What is Methyl Isocyanate?

Methyl isocyanate, also known as isocyanatomethane, methyl carbylamine, and MIC, is an organic compound with the molecular formula CH₃NCO. Under normal conditions, it is a colourless liquid with a strong, pungent smell. It evaporates quickly at room temperature and boils at 44°C. The vapours are heavy and can settle in low areas, where they might mix with air and become explosive. It’s also very flammable and reacts dangerously with water, producing urea and lots of carbon dioxide. This chemical can damage metals, plastics, rubber, and coatings. When heated, it breaks down into harmful gases like hydrogen cyanide and carbon monoxide. Methyl isocyanate is part of a group of chemicals called volatile organic compounds (VOCs), which easily turn into vapour or gas.

What is Methyl Isocyanate used for?

Methyl isocyanate is used in the chemical industry to make various important chemicals. It's also used to create synthetic rubber, adhesives, and in the production of herbicides and pesticides.

Methyl Isocyanate Hazards

Sources of exposure

Methyl isocyanate can be found in tobacco smoke, so people who smoke or breathe in second-hand smoke may be exposed to it. You can also be exposed to it by breathing it in or coming into contact with it at workplaces where it's made or used. People living near factories that produce, store, or use this chemical might breathe in small amounts of it.

Routes of Exposure

Inhalation: Breathing methyl isocyanate is the most common way people are exposed. Its vapours are easily absorbed by the lungs. The smell is only noticeable at levels much higher than what is considered safe by OSHA (0.02 ppm). Significant exposure mostly happens in workplaces.

Skin/Eye Contact: Direct contact with the liquid or strong vapours of methyl isocyanate can cause exposure. This usually only happens in work environments where the chemical is stored or used.

Ingestion: Although rare, swallowing liquid methyl isocyanate could be a way to get exposed.

Health Effects

Acute Effects

• In 1984, a gas leak of methyl isocyanate in Bhopal, India, led to over 2,000 deaths and impacted more than 170,000 survivors. Most deaths were caused by pulmonary oedema and secondary respiratory infections like bronchitis and pneumonia.
• Other effects from breathing in methyl isocyanate include irritation of the respiratory tract, trouble breathing, blindness, nausea, stomach inflammation, sweating, fever, chills, and damage to the liver and kidneys. Survivors have ongoing lung damage (such as reduced lung function and lesions) and eye problems (like vision loss and cataracts).
• Animal studies also show similar effects, including lung irritation, weight loss, and severe lung damage. 
• Acute animal tests in rats show methyl isocyanate exposure through inhalation is extremely toxic and it's also highly toxic when ingested.

Chronic Effects

• No data is available on the long-term effects of methyl isocyanate in humans or animals.
• The EPA has not set a reference concentration (RfC) or reference dose (RfD) for this chemical.
• CalEPA has set a chronic inhalation reference level of 0.001 mg/m³ based on lung and body weight effects observed in rats.

Reproductive/Developmental Effects

• Following the Bhopal incident, a high percentage of survivors experienced reproductive issues, including leukorrhea, pelvic inflammatory disease, excessive menstrual bleeding, and suppressed lactation.
• Other adverse effects included increases in the number of stillbirths, spontaneous abortions, and increased infant mortality. 
• Animal studies have reported increased incidence of fetal deaths and decreased fertility, live litter size, fetal body weight, and neonatal survival following inhalation exposure to methyl isocyanate during pregnancy.

Cancer Risk

• No information on the cancer-causing potential of methyl isocyanate in humans.
• A study with animals exposed to methyl isocyanate once via inhalation showed no significant tumour associations in mice and female rats, but a marginal increase in pancreatic tumours in male rats.
• EPA classifies methyl isocyanate as Group D, meaning it is not classifiable regarding human carcinogenicity.

Methyl Isocyanate Safety

First Aid Measures

Respiratory distress/asthma:

If someone is having trouble breathing, act quickly with the following steps, as it can become life-threatening:

• Move the person to a clean, uncontaminated area and provide oxygen.
• If they stop breathing, start artificial respiration immediately.
• If trained medical personnel are available, they may administer a bronchodilator like salbutamol using a nebuliser.
• Seek urgent medical attention.

Isocyanate splashes in the eyes:

• Rinse the eyes gently with lukewarm water for at least 15 minutes.
• If the person is wearing contact lenses, rinse for a few minutes, remove the lenses, and continue rinsing.
• Go to a doctor or hospital as soon as possible.

Isocyanate splashes on the skin:

• Remove any contaminated clothing.
• Wash the skin thoroughly with soap and water.
• Do not use solvents (e.g., methylene chloride) to clean isocyanates from the skin.
• Clothing should not be worn again until it has been fully decontaminated.

Methyl Isocyanate Safety Handling

Control Measures

To protect workers from isocyanate exposure, it’s important to minimise risks by carefully reviewing work practices. Procedures should ensure that workers are not exposed to harmful levels. Control measures include:

1. Elimination or substitution
2. Engineering controls
3. Administrative controls
4. Personal protective equipment

Engineering Controls

• Enclosure: Processes using isocyanates should be enclosed as much as possible. Ensure good ventilation to keep air concentrations below exposure limits.
• Local exhaust ventilation: If full enclosure isn’t possible, use local exhaust systems to capture vapours, especially for isocyanate or polyurethane spraying tasks involving TDI or HDI. Where aerosol formation isn’t likely, local exhaust might not be necessary if exposure remains below standards. Exhaust vapours should not be released in a way that could cause harm outside.

Personal Protective Equipment

Personal protection is necessary when exposure can’t be controlled through other methods (e.g., mixing paints or spray-painting). It’s important to remember that protective gear supplements other controls and doesn’t eliminate the hazard itself.

Key points:

• Use air-line respirators or self-contained breathing apparatus as per Australian Standard AS 1716 for tasks like paint mixing, spray painting, or cleanup.
• Organic vapour respirators with particulate filters are not suitable for isocyanates.
• Protective equipment should be chosen carefully, fitted properly, and workers trained in its use.
• Regular checks and maintenance of protective equipment are essential.
• During spills or cleanup, air-line respirators or self-contained breathing apparatus are required.
• Avoid skin and eye contact with isocyanates.
• Use resistant materials for gloves and protective clothing (e.g., Teflon, Viton, nitrile rubber, or some PVA gloves), following the guidelines in Australian Standard AS 2161.
• Contaminated clothing should be removed and not reused until properly cleaned.

Regulations

United States

• OSHA (Occupational Safety & Health Administration):
  • General Industry: Permissible Exposure Limit (PEL) for methyl isocyanate is 0.02 ppm or 0.05 mg/m³ (Skin).
• ACGIH (American Conference of Governmental Industrial Hygienists):
  • The Threshold Limit Value (TLV) for methyl isocyanate is 0.02 ppm, or 0.047 mg/m³ TWA (Skin).
• NIOSH (National Institute for Occupational Safety and Health):
  • The Recommended Exposure Limit (REL) is 0.02 ppm TWA (Skin).

Australia

• Safe Work Australia:
  • The 8-hour Time Weighted Average (TWA) exposure limit for methyl isocyanate is 0.02 mg/m2.