The results of a NIOSH health hazard evaluation of diesel exhaust exposures at three fire stations were discussed. The evaluation was performed in response to a request by the department and local firefighters unit to evaluate potential exposure to diesel exhaust emissions from the fire apparatus. Personal and area air samples were collected on two nights in the kitchens, apparatus bays, dormitories, and other sites in the engine houses when the vehicles' engines were first started and when they began backing into the engine houses upon their return. Samples were not collected on the vehicles when they were away from the firehouses responding to a call. Samples of air outside the engine houses were also collected. The samples were analyzed for elemental carbon (7440440), which was used as a surrogate for particulate diesel exhaust, by a thermal optical method. Personal air elemental carbon exposures measured on the first and second nights varied from 24 to 71 and 14 to 79 micrograms per cubic meter (microg/m3), respectively. The elemental carbon concentrations measured outside of the three engine houses on the two nights averaged 12 and 8.4microg/m3, respectively. Area air elemental carbon concentrations measured in the engine houses on the first and second nights varied from 10 to 823 and 2.2 to 327microg/m3, respectively. The highest exposures were generally measured in the apparatus bays. Significant exposures were measured in the kitchens, dormitories, and other areas away from the apparatus bays. Representative data for an engine house built in 1897 indicated elemental carbon concentrations in the kitchen, dormitory, and television room measured on the first night to be 10, 52, and 34microg/m3, respectively. The author concludes that when diesel powered equipment leaves or returns to an engine house, particulate diesel exhausts are produced inside the apparatus bay. The exhausts can then enter the living quarters. Recommendations for controlling diesel exhaust emissions include installing engine exhaust filters and applying local tailpipe exhaust ventilation and dilution ventilation.