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An introduction to Isocyanates - Providing an Overview

Updated: May 1, 2020

Occupational exposure to isocyanates can cause serious occupational diseases which lead to long-lasting, life-changing health problems. In these series of articles, we are going to explain the fundamentals of isocyanates, providing added information on how personal exposures can be monitored, along with further discussions around how occupational exposure can occur, explaining the health effects relating to the substances.

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What Are Isocyanates?

Isocyanates are a group of organic chemical compounds which are produced from amines by phosgeniation. Isocyanates are used predominantly in the production of polyurethanes and polymers.

Isocyanates are highly reactive agents. These types of substances are electrophiles, highly reactive with nucleophiles. Which makes isocyanate exposures difficult to measure as the substance reacts with the moisture in the air.

Isocyanates can be reacted with water to generate Carbon Dioxide in the formation of polyurethane foams. Carbon Dioxide functions as a blowing agent, expanding the polyurethane into a foam-like material which sets.

An organic compound with two isocyanate groups is classed as a Diisocyanate.

Methylene diphenyl diisocyanate (MDI), most often abbreviated as MDI, is an aromatic diisocyanate. Hexamethylene diisocyanate (HDI) is the organic compound with the formula (CH₂)₆(NCO)₂. Toluene diisocyanate (TDI) is an organic compound with the formula CH₃C₆H₃(NCO)₂.

How Are Isocyanates Used?

The Centre For Disease Control and Prevention states that Isocyanates are used in many processes, particularly ones which undertake the manufacturing or use of flexible and rigid foams, fibres, coatings (such as paints and varnishes) and elastomers. They are increasingly used in the automobile industry, in autobody repair, and in building insulation materials.

Isocyanates react with compounds containing alcohols to produce polyurethane polymers - which are used in polyurethane foams, thermoplastic elastomers and “2 pack” type polyurethane paints to improve the performance, durability and finish of painted surfaces.

How Exposures Occur

In many processes, Isocyanate based products are applied by spraying, which poses a risk to health through inhalation and also skin contact. Spray-on polyurethane products containing isocyanates have been developed for a wide range of retail, commercial, and industrial uses to protect cement, wood, fibreglass, steel and aluminium, including protective coatings for truck beds, trailers, boats, foundations, and decks.

When sprayed, the isocyanate vapours and particulates become airborne. These are then inhaled. Inhalation of isocyanate vapour and particulate can cause severe adverse health effects, particularly occupational asthma through respiratory sensitisation.

The isocyanate can be used during polyurethane production and can be further present during the heated extrusion of polyurethane products made from thermal plastic. Isocyanates can be present in the plastic fumes along with volatile organic compounds.

An Introduction to the Health Effects

The isocyanate based substance or material (if not fully cured) can come into contact with the skin. There is evidence that humans can become sensitised to isocyanates by skin contact, causing allergic contact dermatitis.

It should be mentioned that Isocyanates are powerful irritants to the mucous membranes of the eyes and gastrointestinal and respiratory tracts. There are further reports that direct skin contact can cause marked inflammation and it is important to understand that there is evidence that both respiratory and dermal exposures can lead to sensitisation.

Sensitisation can lead to severe asthma attacks or painful skin reactions if the person is exposed again. This can occur even if they are exposed to low concentrations.

Death from severe asthma in some sensitised subjects has been reported according to NIOSH and the Centre For Disease Control and Prevention.

Exposure Symptoms

Workers potentially exposed to isocyanates experience persistent or recurring eye irritation, nasal congestion, dry or sore throat, cold-like symptoms, cough, shortness of breath, wheezing, or chest tightness. These should see a physician knowledgeable in work-related health problems as soon as possible.

Do You Need Support with COSHH?

It is hoped that this article goes some way to providing a brief overview of COSHH. If you wish to know more on this subject or need support with your COSHH assessments, exposure monitoring or the testing of your LEV systems, RPE Fit Testing then please feel free to get in touch with us through social media or our website (, by email at or simply give us a call on 01709 931299.

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