Toluene diisocyanate exists in two isomeric forms (2,4-toluene diisocyanate and 2,6-toluene diisocyanate), which have similar properties and effects. Toluene diisocyanate is produced commercially as an 80:20 (2,4-toluene diisocyanate:2,6-toluene diisocyanate) mixture of the two isomers. At room temperature, the mixture is a clear, pale yellow liquid with a sharp, pungent odor. It should be stored under refrigeration, away from light and moisture in a tightly closed container in an inert atmosphere. Toluene diisocyanate is insoluble in water and miscible with most common organic solvents.

Toxicity Data
LD50 oral (rat) 4130 mg/kg
LD50 skin (rabbit) >10 g/kg
LC50 inhal (rat) 14 ppm/4 h (100 mg/m3; 4 h)
PEL (OSHA) 0.02 ppm(ceiling 0.14 mg/m3)
TLV-TWA (ACGIH) 0.005 ppm (0.036 mg/m3)
STEL (ACGIH) 0.02 ppm (0.14 mg/m3)

Major Hazards
Sensitizer by inhalation and skin contact; possible human carcinogen (OSHA "select carcinogen").

Acute Health Effects
Swallowed

• Accidental ingestion of the material may be seriously damaging to the health of the individual; animal experiments indicate that ingestion of less than 40 gram may be fatal.

Eye

• There is evidence that material may produce eye irritation in some persons and produce eye damage 24 hours or more after instillation. Severe inflammation may be expected with pain.
• Irritation of the eyes may produce a heavy secretion of tears (lachrymation).

Skin

•  The material may cause moderate inflammation of the skin either following direct contact or after a delay of some time. Repeated exposure can cause contact dermatitis which is characterized by redness, swelling and blistering.
• Skin contact with the material may damage the health of the individual; systemic effects may result following absorption.
• Open cuts, abraded or irritated skin should not be exposed to this material.
• Entry into the blood-stream, through, for example, cuts, abrasions or lesions, may produce systemic injury with harmful effects. Examine the skin prior to the use of the material and ensure that any external damage is suitably protected.

Inhaled

•  The material can cause respiratory irritation in some persons.

The body's response to such irritation can cause further lung damage.

• The vapor/mist may be highly irritating to the upper respiratory tract and lungs; the response may be severe enough to produce bronchitis and pulmonary edema. Possible neurological symptoms arising from isocyanate exposure include headache, insomnia, euphoria, ataxia, anxiety neurosis, depression and paranoia.
• In addition to producing pulmonary sensitization, toluene diisocyanate (TDI) is active in contracting smooth muscle such as that found in the airway.

So-called bronchoconstriction is often mistaken for sensitization and lung function tests, including measurement of forced expiratory volume (FEV1) and forced vital capacity (FCV) may distinguish acute reaction.

Health Hazard
Toluene-2,4-diisocyanate is a highly toxic compound by inhalation, a skin and eye irritant, and a carcinogenic substance. Exposureto its vapors can cause tracheobronchitis, pulmonary edema, hemorrhage, and death. Thetarget organs are the respiratory system andskin. The toxic effects were also noted in theliver, kidney, and gastrointestinal tract. In humans, exposure to low concentrations, 0.1–0.2 ppm, can result in irritation of the eyes, nose, and mucous membranes.Acute exposure to higher concentrationscan cause bronchitis, pneumonitis, headache,sleeplessness, pulmonary edema, and sometimes an asthma-like syndrome. Chronicexposure can result in wheezing, coughing,shortness of breath, and chest congestion.Such effects may be manifested from inhalation of 0.02–0.05 ppm of the diisocyanateover a period of time. Acute oral toxicity of this compound,however, is low. Symptoms may be coughing, vomiting, and gastrointestinal pain.Absorption through skin can produce toxiceffects similar to those of inhalation toxicity:bronchitis, pulmonary edema, and asthma. Inaddition, the acute toxic symptoms can benausea, vomiting, abdominal pain, dermatitis, and skin sensitization. Contact with eyescan cause burning, lacrimation, prickling type sensation, and injury to vision.

Toxicity
The acute toxicity of toluene diisocyanate by inhalation is high. Exposure to TDI can cause lung damage and decreased breathing capacity. Symptoms of exposure may include coughing, tightness of the chest, chest pain, nausea, vomiting, abdominal pain, headache, and insomnia. TDI irritates the skin, and eye contact can cause irritation with permanent damage if untreated. The oral acute toxicity of this substance is low. The odor of TDI does not provide an adequate warning to avoid overexposure.
Toluene diisocyanate has caused sensitization of the respiratory tract, manifested by acute asthmatic reaction upon return to work after a period of time away from exposure. Initial symptoms include coughing during the night, with difficult or labored breathing. Skin sensitization can also occur. Toluene diisocyanate is listed in IARC Group 2B ("possible human carcinogen"), is listed by NTP as "reasonably anticipated to be a carcinogen," and is classified as a "select carcinogen'' under the criteria of the OSHA Laboratory Standard.

Flammability and Explosibility
TDI is a combustible liquid (NFPA rating = 1). Explosive limits in air are 0.9 to 9.5% by volume. Carbon dioxide or dry chemical extinguishers should be used for TDI fires.

Reactivity and Incompatibility
Contact with strong oxidizers may cause fires and explosions. Contact with water, acids, bases, and amines can lead to reactions that liberate heat and CO2 and cause violent foaming and spattering. TDI will attack some forms of plastic, rubber, and coatings.

Storage and Handling
Because of its high toxicity, carcinogenicity, and ability to cause sensitization, toluene diisocyanate should be handled using the "basic prudent practices", supplemented by the additional precautions for work with compounds of high toxicity. In particular, work with TDI should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact.

Accidents
In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. In case of eye contact, promptly wash with copious amounts of water for 15 min (lifting upper and lower lids occasionally) and obtain medical attention. If TDI is ingested, obtain medical attention immediately. If large amounts of this compound are inhaled, move the person to fresh air and seek medical attention at once.
In the event of a spill, remove all ignition sources, soak up the TDI with a spill pillow or absorbent material, place in an appropriate container, and dispose of properly. Respiratory protection may be necessary in the event of a large spill or release in a confined area.

Disposal
Excess TDI and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.