Effects of Helmet Vents on Performance in Simulated WLFF Working Conditions

Heat related illness (HRI) is a vital concern to those working in occupations often conducted in the heat. Personal protective equipment (PPE), required by wildland firefighters (WLFF), aggravates these issues due to uncompensable heat gain. Uncompensable heat gain can result in increased incidence of HRI. Helmets are a standard piece of PPE that WLFF’s must wear from the time they leave the trucks at the beginning of their shift until they are safely back in the vehicles. Previous research has demonstrated that the helmet significantly contributes to heat gain. This may negatively affect physical performance of the WLFF. PURPOSE: The purpose of this study is to determine the impact of the helmet microenvironment on perceived head heat and performance in simulated working conditions while wearing traditional non-vented WLFF helmet (H) compared to a vented helmet (VH). METHODS: In this randomized crossover design, ten male subjects with a VO2max of 59.8 ± 3.6 ml/kg/min walked for two 180-minute trials (at 3.5 mph, 5% grade) in a heat chamber (35○C 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. Each trial measured % dehydration, sweat rate, and work performance (PS, PKJ). Peak helmet temperature, perceived head heat (PVAS), helmet humidity (PHH), heart rate, physiological strain index, rating of perceived exertion, core temperature (PTc), and skin temperature were collected during the performance test. Paired sample t-tests compared differences between the H and VH trials. RESULTS: All 10 subjects were able to finish both trials. Neither sweat rate nor percent dehydration differed between trials. Performance was significantly greater in VH (109.3±8.5 KJ VH vs. 95.9±10.3 KJ H; 703.2 ± 37.5 sec VH vs. 662.7±51.0 sec H ). PHH (45.0±1.3% VH vs. 47.3±1.4% H) and PVAS (91.5±9.9 mm VH vs. 108.8±9.2 mm H) were all significant (p \u3c 0 .05) between trials. A trend in PTc (38.18±0.10○C VH vs 38.32±0.11○C H; p≤0.08) existed. SIGNIFICANCE: This study is one of the first to examine the differences in performance following an extended bout of exercise between non-vented WLFF and vented helmets. These data (PHH, PVAS, PS and PKJ) suggest that a vented helmet could result in an improved helmet microenvironment and greater performance for wildland firefighters. While PTc did not reach significance, a statistical trend suggests that a vented helmet could improve heat dissipation for the body. Thus, the current design of the WLFF helmet may contribute to heat gain, reduced performance, and heat related illnesses for the working WLFF. Supported by the USFS (18-CR-11138100-005