In response to a request from the US Department of the Interior, National Park Service, an investigation was begun into possible hazardous exposures for workers fighting the Arch Rock Fire (SIC- 0851) in Yosemite National Park, California. The survey assessed exposure to carbon-monoxide (630080) (CO), sulfur-dioxide (7446095) (SO2), nitrogen-dioxide (10102440), respirable particulate matter, polynuclear aromatic hydrocarbons, volatile organic compounds, aldehydes, and acid gases. Samples of new and washed bandannas, often used for respiratory protection by firefighters, were also measured to determine the pore size. Cross shift changes in lung function, CO levels in exhaled breath, and respiratory and central nervous system symptoms were monitored. The study determined that there was a hazard at the operation, with three CO exposure concentrations being above the adjusted guideline of 21 parts per million (ppm) and two of the 11 exposure concentrations for SO2 being above the NIOSH recommended exposure limit of 2.0ppm. Evidence was also gathered which suggested that there were acute changes in lung function associated with the activities of Type-I crew members. The authors conclude that a potential health hazard existed from exposure to carbon-monoxide and sulfur dioxide. The authors recommend that respiratory protection and respiratory surveillance programs be instituted.