Physiological Strain During Work At Equivalent Wbgt In Wildland Firefighting Garments

Wildland firefighters work in a wide range of environments causing physiological and perceptual strain. PURPOSE: Assess strain when walking on a treadmill wearing wildland firefighter garments in three environments with equivalent wet-bulb globe temperature (WBGT: ~28.5 °C). METHODS: Twelve subjects (age:24 ± 2 y) walked intermittently for 150 min in low-humidity (40 °C, 20% relative humidity (RH)), moderate-humidity (34 °C, 50% RH), and high-humidity conditions (29 °C, 90% RH) wearing fire resistant jacket, pants, gloves, and helmet with only the neck and face exposed. Heart (HR), respiratory (RR), and whole body sweat rates, core temperature (Tc), evaporative heat loss (EHL), and perceptual strain were assessed throughout. RESULTS: At 150 min, Tc (38.5 °C ± 0.3 °C) and HR (167 ± 19 bpm) were lower in low-humidity compared to high-humidity (38.8 °C ± 0.6 °C, p = 0.02; 174 ± 14 bpm, p = 0.004). RR was highest in high-humidity (30.6 ± 10.1 breaths/min, p = 0.002). Thirst, sweating sensation, fatigue, and perceived exertion were lower in low-humidity compared to moderate- and high-humidity (all p < 0.001). The EHL required for heat balance (Ereq) was lowest in high-humidity (p < 0.001) and the EHL deficit (Ereq – EHL) was lower in low-humidity (33 ± 22 W) compared to moderate-humidity (38 ± 23 W, p = 0.002) and high-humidity (39 ± 28 W, p = 0.002). There were no differences in whole body sweat rate (14.8 ± 5.8 g/min, p = 0.58) or thermal sensation (p = 0.40). CONCLUSION: Physiological strain while walking in the heat wearing wildland firefighter garments is higher in a humid environment after 2.5 hours. During shorter intervals, protective garments play a larger role in impaired thermoregulation compared to the environment.