Note: The EPA is in the process of tightening the following regulations:
Environmental Protection Agency (EPA) Cr6+ Clean Air Act
While the quality of air that workers breathe inside a plant is regulated by OSHA PELs, hazardous contaminants released into the outside environment in the US are an EPA concern. Under the Clean Air Act, the EPA has issued a NESHAP (national emission standard for hazardous air pollutants) for chromium compound emissions from hard and decorative chrome plating and chromic acid anodizing processes. About two-thirds of the emissions from all chromium sources are in the form of Cr6+. The rule was originally promulgated in 1995 and amended in 2004.
Hard chrome plating
The EPA air emission limit for Cr6+ from hard chrome plating facilities is:
- 0.015 mg m-3 (15 µg m-3) of dry standard exhaust air from all tanks in a “large” facility or newer (installed after 1993) “small” facility
- 0.03 mg m-3 (30 µg m-3) of dry standard exhaust air from all tanks in an older small facility.
A facility is designated “large” or “small” when the rectifier capacity for all hard chrome plating tanks is greater or less than 60 million ampere-hours per year, respectively. If the plating tanks are enclosed, the EPA rule allows an alternate emission limit involving a calculation based on tank surface area. For tanks that use a chemical fume suppressant containing a wetting agent to reduce misting of the plating bath, compliance with the emission limit can be achieved by maintaining the surface tension of the bath below certain levels. Cleaning and rinse tanks are exempt from the rule altogether.
Decorative chrome plating and chromic acid anodizing
EPA restrictions on emissions of Cr6+ and Cr3+ from decorative chrome plating or chromic acid anodizing tanks are much simpler than those for hard chrome plating. The emission limit for Cr6+ from all chromic acid decorative chrome or anodizing tanks is 0.01 mg m-3 (10 µg m-3) of dry standard exhaust air, but control of the bath surface tension is all that is necessary when a fume suppressant with a wetting agent is used – which is also one of the possible methods for controlling Cr6+ emissions from hard chrome plating. For decorative chrome plating from a Cr3+ bath, the only requirements are keeping of records and reporting.
The original EPA chrome plating and chromic acid anodizing regulation required all platers and anodizers subject to the NESHAP to obtain a Title V operating permit under the Clean Air Act – often a costly and burdensome process. While this requirement still applies to major emission sources (those that emit more than 10 tons of chromium or more than 25 tons of any hazardous pollutant mixture per year), all smaller sources are permanently exempt under an amendment to the regulation proposed in 2005. Decorative chrome platers using fume suppressants or wetting agents had been granted a previous exemption.
Apart from surfactants, the techniques most commonly used to control emissions of chromium from plating and anodizing tanks involve scrubbers or mesh pads. In addition to emissions control, the EPA rule regulates initial testing, work practices, compliance monitoring (required daily), record keeping (including excess emissions), and reporting.
Note: EPA plans to regulate PFOS surfactants out of the market in the near future. Short chain fluorinated polymers will still be allowed but long chain sufactants used in today’s industry are being regulated out of existence.