K. Christison, S. Gurney, C. Dumke, FACSM

University of Montana, Missoula, MT

Personal protective equipment (PPE), required by wildland firefighters (WLFF), aggravates heat related illnessdue to uncompensable heat gain. PURPOSE: To identify physiologic measures resulting in improved performance due to wearing a vented helmet (VH) compared to a traditional non-vented WLFF helmet (H) in simulated working conditions. METHODS: In this randomized crossover design, ten male subjects with a VO2maxof 59.8 ± 3.6 ml/kg/min walked for two 180-minute trials (at 3.5 mph, 5% grade) in a heat chamber (35C and 30% relative humidity). Trials started with a nude body weight measurement following urine collection, then a 10-minute chamber acclimation period in full WLFF gear. The trials involved three intervals of 50 minutes of exercise and 10 minutes of rest, followed by a performance test to exhaustion. A post trial nude body weight and urine sample were also collected. Subjects were provided with 5 ml of water/kg of body weight every 30 minutes. Separated by a two-week washout, subjects repeated the trial with the other helmet. RESULTS: A higher relative intensity increased Physiologic Strain Index (PSI) (R=0.63, P=0.049), while an increased PSI at the end of the 170-minute trial led to a decrease in performance (KJ) (R= -0.78, P=0.007). End-trial heart rate was negatively correlated with work achieved during the performance test (R= -0.91, P<0.001). Rating of perceived exertion (RPE) was positively correlated with skin blood flow at the head (SBFh) (R=0.66, P=0.002) and helmet humidity (HH) (R=0.67, P=0.001). In the H trial, core temperature and HHwere positively correlated (R=0.67, P=0.035). CONCLUSION: These data suggest that the redistribution of blood-flow to the head and the helmet’s microenvironment resulted in an increased level of perceived exertion. The relative intensity that individuals performed the 170-minute trial affected their physiological strain, and an increase in that strain during the trial inhibited their ability to perform work during the performance test. Together, the uncompensable heat gain from work completed with a WLFF helmet could negatively affect performance and perhaps safety in the field.

Supported by the USFS (18-CR-11138100-005).

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