Degreasers, occupational exposure

The Occupational Exposure Standards imposed for trichloroethylene are Maximum Exposure Limits of 100 ppm (8 hr TWA) and 150 ppm (15 minute reference period). A skin notation Sk is applicable because of the potential for skin absorption. Because of its volatility, trichloroethylene is not recommended for cold cleaning it is normally used in partially enclosed vapour degreasing equipment provided with local exhaust ventilation. 

Workers involved in the manufacture or use of trichloroethylene as a metal degreaser or general solvent may constitute a group at risk because of the potential for occupational exposure. Occupational exposure to trichloroethylene may also occur during its use as a chemical intermediate in the production of polyvinyl chloride (McNeill 1979). 

According to the 1990-93 CAREX database for 15 countries of the European Union (Kauppinen et al., 1998) and the 1981-83 United States National Occupational Exposure Survey (NOES, 1997), approximately 70 000 workers in Europe and as many as 100 000 workers in the United States were potentially exposed to carbon tetrachloride (see General Remarks). Occupational exposure to carbon tetrachloride may occur in the chemical industry, in laboratories, and during degreasing operations. 

Option A Use of local exhaust ventilation (LEV) to minimise occupational exposure via inhalation during metal degreasing. 

Prolonged TCE exposure has been associated with impairment of peripheral nervous system function, persistent neuritis and temporary loss of tactile sense and paralysis of the fingers after direct solvent contact. Chromosomal effects have been reported in those involved in the use of TCE for degreasing and symptoms of systemic lupus erythematosis have been reported after chronic TCE exposure. In addition, organic dementia has been noted after occupational exposure to TCE and there have been some reports of an association between exposure and scleroderma, an autoimmune disease. 

Table 10.7 compares the degreasing efficacy and various EHS properties of three dimethylamides of natural fatty acids with different chain lengths, trichloroethylene, and the average value for traditional solvents. Because of the low vapour pressure, the VOC emission potential is very low and the occupational exposure and flash point reach safer values. As they are based on natural vegetable oils, the alternative solvents exhibit a high renewable mass index. 

Yanez-Diaz et al. (1992) presented two male patients with SSc and pulmonary silicosis after occupational exposure to silica, and one of them to trichloroethylene as a degreasing agent. The clinical and analytical findings could not be distinguished from those present in idiopathic SSc except the chest X-ray with interstitial images featuring calcified hilar lymph nodes suggestive of pulmonary silicosis. 

Trichloroethylene is a versatile chemical compound used extensively in vapour degreasing of metals, and to a more limited degree, as a solvent for dry-cleaning and for adhesives. Although the major rate of elimination of trichloroethylene, regardless of the method of exposure, in the rat is by exhalation through the pulmonary system (Daniel 1963), in man the nephrotoxic and genotoxic N-acetyl-S-dichlorovinyl-L-cysteine as an urinary metabolite was found after occupational exposure to 1,1,2-trichloroethylene (Birner et al. 1993). 

In order to judge the level of risk involved, a number of factors must be considered. These include the quantity of the substance used or produced, how often it is worked with, how hazardous it is and whether exposure is likely to exceed the occupational exposure standard (if one is listed). For example, a degreasing agent, paint or an adhesive containing solvent may be relatively harmless when being used in the open air, but in a confined space with poor or no ventilation, significant exposure to it may be life-threatening. 

There are a wide variety of solvents used in industrial processes, and exposure can also occur in other occupational settings such as laboratories and workshops. Solvents can have toxic effects ranging from narcosis, irritation, and degreasing of skin to effects on major organs such as the central nervous and reproductive systems. The trend of inhaling solvents, for their narcotic effects, which became popular in teenagers will be discussed on p. 198. 

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