some rollering work) or using products with significant amounts of TDI. Wearers should be fit tested where needed. It is particularly important to select the correct filter. For example, P3 particulate filters provide protection against spray mist but do not protect you from vapours. You will need the right gas / vapour filter for these. Change them at suitable intervals. Check with your supplier if you're not sure.
  • First aid – give adequate and appropriate first aid treatment to anyone affected by isocyanates. You may also need to seek further medical attention.

Train: Workers need to know how to use the controls properly. They also need to be aware of the signs and symptoms of ill-health from isocyanate exposure.


Supervise: Ensure that controls such as work methods, PPE and welfare are effective and used by the workers.

Monitor: You may need to do health surveillance if there is a reasonable likelihood of getting dermatitis from your work. It could be done by a 'responsible person'. This can be an employee with suitable training. They should:

  • assess the condition of a new worker's skin before, or as soon as possible after, they start work and then periodically check for early signs of skin disease after this
  • keep secure health records of these checks
  • tell the employer the outcome of these checks and any action needed

A competent person should perform annual lung function testing and a questionnaire for asthma if your work involves generating aerosols containing isocyanates.

What you should know

There are a number of different isocyanates. The most common are:

  • MDI – this is usually a dark brown viscous liquid but may also be found in pure form as a white to pale yellow solid (flakes). MDI has does not readily evaporate at room temperature. Higher vapour concentrations can be produced when it is heated to temperatures above 40oC.
  • TDI – this is generally a colourless to pale yellow liquid. It is one of the most volatile isocyanates with relatively high vapour pressure – ie it evaporates quickly.

Other types of isocyanates include HDI and IPDI.

Isocyanates can affect your health in a number of ways. They can cause:

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Updated 2023-04-25