Isocyanates: What are they?

Posted in Firwood Hints and Tips by Firwood Paints Limited on September 5th 2019
Isocyanates are a family of highly reactive, low molecular weight chemicals. They are widely used in the manufacture of coatings such as varnishes and paints.

You can find isocyanates in a number of products including polyurethane paints and coatings. Certain tasks, such as spraying, can produce very high exposure to isocyanates. Later, we will discuss how to control these risks and why.

Spray-on polyurethane products containing isocyanates have been developed for a wide range of uses in commercial, and industrial retail applications to protect several surfaces such as cement, wood, steel and aluminium.

Isocyanates are powerful irritants to the mucous membranes of the eyes and respiratory and gastrointestinal tracts. Direct contact with skin can also cause inflammation. Isocyanates can also sensitize workers, making them subject to severe asthma attacks if they are exposed again. There is evidence that both respiratory and dermal exposures can lead to sensitization. Death from severe asthma in some sensitized subjects has been reported. It is recommended that workers potentially exposed to isocyanates who experience persistent or recurring eye irritation, nasal congestion, dry or sore throat, cold-like symptoms, cough, shortness of breath, wheezing, or chest tightness should see a doctor.

Preventing exposure to isocyanates is a critical step in eliminating the potential hazards to health. The principle method of minimizing isocyanate exposure in the workplace would be engineering controls such as closed systems and ventilation.

Other controls, such as worker isolation and use of PPE (personal protective equipment) such as respirators and personal protective clothing to prevent dermal exposures may also be required. Early recognition of sensitization and swift and strict elimination of exposures is necessary to reduce the risk of long-term or permanent respiratory problems for sensitized workers.

Controlling the risks of isocyanates

The Control of Substances Hazardous to Health (COSHH) Regulations says you must protect against the risks from isocyanates. You should consider following the Assess, Control, and Review model, details of which are laid out on the HSE website.

You should pay particular attention to:


  • Identify tasks where the use of isocyanates will be required.
  • Think about who is using products containing isocyanates and whether anyone else is likely to be around that might be affected by the work being undertaken, including members of the public.
  • Think about which product you are using. Isocyanates come in many different formats such as TDI, which is more volatile, and thus more hazardous. TDI 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.
  • Think about how you will be undertaking the work. Naturally, the more spray, the greater the risk. Spraying tasks can produce high risks to isocyanate exposure.
  • Think about where the work is being undertaken. The more enclosed the space, the greater the risk of exposure to isocyanates.
Using this information will help to identify the risk levels. Workers are generally at a lower chance of exposure if manually applying the coating, ie using brushes rather than sprays.


Where risks are judged to be low some simple and low cost controls will suffice. For others such as spraying you will need to do more. First assess the risks, then make an informed decision on what controls would be appropriate.

Preventing exposure is another consideration.

  • Think about using products that do not contain isocyanates where possible, or less volatile versions.
  • Avoid unnecessary spraying; where possible use a brush or roller.
  • Be aware of people sensitive to isocyanates and keep them away from the work being undertaken.

You may still need to control isocyanate risks even where risk has been minimized. You can carry out this control in the following ways:


Make sure there is enough fresh air in the working environment by opening windows and doors.

Eye protection

Where splashes or aerosol may get into the eyes goggles or face shields should be worn.


Gloves will need to be made in a suitable material, ie single use gloves made of nitrile, making sure that the breakthrough time and permeation rate are right for the type and length of the work. You should check with the supplier or manufacturer. Gauntlet style gloves may be more appropriate depending on the type of work being carried out.


Disposable overalls are preferred in this type of work. Should you use re-wearable overalls they will need to be significantly laundered after use in order to avoid contamination.


Wash any product from the skin as soon as possible. Do not use solvents to clean skin. Workers should be encouraged to wash exposed skin at breaks and after finishing work. Skin care products can also be used to replace natural oils in the skin.

Respiratory Protective Equipment (RPE)

Where ventilation does not offer enough control you may need to use RPE. This is particularly the case in confined spaces if you are creating with the use of aerosols or using products with high levels of TDI. Items should be fit tested where possible and it is important to select the correct filter, changing them at suitable intervals. For example, P3 particulate filters provide protection against spray mist but do not protect you from vapours.

First Aid

Adequate and appropriate first aid treatment should be delivered to anyone affected by isocyanates. You may also need to seek further medical attention.


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


An ongoing review of these actions is required.


Ensure the appropriate controls such as PPE are being used by your workers.


Where necessary you may need to do health surveillance if there is a likelihood of getting dermatitis from your work. This can be carried out by an employee with suitable training.

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