Isocyanates – A family of chemicals

Authors: CANUTEC Emergency Response Advisors

For immediate help, call 911 and refer to the first aid section.

For technical help, call CANUTEC at 613-996-6666 and refer to the spill response section.

Isocyanates are common chemicals used in industries. They are useful for manufacturing, but they are highly toxic products. It is important to understand how they can be dangerous.

This article summarizes information about isocyanates from CANUTEC Emergency Response Advisors.

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Introduction

Isocyanates are a family of organic chemicals containing an isocyanate group (N=C=O). They are commonly used to make polymers for products like plastics, paints, adhesives, and foams.

In 1984, an explosion in Bhopal, India released 40 tonnes of isocyanates. This industrial disaster killed thousands and injured hundreds of thousands. The toxic isocyanate cloud that formed caused chronic health issues in many victims, increasing the rate of people with respiratory issues.

There are many different types of isocyanate chemicals. Three specific chemicals are most commonly used today:

  • diphenylmethane-4,-4’-diisocyanate (also known as methylene bisphenyl isocyanate, MDI):
    • the most commonly encountered isocyanate, mostly in the construction and automotive industry
    • used to make rigid or flexible polyurethane foam used in thermoplastics, sealants, coatings, and adhesives
  • toluene-2,4-diisocyanate (TDI):
    • used to make polyurethane foams
    • used for furniture, bedding, insulation, and paints
  • hexamethylene-1,6-diisocyanate (HDI):
    • used to prepare medical adsorbents, exterior paint, dental materials and contact lenses

These chemicals are all shipped commercially as a liquid.

Many UN numbers are used to classify isocyanates. Most are classified as toxic substances (class 6.1), flammable liquids (class 3), or both. The dangers of isocyanate exposure are well known in industries that commonly handle them. However, it is always important to stay up to date on information about these substances and how to handle them properly and safely.

Potential hazards

Isocyanates are highly toxic. Repeated exposure is dangerous to your health. Exposure is usually through inhalation and skin contact.

MDI, TDI and HDI do not produce much vapour, due to their low vapour pressures. However, they all have a threshold limit value – time-weighted average (TLV-TWA) of 0.005 ppm. This means that people handling isocyanates should not be exposed to more than this amount for an average 8-hour workday in a 40-hour work week.

This low exposure limit is because isocyanates are sensitizing. This means people can develop allergy-like reactions, asthma or breathing difficulties when exposed by inhalation or skin contact. Occupational asthma and skin redness is common among workers who handle isocyanates due to overexposure.

Some isocyanates are also flammable or can polymerize when heated. They may easily ignite with a source of ignition like heat, light, sparks, or flames. If they are heated in a container, the container may over-pressurize, rupture, and release hazardous vapours.

Storage

Isocyanates are usually transported as a liquid due to their relatively low melting point. Isocyanates should be stored in a cool and well-ventilated area away from heat sources and direct sunlight. This prevents the dangerous buildup of pressure inside containers.

Safe storage procedures are especially important because some isocyanates may polymerize when heated. For example, TDI may polymerize at temperatures above 177°C or if heated at 45°C for a prolonged period.

Isocyanates should be kept away from incompatible materials like water, bases, and strong oxidizers. Isocyanates violently react when mixed with water, producing polyureas and a large amount of carbon dioxide (CO2) gas. This CO2 gas can increase the pressure inside a container and cause it to rupture violently. Polyurea is not an immediate danger, but it can block holes in a ruptured container, leading to over-pressurization.

Contact with other incompatible material like bases and strong oxidizers can cause a violent reaction and generate heat. This increases the amount of isocyanate vapours inside the container. The heat of the reaction could also ignite other flammable products.

Handling

Isocyanates should always be handled outdoors or in a well-ventilated environment. Wear proper personal protective equipment when handling isocyanates. This includes:

  • full body covering, such as spray suits, rubber boots and gloves made of compatible material (like nitrile or butyl gloves)
  • Compatible respirators such as ones with organic vapour cartridges

First Aid

For moderate to serious exposures, call 911 or the Poison Control Centre in your area and seek medical treatment.

Isocyanates are considered toxic because they are sensitizing. This means people exposed to them develop an allergy-like reaction. People sensitized to isocyanates develop respiratory issues such as coughing, chest tightness and shortness of breath, even when exposed to low concentrations.

Sensitization is a permanent effect. It is important to avoid unnecessary contact with isocyanates to lower the risk of sensitization.

Common symptoms of isocyanate exposure include:

  • eye exposure: eye irritation, severe watering, light sensitivity, and conjunctivitis
  • inhalation exposure: respiratory irritation, coughing, difficulty breathing, chest tightness and asthma attacks
  • skin exposure: contact dermatitis, redness, swelling and blistering of the skin

If you are exposed to isocyanates:

Eyes:

  • immediately rinse eyes with lukewarm water for at least 15 minutes
  • remove contact lenses if worn

Skin:

  • remove contaminated clothing
  • wash affected area with soap and water

Inhalation:

  • immediately move to fresh air
  • seek medical attention if coughing or difficulty breathing continues

Ingestion:

  • rinse mouth with water
  • do not induce vomiting

Fire response

Different isocyanates have different levels of flammability. Isocyanates release harmful isocyanate vapours as well as nitrogen oxides, carbon monoxide and traces of hydrogen cyanide in a fire. Respiratory protection such as a self-contained breathing apparatus (SCBA) is required to prevent inhaling these toxic gases.

In a fire, evacuate the area immediately and contact the local fire department.

  • If the container is on fire, use dry chemical powder or CO2 extinguishers and large amounts of water
  • For large fires, use an unmanned hose to apply a water spray, a water fog, or alcohol resistant foam from a safe distance
  • Do not aim water directly into the container, as isocyanates will react and form solid polyurea
    • This can plug any holes that may have formed and cause the container to over-pressurize
  • Heat from a fire may cause isocyanates to polymerize and generate more vapours and gasses (such as CO2)
    • This can cause the container to over-pressurize
    • If you detect over-pressurization, evacuate at least 100 m for a small container and 800 m for a large container

Spill Response

For technical advice, call CANUTEC at 1-888-226-8832 (Canada and US only), 613-996-6666, or *666 (cellular only). For large spills, call 911 immediately.

Always use inert absorbing materials like sand or vermiculite to contain an isocyanate spill. Scoop the material into a container but do not seal the container to avoid the risk of over-pressurizing. Store the container outside or in a well-ventilated area before disposing of the product.

If the spill happened indoors, increase ventilation by opening doors and windows first. Always wear protective clothing like gloves and compatible respirators when handling an isocyanate spill.

There are decontamination solutions for isocyanate spills that can neutralize a spill. These should only be used by trained professionals. Please ask the manufacturer about appropriate solutions to use.

Disposal

The spilled material is waste. It should be disposed of according to local or provincial regulations.

Store the waste in an appropriate container first. The container should be unsealed with no lid. Keep the container outside or in a well-ventilated area to prevent vapours from accumulating. Do not keep it in an enclosed space.

Contact a local hazmat contractor to pick up the waste or your local hazardous waste facility to arrange a drop off.

Conclusion

Isocyanates are widespread chemicals that are valuable to industry. Despite their hazards, they are a relatively low risk to the average person, especially when handled appropriately.

This article is a reminder of the risks and dangers of these chemicals and how to handle isocyanate exposure. Check the safety data sheets (SDS) of products containing isocyanates to learn more about the hazards. This will lead to a safer environment and help protect the people who regularly handle these products.

References

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