Isocyanate Exposure: Symptoms, Health Effects and Prevention

Isocyanate exposure happens when workers breathe in isocyanate vapour, spray mist or dust, or get these chemicals on their skin, and it is one of the best-known workplace causes of occupational asthma. Isocyanates are used in two-pack paints, lacquers, polyurethane foams, adhesives, varnishes and plastics, so spray painters, panel beaters, powder coaters, foam and plastics workers and paint manufacturers are among those most at risk. Isocyanate exposure can irritate the eyes, skin and airways, and repeated or high exposures can lead to sensitisation, where even very small future exposures may trigger asthma. This guide explains where isocyanates are found, the symptoms to look out for, possible long-term health effects and how employers can reduce the risk.

What are isocyanates and where are they found?

Isocyanates are a group of highly reactive chemicals used to make polyurethane products. Safe Work Australia’s Guide to handling isocyanates lists the most widely used industrial isocyanates and their main uses, including:

• Toluene diisocyanate (TDI): flexible polyurethane foam production
• Methylene diphenyl diisocyanate (MDI): rigid polyurethane foam production
• Hexamethylene diisocyanate (HDI): spray paints, lacquers and car refinishing
• Naphthalene diisocyanate (NDI): elastomers and synthetic rubbers
• Isophorone diisocyanate (IPDI): coating and adhesive polymers and polyurethane foams

In everyday work terms, isocyanates are found in two-pack (2K) paints and clear coats, paint hardeners, polyurethane foams and insulation, adhesives, timber floor varnishes, synthetic rubbers and some plastics. A paint hardener labelled as containing “no free isocyanates” may still be hazardous, because it can contain a high proportion of polymeric isocyanates that have similar health effects when sprayed.

Isocyanates can also be generated at work. Heating or burning polyurethane, such as hot wire-cutting foam, welding through polyurethane-lagged pipe or heating coated metal, can break the material down and release isocyanates into the air.

Workers with the highest potential for exposure include those in vehicle repair and refinishing, where panel beaters and spray painters regularly use two-pack coatings, as well as furniture and cabinet makers, spa manufacturers, powder coating operations, foam and plastics manufacturing, and paint and coatings manufacturers. If you work across the wider painting trade, our article on occupational exposures in the painting industry covers isocyanates alongside other common hazards.

How isocyanate exposure happens at work

According to Safe Work Australia, isocyanate exposure most commonly occurs by breathing in vapours, mists, aerosols or dusts. Isocyanates and their breakdown products can also be absorbed through the skin or eyes. The main ways workers are exposed include:

• Spraying: spray painting creates a fine mist that is easily inhaled. Even partially polymerised (pre-polymer) isocyanates carry the same health risks as free isocyanates once sprayed.
• Mixing and heating: heating isocyanates, or the heat produced during chemical reactions such as foaming, increases the amount of vapour released.
• Sanding and grinding: sanding polyurethane paint that has not fully cured can create dust containing unreacted isocyanates.
• Skin contact: splashes, contaminated gloves or clothing, and handling uncured products.
• Thermal breakdown: welding, cutting or burning polyurethane materials.

Because spray mist can be very fine, workers may not see or smell anything unusual while they are being exposed. That is one reason isocyanate exposure needs to be managed through controls and monitoring rather than relying on the senses.

Isocyanate poisoning symptoms: what to look out for

People often search for “isocyanate poisoning symptoms”, but in the workplace the more common picture is irritation and allergic-type reactions of the airways, skin and eyes. Symptoms can vary from person to person and depend on the type of isocyanate, how much a worker is exposed to and for how long.

Breathing and airway symptoms

Safe Work Australia lists the following possible symptoms of inhaling isocyanates:

• irritation of the nose, mouth, throat and lungs
• difficulty breathing
• chest tightness, coughing, wheezing and shortness of breath
• other asthma-like symptoms
• headache and general discomfort

SafeWork NSW also notes that inhalation can cause nausea, vomiting and headaches.

Skin and eye symptoms

Isocyanates are skin and eye irritants. Contact can cause redness, swelling, blistering and skin irritation, and longer-term skin exposure can lead to dermatitis. Splashes to the eyes can cause chemical conjunctivitis.

Delayed symptoms

Respiratory symptoms do not always appear straight away. Safe Work Australia notes they may be delayed, appearing at night or several hours after working with isocyanates. Workers may not connect a cough or wheeze in the evening with spraying earlier in the day, so it is important they know about delayed symptoms and report them. Any worker who develops wheezing, coughing or difficulty breathing that may be related to isocyanate exposure should be assessed by a medical practitioner.

Sensitisation and occupational asthma

The most important health concern with isocyanates is sensitisation. Many isocyanates are respiratory sensitisers, and some are skin sensitisers. Once a worker becomes sensitised, exposure to airborne levels well below the workplace exposure standard can cause asthma-type reactions such as chest tightness, wheezing, shortness of breath and narrowing of the airways. Safe Work Australia warns that this can be life threatening if exposure continues.

Key points about sensitisation from Safe Work Australia’s guidance:

• Sensitisation usually develops some time after first exposure. The time is highly variable, from several weeks to two years or more, and in around 20 per cent of cases it can be 10 years or more.
• A single high exposure, such as from a spill, may lead to sensitisation.
• Lower-level exposure over a long period may also lead to sensitisation or a decline in lung function.
• Skin exposure is thought to contribute to respiratory problems, so skin protection matters as well as breathing protection.
• There is currently no screening test to identify which individuals are susceptible to respiratory sensitisation.
• A worker diagnosed as sensitised should be removed from potential exposure.

Because there is no way to predict who will become sensitised, preventing exposure in the first place, and picking up early changes through health monitoring, is the most effective approach.

Isocyanate poisoning long-term effects

The long-term effects of isocyanate exposure relate mainly to the lungs and skin. Possible long-term effects described by Australian regulators include:

• Occupational asthma: once sensitised, a worker may continue to react to very low levels of isocyanates.
• Reduced lung function: lower-level exposure over time may contribute to a decline in lung function.
• Chronic skin conditions: including irritant and allergic dermatitis, hives and rashes.
• Other chronic effects: SafeWork NSW states that chronic exposure may cause liver and kidney disease, chronic lung damage and cancer.

On cancer, Safe Work Australia notes that some isocyanates, including forms of MDI and TDI, are classifiable under the Globally Harmonized System (GHS) as Carcinogenicity Category 2, meaning they are suspected of causing cancer. Exposure to suspected carcinogens should be eliminated or minimised so far as is reasonably practicable.

How long do isocyanates stay in the body?

Once absorbed, isocyanates are broken down and their breakdown products (metabolites) are passed out in urine. The UK Health and Safety Executive (HSE) explains that, because of the rate at which these metabolites are excreted, a urine sample taken at the end of a shift only shows exposure for that shift.

The health effects, however, can last much longer than the chemical. Once a worker is sensitised, that sensitivity can persist, and later exposures may trigger symptoms even at very low levels. So while the question “how long do isocyanates stay in the body” has a fairly short answer for the chemical, the more important issue for workers and employers is preventing sensitisation and lasting airway changes.

Isocyanate exposure testing and health monitoring

Isocyanate exposure testing at work generally falls into three areas:

• Air monitoring: measures airborne isocyanate levels against the workplace exposure standard (0.02 mg/m³ as an 8-hour time-weighted average and 0.07 mg/m³ as a 15-minute short-term limit). It is required where it is uncertain whether the exposure standard is being exceeded.
• Biological monitoring: strategically timed urine testing can show whether a worker has recently been exposed and helps check whether controls are working.
• Health monitoring: isocyanates are listed in Schedule 14 of the WHS Regulations, so health monitoring is required where there is a significant risk to health from exposure. It focuses on respiratory health, and records must be kept for 30 years.

Health monitoring helps identify early changes in breathing or skin health so that a doctor can advise on the worker’s health and the employer can review exposure controls. For details of what an assessment involves and how often workers are monitored, see our guide to isocyanate health monitoring. For an overview of your legal obligations across all Schedule 14 hazardous chemicals, read our article on health monitoring requirements.

Reducing isocyanate exposure in the workplace

Under WHS laws, businesses must eliminate or minimise risks so far as is reasonably practicable, working through the hierarchy of controls. Safe Work Australia’s guidance gives examples for isocyanates:

• Substitution: using an isocyanate-free single-pack paint instead of a two-pack product where suitable, brushing instead of spraying, or using high volume, low pressure (HVLP) spray guns that create less fine mist.
• Isolation and engineering controls: enclosing or automating processes, using spray booths built and maintained to AS/NZS 4114, and fitting local exhaust ventilation with suitable filtration.
• Administrative controls: restricting access to spraying areas, limiting time near isocyanates, keeping other workers away and providing training on hazards, symptoms and how to report them.
• Personal protective equipment: supplied-air (positive pressure) respirators where enclosure and ventilation are not enough, full-face rather than half-face respirators, and chemical-resistant gloves (nitrile rather than thin latex), overalls and eye protection.

Safe Work Australia notes that organic vapour respirators with particulate pre-filters and powered air-purifying respirators are not suitable when spraying isocyanates, as they do not provide adequate protection. Contaminated clothing should be removed immediately and decontaminated before it is worn again, and control measures must be reviewed if health monitoring results indicate a review is needed.

How Employees Health can help with isocyanate exposure

Employees Health is a doctor-led occupational health provider that has supported Australian workplaces for 30 years, since 1996, under the clinical leadership of Chief Medical Officer Dr Mike Shenouda. We provide health surveillance anywhere in Australia, either onsite at your metro, regional or remote workplace, or at a clinic, so your team can be assessed with minimal disruption to production.

Our isocyanate health surveillance medicals are designed for workers in spray painting, vehicle refinishing, powder coating, foam, plastics and paint manufacturing. The program is doctor-led, and employers receive clear, properly documented reports to support their WHS obligations and record-keeping.

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Talk to our team about isocyanate health monitoring for your workforce, wherever you are in Australia. Call 1300 880 804, email our team or send us an enquiry.

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