Workplace Emission Factors for Hexavalent Chromium Plating

Abstract

Effective control of emissions from electroplating is necessary to maintain a healthy workplace. However, in many cases the emission rates are not well characterized. This study describes a methodology to determine such rates with application to a hexavalent chromium plating line under production conditions. Area concentrations were determined from particulate samples collected on open-face filters using calibrated personal sampling pumps. Twelve sets of 1-hour samples were collected at six locations at different distances from the plating tanks and in the hood of the local exhaust system. The filters were analyzed using proton-induced X-ray emission spectroscopy. For each 1-hour period, measurements of area concentrations were transformed to emission rates by using a multipoint diffusion mass balance model in conjunction with measured ventilation rates. In addition, source activities such as area plated, ampere-hours consumed, and total power usage were recorded simultaneously with concentration measurements. Comparison of the emission rates with source activities allowed us to determine emission factors as well as the emission rates. The hood emission results were in good agreement with hood emissions measured in a California Air Resources Board study of hard chrome plating (which did not measure workroom emissions). The workroom emissions were related to plating line throughput such as total area plated or ampere hour of plating current, which was consistent with results from a previous study on another hexavalent chromium line. The emission factors for hood and workroom were 0.0805 and 2.57 ċ 10⁻⁴ mg/A ċ h, respectively. The methods provide a first estimate for determining workroom emissions when no other data are available, and are a useful way to extend field test measurements. For systems with local exhaust ventilation the approach also allows determination of mass-based collection efficiency, in this case an average of 99.1 percent based on hourly average emission rates.