Metal Finishing Guide Book

2013

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ENVIRONEMNETAL ISSUES Hexavalent chrome is a highly hazardous substance and proper knowledge of its nature is essential to maintain a safe workplace. The Occupational Health and Safety Act (see OSHA Hazard Communication Standard (29 CFR 1910.1200)) sets the limit of exposure as the Permissible Exposure Limit (PEL). It is the responsibility of each operation to assure that workers are not exposed beyond these limits. There is an action level at which point a plan must be developed to decrease exposure. More information is available on requirements through your supplier's material safety data sheet (MSDS) which should be kept on file and available to all personnel. Other regulations also give requirements for the use of hexavalent chrome for plating applications. These include the Clean Air Act and the Clean Water Act, which sets limits as to how much hexavalent chrome is allowed to be discharged to the outside by exhaust or by wastewater. These laws are enforced by the United States Environmental Protection Agency (EPA) who set the standards. A full discussion of the laws and their requirements is beyond the scope of this article, but a review of the section on Industrial Ventilation and Pollution Control would be beneficial. The section on Waste Water Treatment is also beneficial to understanding the requirements for plating in general. The use of stable surfactants as fume and mist control has been an acceptable means of controlling the mist generated during hexavalent chrome plating. The gases generated by the electrolysis from both the cathode and the anode reactions are high and carry droplets of the hexavalent chrome into the ambient air. These hazardous fumes and mist can be minimized to a significant degree by reduction in the surface tension through the use of these surfactants and in some applications may meet the requirements of OSHA and the USEPA. In addition to use of suppressants as a means of minimizing fumes and mist, it is also found to be beneficial in keeping air ventilation and scrubber systems low in contaminants and reduces down time, wear and maintenance. When using mist suppressants as a means of controlling copious amounts of foam formed by the generation of hydrogen and oxygen, gases can generate an explosive condition if a spark ignites the gases in the foam. This can lead to the foam containing the hazardous hex chrome to leave the confinement of the tank, possibly causing a danger to workers. Low foaming mist and fume suppressants are available and would be preferable to the foaming type that intentionally build the foam blanket to suppress the misting. There recently have been several articles covering the use of these type of mist and fume suppressants. One of these issue is the persistent, bioaccumulative and toxic (PBT) of some of the chemistries and in particular PFOS-based products used as mist/ fume suppressants. It is anticipated that chemicals that are non-PFOS containing with lower PBT will become available. It is anticipated that the PFOS types will be banned. On a global level, many countries have already eliminated the use of PFOS based products in all industries. 1Cr (III) is not the same as chromium trioxide 269

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