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Isocyanates - Hazards and Controls

Updated: May 23

Isocyanates are a chemical found in many products such as paints, foams, glues, and flooring. There are a number of different isocyanates such as MDI, TDI, HDI and IPDI. The most common are MDI and TDI; the former does not readily evaporate at room temperature whilst the latter is very volatile with a high vapour pressure causing it to evaporate quickly.


Isocyanates can be found across various industries, but they are particularly common in motor vehicle body shops for use in paints and lacquers as a hardener. Even if paint is considered water-based, it can still contain isocyanates. The term water-based generally means the amount of solvent is reduced, not that they are no longer toxic.

Health Effects of Isocyanates


Spraying isocyanates paints is the main cause of occupational asthma in the UK. Approximately 50 isocyanate paint sprayers are diagnosed with occupational asthma every year, resulting in most of them having to leave their industry. Once someone becomes sensitised, even an extremely low exposure can trigger an asthma attack. Typical early signs that someone is becoming sensitised to isocyanates can include one or more of the following:

  • chest tightness, often occurring outside working hours in the evening or early morning

  • persistent cough

  • recurring blocked or runny nose

  • recurring sore or watering eyes

  • wheezing

  • breathlessness

  • flu-like shivers

If an exposure continues following early symptoms, they may become permanently sensitised with occupational asthma, which has no cure. Once this has happened asthma can be triggered from other airborne pollutants or even the cold air!


What the Law Requires


The Control of Substances Hazardous to Health (COSHH) Regulations, 2002 (as amended) require employers to carry out a risk assessment for those likely exposure to isocyanates. This risk assessment should identify the controls required to ensure that exposure is either prevented or adequately controlled. Once suitable controls are in place, they must be commissioned to demonstrate that they work. The law then requires that the controls are checked and maintained, so be sure to have them examined and keep records for a minimum of 5 years.


When assessing inhalation exposure, the UK workplace exposure limit (WEL) for isocyanates is 0.02 mg.m-3 based on an 8-hour time-weighted average (TWA) whilst the short-term exposure limit (STEL) is 0.07 mg.m-3 for a 15-minute TWA. However, as isocyanates can cause occupational asthma, there is no safe level and therefore, exposure should be reduced as low as reasonably practicable (ALARP).


It is also a requirement of the COSHH Regulations to provide a suitable program of health surveillance if there is a reasonable likelihood of a disease occurring in the workplace. As isocyanates can cause Occupational Asthma and Dermatitis, the program would need to cover both skin and lung disease. The results of any health surveillance must be retained for a minimum of 40 years as required by the COSHH Regulations 2002 (as amended).


Typical Control Measures


Using isocyanate spraying as a good example of a process, we can now look at the measures you should expect to have in place:

  • Spray Equipment – Ensure the correct equipment is selected for the job. For example, spraying usually uses compressed air to atomise the paint which creates significant overspray that can travel some distance. This can be improved by selecting high-volume low-pressure spray guns.


  • Work Area – All spraying should be carried out in an enclosed area such as a room or booth. Where possible, local exhaust ventilation systems (or LEV for short) should be used. It is important that the LEV does not allow spray mist to leak out and discharge the air to a safe place. The LEV must be commissioned to demonstrate the effectiveness and then thoroughly examined and tested. We have a blog available here that provides more information on local exhaust ventilation systems and other LEV examination and testing services.


  • Respiratory Protective Equipment (RPE) – Use constant flow air-fed breathing apparatus when entering a booth or room with isocyanate spray mist present. This should have an assigned protection factor of 40 and a low flow indicator. The breathing air quality will also require testing at regular intervals to ensure it is not contaminated and meets the minimum flow requirements. We have already written blogs which you can check out by clicking here and here.


  • Occupational Exposure Monitoring - The only practical way to carry out personal exposure monitoring to isocyanates is through urine analysis of the operatives likely exposed, which should be taken at the end of the shift. The benefit of this is that it takes into account all routes of exposure and can help verify whether the RPE is being used effectively. The main drawback is that is more intrusive than other personal exposure monitoring services. Air monitoring can also be carried out where the risk assessment requires, although there are problems with the methodology which are outside the scope of this blog. To summarise, it means it is even more essential to ensure you engage incompetent help!


How we can help


At Blue Turtle Ltd, we provide a range of occupational hygiene monitoring services and can help you carry out your occupational health risk assessment. We can also help you to better understand your local exhaust ventilation systems and ensure you meet your legal obligations under the COSHH Regulations.


We help businesses of all types manage their workplace health hazards. Our experienced consultants can provide practical advice on how to achieve adequate control through process changes, improvements, or adopting/changing work practices to reduce the risk as low as reasonably practicable.


Whatever your Occupational Hygiene needs are, Blue Turtle Ltd is here to help your business protect your workforce and help you meet your legal obligations.


Give us a call today to discuss your needs or if you prefer, complete the online form with a brief outline of your business needs and/or concerns.


Blue Turtle - The missing cog in your business health!





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