NIOSH Examines Metals, Minerals in Dust at Hydroelectric Dam

Published September 13, 2017

A new NIOSH report details the agency’s evaluation of occupational brake dust exposures at a hydroelectric dam. The request to NIOSH’s Health Hazard Evaluation (HHE) Program came from a safety manager at the dam who was concerned about employees’ exposures to metals and minerals in dust generated during the cleaning of brake and brush housings of hydroelectric turbine generators. NIOSH staff visited the dam during the scheduled shutdown of one of the dam’s three generators to evaluate brake dust cleaning activities. Agency investigators tested air, employees’ hands, and work surfaces for metals and minerals and evaluated the brake dust particles for size, shape, and elemental composition.

The minerals and metals identified in NIOSH’s dust samples were consistent with those listed on the dam’s safety data sheets. According to the agency, barium, calcium, chromium, magnesium, and manganese were the most abundant substances. NIOSH reports that employees’ airborne exposures to elements in brake dust were “well below their most protective [occupational exposure limits]” regardless of their work activity or location within the dam’s powerhouse.

“Our particulate sampling results showed that brake dust could escape from the interior of the turbine housing, but did not enter the employee control room or lunch room,” NIOSH’s report reads. “Employee hand cleaning practices, the availability of disposable clothing, and the use of sticky mats helped reduce the migration of contaminants from work areas to non-work areas.”

The dam had a written respiratory program in place that covered employees cleaning brake and brush housings. NIOSH observed that the safety manager decided whether workers entering the brake and brush housings used respiratory protection. Per the agency’s report, the safety manager’s decision was based on professional judgment following a visual inspection of the amount of dust accumulated in the brush and brake housing. During the agency’s visit, the manager did not require respiratory protection for employees while they cleaned brake dust. Based on NIOSH’s air sampling results, respiratory protection would not be required in this instance. Disposable filtering facepiece N95 respirators were available for voluntary use, but NIOSH staff did not observe employees using them.

NIOSH recommends that the employer evaluate workers’ exposures during brake dust cleaning of the dam’s other two generators. The authors stress that respiratory protection requirements at the dam should be based on both NIOSH’s HHE report (PDF) and subsequent exposure monitoring.