Health data and legal suits are causing Occupational Safety and Health Administration (OSHA) regulators to consider lowering the hexavalent chromium exposure limit. It is anticipated that future exposure limits could be established at levels between 20- and 200-fold below the current level of 52 micrograms per cubic meter (µg/m3) as chromium. At present, hexavalent chromium emissions from hard chromium electroplating baths are controlled by ventilation of the workplace, extraction fans, and use of an air pollution control device (APCD), which is typically a mist eliminator/wet scrubber, to remove chromium from the exhaust air stream. The Environmental Protection Agency (EPA) regulates emissions of hexavalent chromium to the outside atmosphere. This project investigated a 0.25 percent addition of a perfluorinated compound named Fumetrol® 140, a third generation wetting agent/fume suppressant (WA/FS), to hard chromium electroplating baths at the Naval Aviation Depot in Cherry Point, North Carolina and at the Oklahoma City Air Logistics Center at Tinker Air Force Base, Oklahoma.

Technology Description

Hexavalent chromium electroplating baths generate gases (i.e., hydrogen and oxygen) at the electrodes, which rise and create a mist of chromic acid as they burst at the surface. A WA/FS decreases the surface tension of a plating bath, which reduces the size of the bubbles and diminishes their impact as they escape at the surface. As a consequence, emissions of hexavalent chromium and worker exposure are greatly reduced. Fumetrol® 140 is relatively soluble in water and produces very little foam, making it easy to use.

Demonstration Results

Worker exposure to hexavalent chromium emissions was reduced. Air quality was approximately two to four times better with Fumetrol® 140 addition. However, even without Fumetrol® 140 addition, the most stringent proposed OSHA standard of 0.5 µg/m3 chromium was never exceeded. There was a 20- to 70-fold reduction in total chromium emissions in the exhaust air stream when the Fumetrol® 140 was used. In most cases, the exhaust chromium concentration was below the 30 µg/m3 chromium standard for small, existing tanks but did not attain the 15 µg/m3 chromium standard for new tanks. No adverse effects on the quality of the electroplated chromium or the steel alloys on which it was deposited were detected.

Implementation Issues

An average savings of $2,000 per year per tank was estimated for chromic acid that does not escape. Ventilation rates and associated energy costs would be reduced, and fewer or smaller APCDs might be necessary for a new electroplating plant. Wastewater treatment costs would also be reduced if an APCD were no longer required. For an existing system, the payback period on the minimal modifications necessary would range from under 7 months (if the APCD were turned off) to less than three years (if the APCD remained in use). In the future, it is possible that the EPA may consider allowing the control of hard chromium electroplating tank emissions through the use of a WA/FS alone, which would only require surface tension measurements for monitoring. (Project Completed - 2003)