Effect of uncompensable heat from the wildland firefighter helmet

Abstract

Heat accumulation from wearing personal protective equipment can result in the development of heat-related illnesses. This study aimed to investigate factors of heat stress with and without a US standard issue wildland firefighter helmet. Ten male subjects finished a 90-min exercise protocol in a heat chamber (35°C and 30% relative humidity), with standard issue meta-aramid shirt and pants and a cotton t-shirt, and either with or without a wildland firefighter helmet. A randomised crossover design was implemented, with a minimum 2-week washout period. Heart rate, physiologic strain index, perceived head heat, head heat and skin blood flow of the head and neck were measured. At the conclusion of the 90-min trial, heart rate, physiological strain index, core temperature, rating of perceived exertion and perceived head heat showed a main effect of time (P < 0.05). Perceived head heat and head heat exhibited a main effect of trial (P < 0.05). The change in physiologic strain was positively correlated with the change in skin blood flow of the head (r = 0.72, P = 0.02). These data suggest that the current wildland firefighter helmet contributes to heat accumulation. The design of the wildland firefighter helmet lacks ventilation, which, from these data, may result in metabolic alterations and perceived discomfort.

Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Heat Illness: 2024 Update

“…For example, the American football uniform prevents full heat exchange across much of the torso and head and can, therefore, contribute to heat accumulation. 76 A similar effect has been found for other occupational undergarments, 30 helmets, 77 and body armor. 78 Unfortunately, the necessary safety protection provided by some occupational gear results in an elevated risk of heat accumulation—a safety compromise that may be optimized but not eliminated.…”

Effect of vented helmets on heat stress during wildland firefighter simulation

“…The authors understand that current United States Forest Service recommendations restrict the use of vented helmets from approved PPE garments due to certain ANSI requirements. Nonetheless, together with our previous investigation (Gurney et al 2021), we have demonstrated the importance of heat dissipation from the head, which may be ameliorated with the use of a vented helmet.…”

“…To the authors' knowledge, this is the first investigation to establish the effect of an ANSI compliant vented helmet on physiological markers of heat stress during a WLFF simulation, as compared with the current standard WH. Our group has previously established that an unvented helmet results in significant elevations in heat accumulation in those exercising in the heat (Gurney et al 2021). In the current study, significant alterations in PSI, RPE, T HELMET , H HELMET and SBF H were seen during the 180-min trial period, suggesting that WLFF accumulate heat during exercise while wearing standard PPE.…”

“…It was also found that an unvented aerodynamic bicycle helmet resulted in greater head temperature elevation compared with a vented traditional helmet (Lee et al 2013). A previous investigation by our group found the WLFF helmet contributes to heat accumulation, perceived head heat and redirection of blood flow to the head compared with not wearing a helmet (Gurney et al 2021). However, as WLFF are subject to blows to the head, the absence of a helmet is not a consideration in the field (Apuzzo et al 2020).…”