Metal Finishing Guide Book


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The high temperature of PCE vapors also permits complete and thorough drying of work by vaporizing moisture entrapped in porous metals, deeply recessed parts, and blind holes. Methylene chloride (MEC, also called dichloromethane) is a powerful and versatile chlorinated solvent known for its high solvency capabilities. MEC has the lowest boiling point (103.5��F, 39.7��C) and freezing point (-139��F, -95��C) of the chlorinated solvents, as well as the lightest vapor density (2.93 times that of air) and weight (10.98 lb/gal). Because of its low boiling point MEC is often used for degreasing sensitive parts such as thermal switches and thermometers, which would be damaged by high temperatures. It is also chosen when parts must be near room temperature after cleaning for immediate handling or for tolerance testing and measurements. These three solvents are widely used in surface cleaning, particularly in the vapor degreasing process. They are also used in cold cleaning, both dip and wipe methods, but the need to keep workplace vapor levels and environmental vapor losses low, in accordance with federal, state, and local regulations, limits their use in cold processes. HEALTH CONSIDERATIONS Health effects from exposure to chlorinated solvents have been studied extensively. Exposure to vapor concentrations within recommended guideline levels will not result in any known adverse effects on most people. Acute overexposure to vapors, however, may cause anesthetic or narcotic effects (solvent drunkenness) and death at high enough concentrations. Central nervous system effects and liver and/or kidney effects can result from chronic overexposure. Proper ventilation when using chlorinated solvents is essential. Because chlorinated solvent vapors are heavier than air, high concentrations can accumulate in poorly-ventilated and low-lying areas, such as pits, causing dizziness, unconsciousness, and eventually death. The chlorinated solvents have been subjected to a great many animal tests as well as epidemiological studies on humans to determine their health profile and so far the available scientific data indicate that they are not human carcinogens. On the basis of animal tests, however, the chlorinated solvents, like many other chemicals, have been given cancer classifications by different agencies. The U.S. EPA classes all three solvents as B2, ���Probable Carcinogen,��� while the American Council of Governmental Industrial Hygienists (ACGIH) classes PCE and MEC in Category A3, ���Animal Carcinogen,��� and TCE in Category A5 ���not suspected as a human carcinogen.��� All three solvents are listed under California's Proposition 65 as ���Known to the State of California to cause cancer.��� On the international scene the International Agency for Research on Cancer (IARC) places TCE and PCE in Group 2A, ���probably carcinogenic to humans��� and MEC in Group 2B, ���possibly carcinogenic to humans.��� The German MAK commission lists PCE and MEC in Category IIIB, ���possible carcinogen��� and TCE in Category IIIA, ���human carcinogen.��� WHAT REGULATIONS APPLY Users of chlorinated solvents for parts cleaning are aware of the regulations affecting the use, handling, transportation, and disposal of these solvents. They are regulated at the U.S. federal level under the Clean Air Act, the Clean Water Act, 106

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