Presentation Title

The Effect of Vented Helmets on Heat Stress During Wildland Fire-fighter Simulation

Authors' Names

Katherine Christison

Presentation Type

Oral Presentation

Abstract/Artist Statement

Heat related illness is a common issue in wildland firefighters (WLFF) and other occupations due to an inability to maintain thermoregulation over an extended period of time. Heat stress increases during continuous exercise and is magnified by the addition of personal protective equipment (PPE). PPE in the form of shirts, pants, and load carriage loads has been previously shown to result in heat accumulation leading to heat stress. Little research involving the effect of the standard WLFF helmet on heat dissipation exists. While it is understood there is a significant heat accumulation from wearing a helmet, little is known on how helmet vents affect heat stress. PURPOSE: The purpose of this study is to compare heat accumulation in simulated working conditions while wearing standard non-vented WLFF helmets (H) versus a vented helmet (VH). METHODS: In a 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). Following a 10-minute acclimation period, the trial consisted of three intervals of 50 minutes of exercise and 10 minutes of rest. Separated by two weeks, subjects performed the opposing helmet trial. Each trial measured physiological strain index (PSI), skin blood flow at the head and neck (SBFh, SBFn), visual analog scale (VAS), helmet temperature and relative humidity (Th, Rh), rating of perceived exertion (RPE) and heart rate (HR). Data was analyzed using a 2X6 repeated measures ANOVA. RESULTS: All 10 subjects completed both trials. At the end of the 3 hour trial, PSI (6.08±1.45 H, 5.89±1.24 VH), SBFh (238.4±16.8 au H, 225.9±27.6 au VH), SBFn (85.6±8.9 au H, 74.3±10.7 au VH), Th (35.52±0.47°C H, 35.75±0.50°C VH), Rh (45.6±5.1% H, 41.0±5.9% VH), RPE (14.2±1.7 H, 13.3±1.7 VH), and HR (146.8±17.2 bpm H, 144.3±17.9 bpm VH),showed a significant effect of time (p < 0 .05) but were not significant between trials. There were trends towards a significant main effect of trial and interaction on RPE, helmet humidity, and VAS (p≤0.08). SIGNIFICANCE: This study is one of the first to examine the difference between heat accumulation and physiologic stress indices within non-vented WLFF and vented helmets for a duration beyond 90 minutes. While these physiological variables (HR, VAS, PSI, SBFh, SBFn, RPE, Th, and Rh) did not reach trial significance, trends for RPE, helmet humidity, and VAS suggest greater heat dissipation and individual comfort with the vented helmet. This suggests the standard unvented WLFF helmet may contribute to heat gain over time, which may contribute to work output and safety in the field.

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

Mentor Name

Charles Dumke

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Feb 22nd, 10:20 AM Feb 22nd, 10:35 AM

The Effect of Vented Helmets on Heat Stress During Wildland Fire-fighter Simulation

UC 330

Heat related illness is a common issue in wildland firefighters (WLFF) and other occupations due to an inability to maintain thermoregulation over an extended period of time. Heat stress increases during continuous exercise and is magnified by the addition of personal protective equipment (PPE). PPE in the form of shirts, pants, and load carriage loads has been previously shown to result in heat accumulation leading to heat stress. Little research involving the effect of the standard WLFF helmet on heat dissipation exists. While it is understood there is a significant heat accumulation from wearing a helmet, little is known on how helmet vents affect heat stress. PURPOSE: The purpose of this study is to compare heat accumulation in simulated working conditions while wearing standard non-vented WLFF helmets (H) versus a vented helmet (VH). METHODS: In a 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). Following a 10-minute acclimation period, the trial consisted of three intervals of 50 minutes of exercise and 10 minutes of rest. Separated by two weeks, subjects performed the opposing helmet trial. Each trial measured physiological strain index (PSI), skin blood flow at the head and neck (SBFh, SBFn), visual analog scale (VAS), helmet temperature and relative humidity (Th, Rh), rating of perceived exertion (RPE) and heart rate (HR). Data was analyzed using a 2X6 repeated measures ANOVA. RESULTS: All 10 subjects completed both trials. At the end of the 3 hour trial, PSI (6.08±1.45 H, 5.89±1.24 VH), SBFh (238.4±16.8 au H, 225.9±27.6 au VH), SBFn (85.6±8.9 au H, 74.3±10.7 au VH), Th (35.52±0.47°C H, 35.75±0.50°C VH), Rh (45.6±5.1% H, 41.0±5.9% VH), RPE (14.2±1.7 H, 13.3±1.7 VH), and HR (146.8±17.2 bpm H, 144.3±17.9 bpm VH),showed a significant effect of time (p < 0 .05) but were not significant between trials. There were trends towards a significant main effect of trial and interaction on RPE, helmet humidity, and VAS (p≤0.08). SIGNIFICANCE: This study is one of the first to examine the difference between heat accumulation and physiologic stress indices within non-vented WLFF and vented helmets for a duration beyond 90 minutes. While these physiological variables (HR, VAS, PSI, SBFh, SBFn, RPE, Th, and Rh) did not reach trial significance, trends for RPE, helmet humidity, and VAS suggest greater heat dissipation and individual comfort with the vented helmet. This suggests the standard unvented WLFF helmet may contribute to heat gain over time, which may contribute to work output and safety in the field.

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