The National Institute for Occupational Safety and Health (NIOSH) conducted a field study at a hydraulic power control components manufacturing plant where n-propyl bromide (nPB) was used as a vapor de greasing solvent. Workers' breathing zone, "in-mask" respirator, and exhaled breath concentrations of nPB and isopropyl bromide (iPB) were measured as were urinary metabolite concentrations of bromide (Br) and propyl mercapturic acid (PMA). n-Propyl bromide has been marketed to replace ozone depleting solvents 1,1,1-trichloroethane and freons, as well as suspect carcinogens trichloroethylene and methylene chloride; chemicals commonly used in industry. Sparse data are currently available to evaluate human exposure to nPB. However, there is concern that nPB may be a hematological, reproductive, or neurological toxin, based on analogy to other Br-propanes, animal studies, and a few case studies. Full-shift exposure to nPB in air samples collected in workers' breathing zones ranged from 0.078 to 2.0 parts per milion (ppm) and from 0.33 to 4.0 ppm in the respirator/breathing zone samples. All of the workers were exposed to nPB at levels below the American Conference of Governmental Industrial Hygienist (ACGIH) Threshold Limit Value of 10 ppm as well as the industrial guideline of 25 ppm published by the EPA in proposed rulemaking. Isopropyl bromide was not detected in air or respirator samples, or was detected in trace quantities. Exhaled breath concentrations of nPB ranged from 0.050 to 0.23 ppm and 0.053 to 0.55 ppm, respectively, for pre- and post-shift samples; iPB was not detected in any of the breath samples. Respirators were used intermittently over 15 to 90 minute periods by assemblers when transferring parts in and out of the vapor degreaser room, and were only used continuously for a few minutes at a time in repetitive intervals ranging from 1 to 25 minutes. The respirator sample remained in the mask when worn around a worker's neck and placed in their breathing zone when respirator use was discontinued. Measured Program Protection Factors (PPF) for each sample pair were calculated by dividing full-shift levels outside the respirator by those measured both inside and outside the respirator. The PPFs ranged from 0.43 to 3.8 for five sample pairs, well below the laboratory "Assigned PF" of 10 for half-mask air purifying respirators. Lower measured PFs may be from face piece leakage, over-loaded cartridges, nPB in exhaled breath, or low respirator use time, which was a significant factor for this operation. Quantitative fit testing also showed two out of the three respirators users failed, attributed to the wrong size respirator or the presence of facial hair. However, two measured PFs were below 0.5, which implies that over-loaded cartridges or nPB in exhaled breath were important factors too. Average urinary Br concentrations measured before the work week began were approximately 65% higher for workers than for unexposed controls who were not employed by this company, but the 24-hour concentrations for workers' were similar to control levels. The 24-hour average PMA concentrations from all workers were over an order of magnitude higher than .the average PMA concentration in controls, suggesting that dermal absorption may contribute to exposure in addition to inhalation. The assembler with the lowest breathing zone concentration of nPB had urinary metabolite levels similar to those measured in controls. Recommendations include substitution of nPB solvents with a less toxic solvent, periodic exposure monitoring, impermeable gloves to nPB, ventilation modifications, respiratory protection program improvements, and routine medical examinations.
National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluations and Field Studies, Industrywide Studies Branch, 4676 Columbia Parkway, Cincinnati, OH 45226