Diisocyanates health hazards

US Environmental Protection Agency Generic Health Hazard Assessment of the Chemical Class Diisocyanates. Final Report. EPA Contract No. 68-02-3990. Washington, DC, US EPA, May 5, 1987... 

Free isocyanate vapors in the workplace are strictly controlled, because they are a health hazard. In the commercial production of prepolymers, the diisocyanates can be transferred in a closed system and the final prepolymer stripped of... 

Isoouanates. Various isocyanates are employed in the polymer industry. These compounds are powerful irritants and they are highly toxic. Of particular interest are methylene-di-paraphenylene isocyanate (MDI) and toluene-2,4-diisocyanate (TDI). Various alkyl isocyanates (e.g., methyl, ethyl, propyl, butyl, and cyclohexyl) derivatives may also be of current interest with respect to potential occupational health hazards. Simultaneous analysis of MDI and TDI by HPLC has been accomplished by a modification of the method of Dunlap et al. (28). Air samples are collected in impingers containing p-nitrobenzyl-n-... 

The toxicities of isocyanates vary widely. Methyl isocyanate is highly toxic, whereas dicyclohexyhnethane diisocyanate displays moderate action. In addition, health hazards differ significantly on the route of exposure. The toxicities of these isocyanates are discussed individually below. 

The toxic route is primarily inhalation. The vapor pressure of this compound at ambient temperature is very low, 0.00014 torr at 25°C. However, when heated to about 75°C, the acute health hazard is greatly enhanced (Hadengue and Philbert 1983). The acute toxic symptoms were found to be similar to those of toluene-2,4-diisocyanate and other aromatic isocyanates. Inhalation of its vapors or particulates can cause bronchitis, coughing, fever, and an asthma-like syndrome. Other symptoms were nausea, shortness of breath, chest pain, insomnia, and irritation of the eyes, nose, and throat. The immunologic response, however, varied among humans. Exposure to 0.1-0.2 ppm for 30 minutes is likely to manifest the acute toxic effects in humans. 

PU are compounds formed by reacting the polyol component with an isocyanate compound, typically toluene diisocyanate (TDI) methylene diisocyanate (MDI) or hexamethylene diisocyanate. Polyols are relatively non-toxic (i.e., polyether type polyols are found to be safe, because they are low in oral toxicity with almost no irritation effect to the eyes and skin), however, isocyanates are highly toxic and the product can have a significant toxicity if remnants of isocyanate are in it, which manifests itself mainly as a respiratory (as well as a dermal) hazard. Exposure to the vapour of isocyanates directly may cause irritation for the eyes, respiratory tract and skin. Such an irritation may be too severe to produce bronchitis and pulmonary oedema. As health hazards of isocyanates are considered, one immediately remembers one of the worst industrial disasters of the 20th century, that occurred in Bhopal, India, because of the toxic cloud of methyl isocyanate was released accidentally from the Union Carbide pesticide factory in December 1984. An estimated 3,000 people died immediately with a final of some 20,000, most suffocating from the cloud s toxic chemicals, and some 50,000 were injured, most were residents living near the plant. 

The following toxicological data on the health hazard effects of the two most commonly used diisocyanates, namely TDI and MDI, is now given for specific guidance. Inevitably much of this data relates to animal response studies which are not directly translatable into human responses. 

The general hazards to health associated with isocyanates may be summarized as follows all isocyanates (both aliphatic and aromatic) if present above certain critical values adversely affect the respiratory system. Surveys by the International Isocyanate Institute (which is primarily a voluntary association of isocyanate chemical manufacturers) suggest that normal individuals can work a standard 8-h day in an atmosphere in which the TLV of the diisocyanate is observed in recent years these values have been revised downwards (see Table 14.1).t However, mild to severe asthmatic attacks will result in the majority of people exposed to excessive inhalation of isocyanate vapour and this must be recognized as an acute hazard also loss of lung capacity and reduction in forced respiratory response results. Once an individual has suffered such an attack, some sensitization must, in the majority of cases, be assumed to have occurred ... 

The British Rubber Manufacturers Association (BRMA) publishes an operating and medical code of practice Isocyanates in Industry and the United Kingdom Health and Safety Executive publishes Isocyanates Toxic Hazards and Precautions, Environmental Hygiene No. 16 (1979). Additionally all isocyanate manufacturers provide free and excellent literature pertaining to the handling and use of diisocyanates. 

CAUTION The handling of isocyanates should be done with great care because of their known toxicity hazard. The hazards and chemistry of methyl isocyanate have recently been reported. Toluene diisocyanate (TDI), methylene diisocyanate (MDI), and methyl isocyanate (MIC) are flammable, very reactive, and have in common low maximum allowable concentrations for employee exposure by the Occupational Safety and Health Administration (OSHA). 

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