Physical Work Limits for Toronto Firefighters in Warm Environments

Abstract

This study examined the relationship between time to reach critical end points (tolerance time [TT] and metabolic rate for three different environmental temperatures (25°C, 30°C, and 35°C, 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 25°C, 30°C, and 35°C, TT (min) decreased from 56 to 47 to 41 for H, 92 to 65 to 54 for M, 134 to 77 to 67 for L, and 196 to 121 to 87 for VL. Significant differences in TT were observed across all group comparisons, excluding M versus L at 30°C and 35°C, and H versus M at 35°C. Comparing 25°C to 30°C, M, L, and VL had significant decreases in TT, whereas only VL had a significant decrease when 30°C was compared to 35°C. For 25°C to 30°C, the relative change in TT was significantly greater for L (37%) and VL (41%) compared with H (16%) and M (26%). For 30°C to 35°C, the relative change among the groups was similar and approximately 17%. During passive recovery at 35°C, rectal temperature (T_re) continued to increase 0.5°C 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 environments.

Keywords:

• metabolic rate
• protective clothing
• rectal temperature
• uncompensable heat stress
• work tolerance

ACKNOWLEDGMENTS

The authors acknowledge the assistance and technical support of Jan Pope, Robert Limmer, John Hilton, and Peter Tikuisis. Also, special thanks to all of the volunteers from the Toronto Fire Services for their willingness to participate in this research supported by the Ontario Workplace Safety Insurance Board.

Funding for this study was provided by the Ontario Workplace Safety Insurance Board.

Notes

^A A_D = surface area.

^B HR_peak = peak heart rate.

^C ṾO_2peak = peak aerobic power.

^D BF = body fatness.

AWithin significance: H-30°C > H-25°C and H-35°C.

BBetween significance: H < M.

CWithin significance: M-25°C < M-30°C and M-35°C.

DBetween significance: M > H, L, and VL.

EWithin significance: L-30°C > L-35°C.

FBetween significance: L > H.

GBetween significance: VL > H.

HBetween significance: VL < M and L.

IWithin significance: VL-25°C < VL-30°C and VL-35°C.

^A H < M, L, VL.

^B H < L, VL.

^C M < L, VL.

^D M < VL.

^E L < VL.