Metal Finishing Guide Book


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Page 61 of 903

SAFETY Unfortunately, one of the most overlooked aspects of industrial cleaning is safety. The use of chemicals for industrial cleaning exposes the user to potential injury if proper safeguards are not employed. The potential problems are well documented in Material Safety Data Sheets, books, and articles that have been written over the years. The warnings are of little value unless they are read, understood, and acted upon by those handling, using, or working in areas in which the chemicals are used. A summary of the safety aspects of chemical cleaning are as follows. Acids The use of acidic cleaners containing appreciable amounts of sulfuric acid can expose the worker to potential splashing due to exothermic reactions that can result in localized boiling. Additions should be made in a slow, controlled manner to prevent splashing and localized boiling. Acids should be added to water. Water should not be added to concentrated acids. Addition of acid cleaner concentrates to replenish working solutions should always be made to cool solutions (<100oF). Without exception, acid-resistant goggles, face shield, boots, apron, and gloves should be worn by workers to minimize the potential for body contact with the acidic solutions. Acid cleaners containing fluoride compounds can result in severe tissue damage. Precautions should be taken to avoid any contact with fluoride-containing solutions. If fluoride compounds are used, personnel should be trained in the treatment of fluoride burns. The use of acid cleaning compounds can result in the evolution of flammable and explosive hydrogen gas. Care should be taken to avoid uncontrolled release of pressure when parts are cleaned in sealed cleaning chambers. Sources of spark or flame that can ignite accumulated hydrogen should be identified and removed from the area in which acid cleaning is conducted. The use of acidic cleaners for cleaning sulfurized steel or parts that have sulfurized oil present can result in the generation of poisonous and flammable hydrogen sulfide gas. The same precautions employed for dealing with hydrogen evolution should also be employed for the potential evolution of hydrogen sulfide. Acid cleaner tanks and equipment should be properly vented to keep worker exposure to mists and vapors below OSHA limits. The reactivity of substrate material should be evaluated prior to acid cleaning to prevent violent reaction due to incompatibility and/or part damage. Alkaline Cleaners The use of alkaline cleaners containing strong alkaline compounds, such as sodium hydroxide and potassium hydroxide, can result in strong exothermic reactions when working solutions are made or replenished. Additions should be made to water or working solutions in a cautious, controlled fashion to prevent splashing and localized boiling. Additions should only be made to cool solutions (<100oF). Water should not be added to alkaline powders. The use of alkaline cleaners for etching or cleaning reactive metals, such as aluminum, zinc, or magnesium, will result in the evolution of flammable hydrogen gas that can accumulate in foam blankets or in enclosed cleaning equipment. Equipment should be ventilated and ignition sources should be removed from areas in which reactive metals are cleaned. 58

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