Diisocyanates skin irritation

Mobay Corporation. 1981b. The evaluation of hexamethylene-1,6-diisocyanate for primary skin irritation in rabbits. EPA/OTS doc 86-870001242. 

MDI is an eye and skin irritant. Contact with skin can produce eczema. The acute oral toxicity of this compound is very low, considerably lower than that of toluene-2,4-diisocyanate. The lethal dose for rats was... 

Volatile isocyanates, such as TDI and hexamethylene diisocyanate, are irritants to the eyes, nose and throat. Higher molecular weight polyisocyanates for paints therefore should contain very low levels of these isocyanates, so that the isocyanate content of the air around them remains below the threshold limit value (see p. 124). Even if they contain only low levels of volatile isocyanates, precautions must be taken to prevent inhalation of spray droplets containing unreacted isocyanates (either excellent extraction of overspray in the spray booth, or the wearing of fresh air hoods by those in the vicinity). The uncured liquid finishes can also be skin irritants. 

Aliphatic diisocyanates can have strong, adverse skin irritation effects and two are well known for this problem, namely dicyclohexylmethane diisocyanate (H12MDI) (Desmodur W by Bayer) and hexamethylene diisocyanate (HDI). Usually care in handling and good hygiene prevents undue problems. Occasionally a more serious effect has been observed in one instance a chemical worker exposed her face to the hot vapour of dicyclohexylmethane diisocyanate and within 24 h her head had swollen to 20% of its original size and characteristic red spots with a white centre were present over the exposed area. Recovery took place slowly over a period of 3 weeks with cortisone-type ointment treatments. Her central nervous system was also affected and took some months to become normal. This was a very unusual and unique incident and is recorded to show that occasionally the unexpected human response can occur with diisocyanates. 

Skin irritation can also be caused by amine accelerators, e.g., MDA (van Joost et al. 1987), triethylene-diamine (Adams 1983) and triethylamine (Malten 1964). Concentrated liquids may even be corrosive. The irritant effect of diisocyanates in the hardeners, glues and paints may also be attributed to the solvents used in these products. Completely hardened PU products usually do not cause skin problems. However, some unreacted isocyanate monomer may remain in surplus inside the PU foam, even after curing. During machining and cutting, PU dust containing isocyanate is produced. When heated to above 250 °C, PU polymers decompose into isocyanates and nitrogen oxides, and may then cause dermatitis (Bjorkner 1992). 

Toxicology. Hexamethylene diisocyanate (HDI) is an irritant of the eyes, mucous membranes, and skin and is a sensitizer of the respiratory tract. 

Toxicology. Isophorone diisocyanate (IPDI) is an irritant and sensitizer of the respiratory tract and the skin. 

Irritant dermatitis does not involve an immune response and is typically caused by contact with corrosive substances that exhibit extremes of pH, oxidizing capability, dehydrating action, or tendency to dissolve skin lipids. In extreme cases of exposure, skin cells are destroyed and a permanent scar results. This condition is known as a chemical burn. Exposure to concentrated sulfuric acid, which exhibits extreme acidity, or to concentrated nitric acid, which denatures skin protein, can cause bad chemical bums. The strong oxidant action of 30% hydrogen peroxide likewise causes a chemical bum. Other chemicals causing chemical bums include ammonia, quicklime (CaO), chlorine, ethylene oxide, hydrogen halides, methyl bromide, nitrogen oxides, elemental white phosporous, phenol, alkali metal hydroxides (NaOH, KOH), and toluene diisocyanate. 

The toxicity of aliphatic diisocyanates also warrants monitoring exposure to its vapors. HDI has a moderate potential for acute systemic dermal toxicity rabbit dermal LD50 is 570 ml/Kg (57). However, HDI is severely irritating to the skin and eyes. Irritation, lacrimation, rhinitis, burning sensation to throat and chest, and coughing have all been reported in humans following acute inhalation exposure to HDI. HMDI has a low eye and dermal irritation potential, as well as a low potential for acute toxicity. Exposure to HMDI aerosol can cause dermal sensitization of laboratory animals. IPDI can cause skin sensitization reactions as well as eye irritation. The acute toxicity of diisocyanates in rats is shown in Table 12. 

NIOSH REL (Diisocyanates) TWA 0.005 ppm CL 0.02 ppm/lOM DOT CLASSIFICATION 6.1 Label KEEP AWAY FROM FOOD DOT Class 6.1 Label Poison DOT Class 6.1 Label Poison, Flammable Liquid DOT Class 3 Label Flammable Liquid, Poison SAFETY PROFILE Poison by inhalation. Mildly toxic by ingestion. Human systemic effects by inhalation increased immune response and body temperature. A skin and eye irritant. An allergic sensitizer. Questionable carcinogen. Mutation data reported. A flammable liquid. When heated to decomposition it emits toxic fumes of NOx and SOx. See also CYANATES. 

Diisocyanates are an important class of chemicals of commercial interest, which are frequently used in the manufacture of indoor materials. such as adhesives, coatings, foams and rubbers (Ulrich, 1989). In some types of particle board, the diisocyanates have replaced formaldehyde. Isocyanates are characterized by the electrophilic -N=C=0 group, which can easily react with molecules containing hydroxy groups, such as water or alcohols. On hydrolysis with water, primary amines are formed, while a reaction with alcohols leads to carbamates (urethanes). Polyurethane (PUR) products are then obtained from a polyaddition of diisocyanate and diol components. Compounds commonly used in industrial surface technology are 4,4 -diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI). The diisocyanate monomers are known as respiratory sensitizers and cause irritation of eyes, skin and mucous membrane. Therefore, polyisocyanates such as HDI-biuret and HDI-isocyanurate with a monomer content <0.5 % are used for industrial applications, and isocyanate monomers will not achieve high concentrations in ambient air. Nevertheless, it is desirable to measure even trace emissions from materials in private dwellings. 

Toluene-2,4-diisocyanate is a highly toxic compound by inhalation, a skin and eye irritant, and a carcinogenic substance. Exposure to its vapors can cause tracheobronchitis, pulmonary edema, hemorrhage, and death. The target organs are the respiratory system and skin. The toxic effects were also noted in the liver, kidney, and gastrointestinal tract. 

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. 

Example 5. Toluene diisocyanate (TDI) has an LD50 (rat, oral) = 2060 mg/kg, which places it in HC 5 with regard to ingested toxicity. However, the LC50 (various animals) = 0.06-0.35 mg/L (4 h), which places it in HC 1 for inhaled toxicity. Furthermore, it is described as a powerful irritant to eyes, skin, and the respiratory tract, which places it in HC 1 for skin corrosive, respiratory sensitizer, and eye damage. Clearly, many precautions must be taken when working with TDI. 

Urethane resins may contain free diisocyanates, which are usually respiratory irritants and sensitizers that have caused rhinitis and asthma (Estlander et al. 1992). 2,4-toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI) are important respiratory sensitizers, whereas 4,4 -diphenylmethane diisocyanate (MDI) is the most important skin sensitizing diisocyanate (Estlander et al. 1992). Two-component systems in which addition of a diisocyanate to the polyhydroxyl compound immediately before use carry the greatest risk of skin sensitization. Partial polymerization of diisocyanates to increase molecular weight and reduce volatility are used to decrease the risk of sensititization (Mathias 1984). See also the chapter on polyurethane resins in this book. 

Hexamethylene diisocyanate is a liquid with a volatility of the same order as that of tolylene diisocyanate. It is a respiratory irritant and also has powerful effects on the skin and eyes. Hexamethylene diisocyanate was one of the first diisocyanates utilized for making polyurethanes, being used to prepare fibreforming polymers it now finds limited use in the preparation of moulding materials. 

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