What is Toluene Diisocyanate?

Toluene diisocyanate (TDI) is an organic compound with the formula CH₃C₆H₃(NCO)₂. Two commercially important isomers exist:

• 2,4-TDI (CAS: 584-84-9)
• 2,6-TDI (CAS: 91-08-7)

TDI is commonly marketed as an 80/20 or 65/35 mixture of these isomers. At room temperature, it appears as a clear, colourless to pale-yellow liquid with a pungent odour. While it decomposes in water, TDI is highly soluble in acetone and benzene and can mix with solvents like ether, carbon tetrachloride, and kerosene. It is combustible and darkens when exposed to sunlight.

What is Toluene Diisocyanate used for?

TDI is mainly used in the production of flexible polyurethane foams for:

• Furniture
• Bedding
• Automotive and airline seats

Other applications include:

• Elastomers (bumpers, industrial rollers, shoe soles, mechanical parts)
• Coatings (automotive refinishing, wood finishes, anti-corrosion coatings)
• Rigid polyurethane foam (household refrigerators, insulation for vehicles and buildings)
• Adhesives & sealants (used in automobile parts, roller skate wheels, pond liners, and blood bags)
• Polyurethane-modified alkyds (floor finishes, wood coatings, paints)
• Moisture-curing coatings (wood and concrete sealants)

Some elastomer products are made from pure 2,4-TDI rather than the 80:20 mixture.

Sources & Routes of Exposure

Sources of Emission

• Industrial: Factories producing polyurethane products
• Diffuse: Emissions from polyurethane products over time
• Natural: No known natural sources
• Transport: No significant mobile sources
• Consumer Products: Found in coatings, sealers, adhesives, and polyurethane cushions (with very low emissions detected)

Routes of Exposure

Exposure to TDI can occur through:

• Inhalation
• Ingestion
• Skin contact
• Eye contact

Health Effects

Acute Effects

Short-term exposure to high levels of TDI can cause:

• Severe skin, eye, and nose irritation
• Nausea and vomiting
• Moderate to extreme toxicity from inhalation (in animal studies)

Chronic Effects

• Reduced lung function
• Asthma-like symptoms (wheezing, bronchial constriction)
• Respiratory tissue irritation
• Weight loss (observed in animal studies)

The EPA Reference Concentration (RfC) for a TDI mixture is 0.00007 mg/m³, based on respiratory effects.

Reproductive & Developmental Effects

No known reproductive or developmental effects have been reported in humans or animals.

Cancer Risk

• Human studies: No confirmed link between TDI exposure and cancer
• Animal studies: Increased tumors in the pancreas, liver, and mammary glands
• IARC Classification: Group 2B (Possible Human Carcinogen)
• EPA Classification: Not yet classified
• OSHA & NIOSH: Recommend limiting workplace exposure due to potential carcinogenic effects
• Long-term inhalation studies: Showed a dose-dependent increase in tumors in rodents
• Mechanism: Potential carcinogenicity linked to chronic irritation and inflammation
• NTP Study: A study by the National Toxicology Program (NTP) on a mixture of toluene 2,4- and 2,6-diisocyanate administered by gavage showed an increase in tumours of subcutaneous tissues in male and female rats, the pancreas in male rats, the mammary gland and liver in female rats, and the liver and circulatory system in female mice.

Safety

First Aid Measures

• Eye Contact: Rinse eyes with lukewarm water for at least 15 minutes; seek medical attention.
• Skin Contact: Wash with soap and water; remove contaminated clothing; seek medical help if irritation develops.
• Inhalation: Move to fresh air; seek immediate medical attention.
• Ingestion: Do not induce vomiting; rinse mouth with water and seek medical help.

Exposure Controls & Personal Protection

Engineering Controls

• Use local exhaust ventilation to keep airborne TDI levels low.
• Regular monitoring of air quality is recommended to ensure TDI levels remain within safe exposure limits.

Personal Protective Equipment (PPE)

• Respiratory: Wear respiratory protection when ventilation is insufficient.
• Gloves: Nitrile, butyl rubber, neoprene, or PVC gloves provide good resistance.
• Eye Protection: Safety goggles or full-face shields.
• Clothing: Wear protective clothing to minimise skin exposure.

Regulations

United States

Australia

Safe Work Australia lists the following exposure standard:

• 0.02 mg per cubic metre (0.00002 grams per cubic metre), on a time-weighted average basis (TWA) 
• 0.07 mg per cubic metre (0.00007 grams per cubic metre), for short-term exposures (STEL)