Tuesday, May 17, 2016


Hydrocarbons are organic compounds made primarily of carbon and hydrogen atoms. The addition of chlorine to the carbon-hydrogen chemical backbone increases the stability and decreases the flammability of the resulting compounds. Chlorinated hydrocarbon compounds are a diverse group of compounds, some of which are widely used in industrial and leisure activities. Common chlorinated hydrocarbons include carbon tetrachloride, methylene chloride, and trichloroethylene. These solvents have characteristic slightly pungent odors. They are used extensively in industry as cleaning, degreasing, and thinning agents because of their excellent solvent properties and low flammability relative to other effective solvents. They are also used in the manufacture of other chemicals including plastics and pesticides. Because of their high volatility and low boiling point, workplace exposures may be greater than anticipated. At high temperatures, these substances may decompose to yield highly toxic gases such as phosgene and hydrogen chloride. They are commonly encountered as mixtures with variable toxicity depending on the concentration of individual constituents.

Carbon tetrachloride is used infrequently due to its relative potency as a liver and kidney toxin. Methylene chloride (dichloromethane) is a common constituent of paint strippers, is very volatile, and can accumulate substantial amounts in enclosed spaces; it is metabolized to carbon monoxide and results in elevated carbon monoxide levels extending about 2.5 times longer than with carbon monoxide inhalation. In a small number of people, trichloroethylene will produce "degreaser's flush," a transient reddening of the face and neck, which occurs when the individual consumes even small quantities of alcohol. Sometimes this reaction may also produce a sensation of fullness in the chest and breathlessness.

As a class, the chlorinated hydrocarbons are potent central nervous system depressants or stimulants. They also cause greater liver and kidney damage compared to other organic solvents. Many have been shown to cause cancer in laboratory animals; due to widespread industrial use, the issue of carcinogenic risk to humans is one of the most controversial issues in regulatory toxicology. The chlorinated hydrocarbons have been implicated in causing sudden death at high exposure levels possibly related to the development of heart arrhythmias (ventricular fibrillation).

Exposure to chlorinated hydrocarbon compounds in the occupational setting is primarily through inhalation. Skin absorption is variable and usually insignificant, although dermal absorption following prolonged or extensive skin contact can cause systemic toxicity.

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