K. Heinze, J. Center, T. Stenersen, C. Dumke FACSM

University of Montana, Missoula, MT

PURPOSE:This study evaluates the relationship between physiological factors and their effects on heat accumulation while wearing a wildland firefighter helmet. METHODS: Eleven male subjects were recruited between the ages of 18-40 with a VO2max between 40-65 ml/kg/min. The trials required the subject to walk at 50% VO2max for 90 min. with an ambient temperature and relative humidity of 35oC and 30% respectively. Prior to exercise, nude bodyweight was obtained, skin and rectal temperature probes were secured, and WLFF personal protective equipment (PPE) (Nomex and standard issue helmet) was donned excluding gloves and a pack. Subjects entered the heat chamber where resting values of heart rate (HR), core temperature (CT), skin temperature on neck and chest (STn, STch), perceived head heat (PHH), skin blood flow on neck and forehead (SBFn, SBFch), and head heat (Tih) were collected. Subjects walked in the heat chamber for two 45 min. increments with a 5 min. rest period in between. Every 15 min. HR, RPE, CT, STn, STch, and PHH were recorded. Subjects received 6 ml/kg of water every 30 min. HR, RPE, CT, STn,STch, PHH and SBFn, SBFchwere recorded at 45 min. and at the end of the trial. Following the trial, nude BW was measured and a urine sample was collected. Pearson correlations determined significant relationships between physiological characteristics and peak outcomes. RESULTS:Body surface area (BSA) related positively with end-trial CT(R=0.78; P=0.013). Increased absolute exercise intensity showed higher STn(R=0.82; P=0.002), SBFn(R=0.68; P=0.020) and sweat rates (R=0.67; P=0.025) during final stages of the trials. Perceived exertion was found to be significantly correlated to PSI (R=0.73; P=0.016). SBFncorrelated positively with Tih(R=0.88; P<0.001), STnand STch(R=0.7; P<0.02). CONCLUSION: This data suggests that larger individuals and greater absolute exercise intensity predispose wildland firefighters to overheating. Non-compensable heat gain from wildland firefighter PPE is related to elevated head heat, ST and SBF suggesting the inability to unload metabolic heat.

Funded by the USFS (14-CR-11138200-009)

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