Isocyanates-Deserve Your High Attention

What are isocyanates?

Isocyanates are hazardous chemicals. They are widely used in common daily spraying operations, for example, spraying of two-pack lacquers and paints containing isocyanates is common in auto refinishing and the manufacture of wood products. These coatings are supplied in two parts that are mixed together. The hardener component (usually part B) contains isocyanates, which can also be called polymeric isocyanate or isocyanate prepolymer.

Products containing isocyanates must be labelled in accordance with the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). If you see the pictograms listed below, or the signal word “DANGER” in the label, it deserves your attention. That means this product contains isocyanates.

Health Risks to Your Workers

Workers who work with, or may work with isocyanates, must be warned about the risks of exposure and the potential health effects. Spraybooth Man will list some symptoms that may happen while your workers exposed to isocyanates. While these symptoms happened in your workers, you need to stop the exposure to isocyanates and contact a medical practitioner immediately.

Inhalation effects

Symptoms of inhaling isocyanates may include:

  • irritation of the respiratory tract including the nose, mouth, throat and lungs—most isocyanates have a strong irritating effect on the respiratory tract

  • difficulty in breathing

  • tightness of the chest, coughing, wheezing and shortness of breath

  • other asthma-like symptoms, and

  • headache and discomfort.

  • If a worker develops respiratory symptoms consistent with isocyanate exposure, particularly wheezing, coughing or difficulty breathing, a medical practitioner should assess the relationship between symptoms and exposures. Depending on the severity, the worker may not be allowed further exposure to any amount of isocyanate.

Skin and eye effects

Isocyanates are skin and eye irritants.

  • Skin and eye contact with isocyanates can lead to blistering, swelling, reddening and skin irritation.

  • Exposure of the skin to isocyanates over a longer period can lead to chronic skin conditions like dermatitis.

  • Splashes to the eyes can cause chemical conjunctivitis.


People who develop sensitisation to isocyanates usually do so some time following their first exposure. This time period is highly variable. It can be several weeks or up to two years or more. In around 20 percent of cases, it can be 10 years or more.

Once sensitised, a person’s subsequent exposure to airborne concentrations well below the exposure standard can cause asthmatic reactions like chest tightness, wheezing, shortness of breath and airway narrowing. This can be life threatening if exposure continues.

Exposing sensitised workers to isocyanates may reduce their respiratory capacity immediately on exposure, some hours later or both.

Exposure to higher concentrations from spills may increase the risk of sensitisation, and even a single high exposure event may lead to sensitisation.

Lower level chronic exposures may lead to sensitisation or a decline in lung function.


Exposure to carcinogens should be eliminated or minimised to as low as reasonably practicable. The following isocyanates are classifiable according to the GHS as Carcinogenicity Category 2— suspected of causing cancer:

  • 4,4’-methylene diphenyl diisocyanate.

  • 2,2’-methylene diphenyl diisocyanate.

  • o-(p-isocyanatobenzyl) phenyl isocyanate.

  • Toluene-2,4-diisocyanate.

  • Toluene-2,6-diisocyanate.

The Other Risks

With the exception of methyl isocyanate which has a low flash point of -7° C, most isocyanates have relatively high flash points and generally present a low fire hazard. However, there are situations where the fire hazard will happen when:

  • isocyanates are present in a mixture with flammable solvents

  • the exothermic heat reaction during foam manufacture is not properly controlled, and

  • isocyanates are stored at elevated temperatures to prevent solidifying.

  • You need to take proper steps to minimise the risk of fire or explosion. If the fire happens, you need to have an effective emergency response plan, so you minimise your loss. Here are the details you need to contain in your plan and make sure that these details are up to date.

  • Names and contact details of workers who are appointed first aid officers at the workplace.

  • Contact details of emergency services including the location of the nearest medical facilities.

  • Location of evacuation points where workers can go in an emergency.

  • Emergency response actions to be taken if isocyanates are inadvertently released affecting the workplace, neighbouring businesses or residents.

  • Procedures for inspecting and maintaining emergency equipment like fire extinguishers and maintaining the contents of first aid kits.

Where your workers will be exposed to isocyanates?

As mentioned above, the exposure to isocyanates have the greatest risk to your workers and the environment. There are some situations that isocyanates may be exposed, Spray booth man reminds you to have full attention.

  • It can occur when aerosols, mists or powder paints containing isocyanates are released into the atmosphere during spraying or powder coating.

  • It can occur during sanding of polyurethane paint that is not fully cured, as this activity can generate dust containing unreacted isocyanates. 

  • Be careful about the isocyanate-containing materials which may release isocyanates into the atmosphere when heated.

Solutions to the Risks

All the health and physical risks can be eliminated or reduced by the following solutions.

using non-isocyanate-containing paints

  • using spray techniques that minimise overspray

  • using a fully enclosed spray booth that vents safely outside, ensuring that:

  • air velocities for down-draught and side-draught booths are 0.25m/s and 0.5m/s respectively

  • the booth is run for at least five minutes after spraying to allow spray mist to clear

  • the spray booth is regularly checked, tested and maintained (eg replacing filters) to ensure it is operating properly

  • using a full-face airline respirator when spraying isocyanates, ensuring that the respirator is disconnected and removed outside the booth

  • maintaining respirator air quality by:

  • checking that the compressor air intake

  • is located away from sources of contamination such as motor vehicle exhaust fumes

  • replacing consumable filters, such as particulate, coalescing and charcoal filters, in accordance with manufacturer’s recommendations.

  • keeping records of compressor and filter system servicing/maintenance

  • carrying out colour matching under local exhaust ventilation (LEV)

  • cleaning spray guns using an automated gun wash system or under LEV

  • wearing suitable gloves

  • if skin contact with ‘gun wash’ solvent is likely

  • placing lids on open containers of thinners and solvent soaked rags to prevent unnecessary exposure to solvent vapours

  • eliminating ignition sources where flammable solvents are used or stored

  • storing paints and thinners properly (ie flammable liquids storage cabinets for small quantities or designated storage room with adequate ventilation, intrinsically safe lighting and bunding)

  • providing health surveillance, including lung function testing under the supervision of a doctor.


A Health and Safety Solution | Spray Painting- Safely Spraying Isocyanate Paints, June 2017, Work Safe Victoria

Code of Practice | Spray Painting and Powder Coating, March 2015, Safe Work Australia

Guidance Note | Spraying of Flammable liquids, June 2017, Work Safe Victoria

Guide to Handling Isocyanates, July 2015, Safe Work Australia

some images are from the Internet.

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