Active Versus Passive Cooling During Work in Warm Environments While Wearing Firefighting Protective Clothing

Abstract

This study examined whether active or passive cooling during intermittent work reduced the heat strain associated with wearing firefighting protective clothing (FPC) and selfcontained breathing apparatus (SCBA) in the heat (35°C, 50% relative humidity). Fifteen male Toronto firefighters participated in the heat-stress trials. Subjects walked at 4.5 km·h⁻¹ with 0% elevation on an intermittent work (50 min) and rest (30 min) schedule. Work continued until rectal temperature (T _re ) reached 39.5°C, or heart rate (HR) reached 95% of maximum or exhaustion. One of three cooling strategies, forearm submersion (FS), mister (M), and passive cooling (PC) were employed during the rest phases. Tolerance time (TT) and total work time (WT) (min) were significantly increased during FS (178.7 ± 13.0 and 124.7 ± 7.94, respectively) and M (139.1 ± 8.28 and 95.1 ± 4.96, respectively), compared with PC (108.0 ± 3.59 and 78.0 ± 3.59). Furthermore, TT and WT were significantly greater in FS compared with M. Rates of T _re increase, HR and were significantly lower during active compared with passive cooling. In addition, HR and T _re values in FS were significantly lower compared with M after the first rest phase. During the first rest phase, T _re dropped significantly during FS (∼0.4°C) compared with M (∼0.08°C) while PC increased (∼0.2°C). By the end of the second rest period T _re was 0.9°C lower in FS compared with M. The current findings suggest that there is a definite advantage when utilizing forearm submersion compared with other methods of active or passive cooling while wearing FPC and SCBA in the heat.

Keywords:

• cooling strategies
• exercise tolerance
• metabolic rate
• protective clothing
• rectal temperature
• uncompensable heat stress

ACKNOWLEDGMENTS

The authors wish to acknowledge the assistance and technical support of Jan Pope, Robert Limmer, John Hilton, and Peter Tikuisis. As well, a special thanks to all of the volunteers from the Toronto Fire Services for their willingness to participate in this research.

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

Notes

^A F < M and PC.

^B M < PC.

^A F > M and PC.

^B M > PC.

^A All comparisons significantly different.