Health Hazard Evaluation Report, HETA-2000-0309-2857, Lehigh Portland Cement Company, Union Bridges, Maryland.
On May 30, 2000, the National Institute for Occupational Safety and Health (NIOSH) received a health hazard evaluation (HHE) request from the Paper, Allied Industrial, Chemical, and Energy Workers Union Local 2-0031 regarding fly ash exposures during the cement manufacturing process at the Lehigh Portland Cement Company in Union Bridge, Maryland. The union was concerned about possible exposures to crystalline silica as a constituent of the fly ash (approximately 1-6%) used in the cement manufacturing process. On July 24-25, 2000, NIOSH investigators conducted a site visit at the Lehigh Portland Cement Company. Area and personal breathing zone (PBZ) air samples were collected for total dust, respirable dust, and crystalline silica. Bulk samples of the fly ash and raw feed were also collected and analyzed for crystalline silica content and elements (e.g., chromium, copper, nickel, lead, magnesium, manganese, titanium, zinc, etc.). A return site visit was conducted on December 13, 2000, to collect PBZ air samples for elements. PBZ air samples collected for respirable dust, quartz (crystalline silica), cristobalite, and elements did not indicate any exposures exceeding applicable exposure criteria. Three area samples collected at different times in the raw mill separator area indicated total dust concentrations of 149 milligrams of dust per cubic meter of air (mg/m3), 14 mg/m3, and 20 mg/m3. (The settled dust [on equipment, stairs, floors, etc.] in the raw mill area, and leaks in the process equipment may affect dust sample concentrations collected at different times during the day). Three out of seven workers sampled during the initial site visit had total dust time-weighted average (TWA) exposures above the American Conference of Governmental Industrial Hygienists' (ACGIH) Threshold Limit Value (TLV) and Mine Safety and Health Administration (MSHA) permissible exposure limit (PEL) of 10 mg/m3. Two of these workers were performing work tasks in the mill room and had TWA exposures that also exceeded the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) for total dust (15 mg/m3). PBZ air samples collected on a worker repairing a leak in the process equipment (located within the raw mill building) indicated an extremely high total dust TWA concentration (3800 mg/m3). This sample was not representative of the worker's breathing zone exposure (dust was blowing directly on the sampling cassette at a high velocity while he was repairing the leak). However, because of the high concentration in this sample, it is possible that the worker's true exposure to total dust concentrations was well over applicable exposure criteria. All area and PBZ air samples for quartz (crystalline silica) were below applicable exposure criteria. However, PBZ air samples indicated that total dust TWA exposures were in excess of applicable exposure criteria. Recommendations to control total dust exposures include shutting off process equipment when performing maintenance activities to repair leaks; fixing leaks in process equipment to reduce dust generating sources; using engineering and administrative controls when feasible; using respirators when other controls are not feasible; using vacuums (with P95 filters) instead of pressurized air to clean off work clothing; and re-sampling after any process changes to evaluate worker exposures under new conditions.