|Occupational Health and Safety
Hazardous Substances: Isocyanates
Isocyanates are used to make flexible and rigid polyurethane foams, elastomers, adhesives, sealants and coatings such as
polyurethane paints, varnishes and wire enamels. Isocyanates can adversely affect your health if inhaled, if they come in contact
with the eyes or skin and if swallowed. Most toxic effects reported have been due to toluene diisocyanate (TDI) as it used to be the
most commonly used isocyanate, but other kinds of isocyanates can cause problems similar to those caused by TDI. Other
isocyanates are methyl isocyanate (MIC), methylene diphenyl diisocyanate (MDI), dicyclohexyl methane diiasocyanate
(hydrogenated MDI;HMDI), hexamethylene diisocyanate (HDI), naphthalene diisocyanate (NDI), isophorone diisocyanate (IPDI) and
polymethylene polyphenol isocyanate (PAPI). The most commond ones are TDI and MDI, with MDI becoming steadily more common
as it is less hazardous and less volatile (evaporates less) than TDI.
Isocyanates are very strong irritants. TDI and HDI are volatile and cause respiratory irritation more often than do the less volatile
MDI and NDI, except when the latter are heated or inhaled as a mist. HMDI rarely causes respiratory effects but is more likely to
cause skin irritation than are other isocyanates.
Injury initially happens to areas of direct contact such as the eyes, nose, mouth and respiratory tract. At low exposure levels,
isocyanates cause eye and nose irritation, dry or sore throat, runny nose, shortness of breath, wheezing and laryngitis at low
exposure levels. Coughing, chest pain and a tight feeling in the chest may also occur, particularly at night. These symptoms may not
show up until several hours after exposure occurs. High exposures can cause inflammation of the lung tissue (chemical
pneumonitis), bronchitis, severe wheezing as with asthma, severe coughing spasms and accumulation of fluid in the lungs
(pulmonary edema). Pulmonary edema must be considered as a medical emergency condition since it can lead to death. Rapid
deaths following exposure to high concentrations and delayed deaths resulting from exposures to lower concentrations of methyl
isocyanate (MIC) have occurred because of injury to the respiratory system.
Euphoria, loss of muscle coordination and loss of consciousness may occur after a single high exposure to TDI. Headache, difficulty
in concentration, poor memory and confusion may occur and these effects can last for as long as four years. Exposure of the eyes to
liquid isocyanate or mist can cause watering of the eyes, severe irritation and may cloud the cornea resulting in reduced vision.
Should isocyanates be swallowed for some reason, they cause irritation and corrosion of the tissues lining the mouth, throat and
See also the information on sensitization in the following section.
Skin: Prolonged or repeated skin contact with isocyanates causes severe inflammation, redness, rash, swelling, blistering, burns,
skin discolouration and hardening of the skin.
Sensitization: TDI is a sensitizer, which means that it causes allergic reactions of the skin and lungs in some people. Other
isocyanates may be sensitizers as well. Sensitization is usually caused by one very large exposure or by repeated small exposures.
Sensitized people react to very low levels of isocyanates that have little effect on non-sensitized people. Once a person is
sensitized contact with even a small amount of isocyanate can cause outbreaks of dermatitis (skin redness, rash, itching and
swelling), which can spread all over the body. Some people who inhaled TDI developed extensive skin rashes that lasted up to a
week and a half, even though they had no direct skin contact with the substance. Cross-sensitization between different
isocyanates can occur, e.g. someone hypersensitive because of exposure to TDI may also react to MDI and HDI.
Lungs: Repeated exposure to MDI at levels in air too low to cause obvious symptoms may nevertheless result in permanent lung
damage. Isocyanates can cause lung allergies. The symptoms at first resemble those of a cold or hay-fever but the problem may
progress to serious asthma-like symptoms such as wheezing, chest tightness, shortness of breath, difficulty breathing and
coughing. Fever, chills, general feelings of discomfort, headache, and tiredness can also occur. These symptoms can occur right after
exposure or they may occur several hours after exposure. The symptoms go away when the worker leaves the workplace for a few
days (e.g. on weekends or vacations), but they occur again the next time the person is exposed. Some sensitized individuals have
died after accidental exposure to relatively low concentrations of TDI. Respiratory sensitivity may result from exposure of the skin,
not only from breathing it in. Recovery depends on the individual; some sensitized workers may experience adverse health effects
for years after exposure, while others recover within months provided exposure doesn’t occur again.
TDI and MDI can cause asthma, and some workers who develop isocyanate asthma become hypersensitive to other substances.
TDI and MDI can also cause an allergic lung disease called hypersensitivity pneumonitis or extrinsic allergic alveolitis. Symptoms of
this disease include shortness of breath, fever, malaise, non-productive cough, and chills. Other isocyanates probably cause these
problems as well, but since they’re not used as commonly as TDI and MDI there isn’t as much evidence for this, yet. Exposure to
isocyanates causes added distress to those with existing respiratory disease such as chronic bronchitis and emphysema.
Reproduction: There is evidence that MIC may increase the frequency of miscarriages among pregnant women, damage the
developing fetus and decrease fertility of men and women. Much of this evidence comes from the aftermath of the 1984 disaster in
Bhopal, India where MIC was released in an explosion at a Union Carbide pesticide plant.
Cancer: One type of isocyanate, 2,6-toluene diisocyanate (2,6-TDI) is an animal carcinogen and a possible human carcinogen.
Local exhaust ventilation
Personal protective equipment.
Do not smoke, eat or drink in work areas
Wash hands thoroughly after handling these materials.
Remove contaminated clothing promptly, keep contaminated clothing in closed containers, discard or decontaminate and launder
them before rewearing, decontaminate contaminated clothing before laundering by soaking for an hour in decontaminant solution.
“TDI” may be a mixture of 2,4-TDI and 2,6-TDI. 2,6-TDI is a possible human carcinogen. All carcinogens should be eliminated from
the workplace wherever possible as every dose increases the risk of contracting cancer. This is because even minimal amounts of
carcinogen can initiate the uncontrollable growth of abnormal cells.
2,4-TDI: ACGIH TLV 0.005 ppm (0.036 mg/m3).
MDI: ACGIH TLV 0.005 ppm (0.051 mg/m3).
Source: CAW Health, Safety & Environment Department