Physical work limits for Toronto firefighters in warm environments

This study examined the relationship between to reach critical end points (tolerance time [TT] and metabolic rate for three different environmental temperatures (25degreesC, 30degreesC. and 35degreesC. 50% relative humidity), while wearing firefighting protective clothing (FPC) and self-contained breathing apparatus (SCBA). Thirty-seven Toronto firefighters (33 male and 4 female) were divided into four work groups defined as Heavy (H. n = 9), Moderate (M. n = 9), Light (L. n = 10), and Very Light (VL. n = 9). At 25degreesC, 30degreesC, and 35degreesC, TT (min) decreased from 56 to 47 for H.92 to 65 to 54 for M, 134 to 77 to 67 for L, and 196 to 121 for VL. Significant differences in TT were observed across all group comparisons, excluding M versus L at 30degreesC and 35degreesC, and H versus M at 35degreesC. Comparing 25degreesC to 30degreesC, M, L, and VL had significant decreases in TT, whereas only VL had a significant decrease when 30degreesC was compared to 35degreesC. For 25degreesC to 30degreesC, the relative change in TT was significantly greater for L (37%) and VL (41%) compared with H (16%) and M (26%). For 30degreesC to 35degreesC, the relative change among the groups was similar and approximately 17%. During passive recovery at 35degreesC, rectal temperature (T-re) continued to increase 0.5degreesC above T-re (final), whereas heart rate declined significantly. These findings show the differential impact of environmental conditions at various metabolic rates on TT while wearing FPC and SCBA. Furthermore, these findings reveal passive recovery may not be sufficient to reduce T-re below pre-recovery levels when working at higher metabolic rates in hot enviroments.