Diisocyanates & Isocyanates

Understanding Hazards and Safety Measures

Welcome to the Commodious Knowledge Bank guide on isocyanates and diisocyanates.

What are Isocyanates?

Isocyanates are a group of low molecular weight organic compounds that are widely used in the production of polyurethanes, polyurethane foam, coatings, adhesives, and elastomers. These chemicals are a leading cause of occupational exposure to respiratory hazards and respiratory disease, including severe asthma, in the UK workplace.

Isocyanates are commonly found in industries such as the motor vehicle repair and automobile industry, construction, and manufacturing. While essential for products like truck bed liners, spray polyurethane foam, and rigid or flexible polyurethane materials, exposure to isocyanates can cause chronic health effects, inflammation, and irritation of the respiratory tracts and mucous membranes of the eyes.

This guide explains what isocyanates are, the difference between types of isocyanates, the health hazards they pose, and how employers and workers can apply best practices and safety measures to control risk.

Whether you are a tradesperson, supervisor, or business owner, this article will help you:

• Understand what isocyanates are and where they are used

• Recognise the health risks and early warning signs of exposure

• Apply effective control measures in your workplace environment

• Comply with legal duties under the COSHH Regulations

• Identify appropriate training and health hazard evaluations

Scroll to the bottom of this page for our complete collection of in-depth isocyanate guides.

Isocyanates: What They Are, and Where They're Found

Isocyanates are a family of reactive chemical compounds that contain one or more isocyanate groups (-NCO). These powerful irritants react with other chemicals to create polyurethane products such as foams, coatings, adhesives, and sealants.

Common workplace products containing isocyanates include:

• Two-pack (2K) polyurethane paints are used in motor vehicle repair and refinishing

• Spray polyurethane foam insulation and coatings are used in construction

• Polyurethane glues, sealants, and floor coatings

• Rigid and flexible plastics, foam furniture, and elastomers

When sprayed, heated, or mixed, isocyanates release invisible vapours or fine mists that can be inhaled. Because they are often odourless, workers may not realise they are exposed to these respiratory hazards. Exposure can occur in both the workplace environment and during the production of polyurethanes.

Isocyanates and Diisocyanates: What’s the Difference?

Understanding the difference between isocyanates and diisocyanates helps identify which products carry the greatest risk of occupational exposure.

• Isocyanates are chemical compounds containing one or more reactive -NCO groups, used in coatings, adhesives, and foams.

• Diisocyanates are a subgroup of isocyanates containing two -NCO groups per molecule, making them highly reactive. These are often used in polyurethane production, spray polyurethane foam, truck bed liners, and high-performance coatings.

Common diisocyanates in the workplace include:

• TDI (Toluene diisocyanate) – used in flexible foam and coatings

• MDI (Methylene bisphenyl diisocyanate) – used in rigid foams and adhesives

• HDI (Hexamethylene diisocyanate) – common in spray paints and automotive coatings

• IPDI (Isophorone diisocyanate) – used in high-performance coatings and sealants

• Naphthalene diisocyanate (NDI) – used in elastomers

• Phenyl isocyanate and aryl isocyanates – used in specialised polyurethane applications

Most occupational exposure occurs from diisocyanate-based products, particularly in the automobile industry, motor vehicle repair, and during spray polyurethane foam application. All forms can cause respiratory disease, severe asthma, skin sensitisation, and inflammation of the mucous membranes of the eyes.

Health Risks of Isocyanates Exposure

Exposure can occur through inhalation or skin contact, causing both short- and long-term chronic health effects.

Short-term symptoms may include:

• Irritation of the eyes, nose, throat, and mucous membranes

• Coughing, wheezing, or breathlessness

• Skin redness, itching, or rash

Long-term health effects:

• Occupational asthma – often permanent; even small exposures can trigger respiratory disease after sensitisation

• Dermatitis from repeated contact with isocyanate-containing products

• Inflammation of the respiratory tracts and chronic respiratory disease

Workers who notice symptoms should report them immediately and seek medical advice. Case reports from the International Isocyanate Institute (ISI) highlight the importance of early intervention to prevent permanent damage.

What Should You Do if You Think You Have Been Exposed to Isocyanates?

Immediate action is essential to prevent severe asthma or other long-term health problems:

1. Leave the area and move to fresh air immediately.

2. Remove contaminated clothing carefully to avoid spreading chemicals.

3. Wash exposed skin thoroughly with soap and water.

4. Seek medical advice promptly, even if symptoms appear mild.

5. Inform your employer or supervisor to record and investigate the incident under COSHH.

6. Do not return to work involving isocyanates until medically cleared.

Early symptoms to watch for:

• Cough, wheezing, or chest tightness

• Shortness of breath

• Eye or skin irritation

• Red, itchy, or blistered skin

Employers should review control measures, respiratory protective equipment (RPE), and health surveillance following any suspected exposure.

Common Work Situations Involving Isocyanates Examples

Certain industries and tasks carry a higher risk of occupational exposure:

• Motor vehicle repair and automobile industry: Spray painting, cleaning, or maintenance using 2K polyurethane paints

• Construction: Applying spray polyurethane foam, coatings, adhesives, or sealants

• Manufacturing and production of polyurethanes: Foam, elastomers, plastics, and furniture

• Maintenance and cleaning: Handling equipment previously exposed to isocyanates

Spraying and mixing create airborne mists and vapours that can spread throughout the workplace environment.

Read more about the Safe Use of Isocyanates, training requirements and options.

Controlling Exposure: How to Work Safely

COSHH requires employers to prevent or control exposure to hazardous substances.

Hierarchy of control:

1. Eliminate or substitute – use non-isocyanate alternatives if possible.

2. Engineering controls – use enclosed spray booths, ventilation, and LEV.

3. Work practices – close spray booths, allow clearance time, never spray outside controlled areas.

4. Personal protective equipment (PPE) – air-fed respirators, chemical-resistant gloves, overalls, and eye protection.

5. Training and supervision – ensure workers understand best practices and proper PPE use.

Download our free COSHH Risk Assessment Template to help you conduct reduce risks and remain compliant.

Find out about Control Measures for Isocyanates in our article where we break down the details of isocyanates control measures.

Monitoring and Health Surveillance

Employers must ensure that controls are working through air monitoring and biological monitoring. This includes urine testing for metabolites.

Health surveillance includes:

• Lung function (spirometry) testing

• Respiratory questionnaires

• Skin checks

These measures help identify early signs of respiratory disease or severe asthma. Find out more information about Monitoring and Health Surveillance in our dedicated article.

Employer Legal Responsibilities

Under COSHH 2002, employers must:

• Conduct a suitable and sufficient risk assessment

• Prevent or control exposure using hierarchy of control

• Provide information, instruction, and training

• Monitor occupational exposure and carry out health surveillance

• Maintain safety data sheets (SDS) and exposure records

• Review controls and update them when work changes

Failure to comply may result in enforcement action by the HSE.

To understand all the Isocyanates Legal Responsibilities for Employers read our Knowledge Bank article.

Isocyanates Training and Awareness

COSHH training provides the foundation to understand:

• Health hazards, chronic health effects, and respiratory disease risks

• Best practices for handling hazardous substances like isocyanates

• Use of respiratory protective equipment (RPE) and PPE

• Conducting health hazard evaluations

Commodious offers accredited COSHH Awareness Training to help employers meet their legal obligations and reduce the risk of exposure.

Conclusion – Protecting Health Through Awareness and Control

Isocyanates are a serious workplace hazard, but risks can be prevented.

By following best practices, using proper RPE, maintaining safety data sheets, and implementing health surveillance, workers can stay safe in the production of polyurethanes, the automobile industry, or any other workplace environment where isocyanates are present.

Take immediate action if exposure occurs, report any symptoms, and ensure your team receives appropriate COSHH training.