AbstractWe undertook a study to determine the acute effects of routine firefighting on lung function and the relationship between these acute effects and nonspecific airway responsiveness. For 29 firefighters from a single fire station, we calculated the concentration of methacholine aerosol that caused a 100% increase in specific airway resistance (Pc100). Over an 8‐week period we then measured FEV1 and FVC in each firefighter before and after each 24‐hr workshift and after every fire. From 199 individual work‐shifts without fires, we calculated the mean ± 2 SD across‐workshift change in FEV1 and FVC for each firefighter. Eighteen of 76 measurements obtained within 2 hr after a fire (24%) showed a greater than 2 SD fall in FEV1 and/or FVC compared to two of 199 obtained after routine workshifts without fires (1%; p<.001). On 13 of 18 occasions when spirometry decreased significantly, we obtained repeat spirometry (post‐shift) 3–18.5 hr after fires, and on four of these occasions FEV1 and/or FVC were still more than 2 SD below baseline. Decrements in spirometry occurred as often in firefighters with high Pc100s as in those with low Pc100s. In two firefighters in whom FEV1 and FVC fell by more than 10% after fires, we repeated measurements of methacholine sensitivity, and it was increased over the prestudy baseline. These findings suggest that routine firefighting is associated with a high incidence of acute decrements in lung function. The persistence of these decrements, the lack of association with baseline airway responsiveness, and the association with acute increases in airway responsiveness all suggest that these decrements in lung function are not due merely to irritant broncho
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