Hazard evaluation and technical assistance report, HETA-2000-0041-2796, OmniSource Corporation, precious metal recycling facility, Ft. Wayne, Indiana.
On November 1, 1999, the National Institute for Occupational Safety and Health (NIOSH) received a management request from OmniSource Corporation to conduct a health hazard evaluation (HHE) to evaluate occupational exposure to silver at their company’s precious metal recycling (PMR) facility in Ft. Wayne, Indiana. The request was prompted by concerns about one employee who had been diagnosed as having argyria, a blue-grey discoloration of the skin, mucous membranes, and/or eyes resulting from prolonged silver exposure. Management also expressed concern about worker exposure to the fixer solution from which the silver is recovered. A site visit, conducted on January 10-11, 2000, consisted of an environmental and medical component. The environmental evaluation included a full-shift personal breathing-zone (PBZ) air sample to assess worker exposure to silver and 26 other metals and minerals and full-shift area air sampling to assess exposure to 26 different metals and minerals, glutaraldehyde, hydroquinone, and hydrogen cyanide. Qualitative ventilation measurements were also performed to determine airflow patterns. The medical evaluation consisted of a record review, employee interviews to assess a medical and occupational history, and focused physical examinations of each of the three PMR facility employees. The one full-shift PBZ sample taken on an operator revealed a time-weighted average (TWA) silver exposure of 0.14 milligrams per cubic meter (mg/m3 ), 14 times greater than the Occupational Safety and Health Administration (OSHA) and NIOSH exposure limit of 0.01 mg/m3 . Full-shift area air sampling revealed silver concentrations ranging from 0.009 to 0.19 mg/m3 . All area samples, with the exception of one, had concentrations that exceeded the OSHA and NIOSH exposure limits. The PMR facility furnace operator wore a half-mask powered air-purifying respirator (PAPR) in the furnace room and main PMR facility; however, respirators were not worn when employees were in the work station and office area, where silver concentrations ranged from 0.012 to 0.02 mg/m3 . These levels exceed OSHA and NIOSH exposure limits. Full-shift area air sampling for glutaraldehyde, hydroquinone, and hydrogen cyanide revealed no detectable amounts of those substances. None of the 26 other metals or minerals analyzed for in the air samples exceeded any applicable exposure limit. The qualitative ventilation assessment indicated that the furnace room was under strong negative pressure, that should prevent silver dust and fume from escaping the room. However, silver was detected in area samples taken throughout the rest of the facility, suggesting that silver is migrating from the furnace room to other areas. Neither exhaust hood (one was in place over each of the two working furnaces) was operating during our visit. Fumes off-gassing from the furnaces could periodically be seen escaping the hoods. During the loading and unloading of the crucibles, the furnace room doors are left open and airborne silver may escape the room. Pressure tests indicated the work station and office area to be under neutral pressure. It is also possible that the furnace operators are unknowingly transferring silver from their clothes, gloves, and shoes to other areas of the facility. Of the three workers interviewed, none revealed health effects thought to be related to exposures at OmniSource other than the one worker with a diagnosis of argyria. However, based on the history provided by the worker with the skin lesion, it is unlikely that the lesion represents localized argyria. NIOSH investigators concluded that employees in the PMR facility are overexposed to silver when powered air-purifying respirators (PAPRs) are not worn. Although the furnace room is under negative pressure, it appears that airborne silver may be escaping the furnace room and migrating to other areas of the PMR facility, including the work station and office area where respirators are not usually worn. Recommendations are offered in this report for improved exhaust ventilation, personal protective equipment, general safety, and housekeeping in the workplace to decrease worker exposures. Medical recommendations to assess the body burden of silver are also included.