The Influence of Arc-Flash and Fire-Resistant Clothing on Thermoregulation during Exercise in the Heat

Abstract

We evaluated the effect of arc-flash and fire-resistant (AFR) clothing ensembles (CE) on whole-body heat dissipation during work in the heat. On 10 occasions, 7 males performed four 15-min cycling bouts at a fixed rate of metabolic heat production (400 W) in the heat (35°C), each separated by 15-min of recovery. Whole-body heat loss and metabolic heat production were measured by direct and indirect calorimetry, respectively. Body heat storage was calculated as the temporal summation of heat production and heat loss. Responses were compared in a semi-nude state and while wearing two CE styles: (1) single-piece (coveralls) and (2) two-piece (workpant + long-sleeve shirt). For group 1, there was one non-AFR single-piece CE (CE1_STD) and three single-piece CE with AFR properties (CE2_AFR, CE3_AFR, CE4_AFR). For group 2, there was one non-AFR two-piece CE (CE5_STD) and four two-piece CE with AFR properties (CE6_AFR, CE7_AFR, CE8_AFR, CE9_AFR). The workpants for CE6_AFR were not AFR-rated, while a cotton undershirt was also worn for conditions CE8_AFR and CE9_AFR and for all single-piece CE. Heat storage for all conditions (CE1_STD: 328 ± 55, CE2_AFR: 335 ± 87, CE3_AFR: 309 ± 95, CE4_AFR: 403 ± 104, CE5_STD: 253 ± 78, CE6_AFR: 268 ± 89, CE7_AFR: 302 ± 70, CE8_AFR: 360 ± 36, CE9_AFR: 381 ± 99 kJ) was greater than the semi-nude state (160 ± 124 kJ) (all p ≤ 0.05). No differences were measured between single-piece uniforms (p = 0.273). Among the two-piece uniforms, heat storage was greater for CE8_AFR and CE9_AFR relative to CE5_STD and CE6_AFR (all p ≤ 0.05), but not CE7_AFR (both p > 0.05). Differences between clothing styles were measured such that greater heat storage was observed in both CE1_STD and CE2-4_AFR relative to CE5_STD. Further, heat storage was greater in CE2_AFR and CE4_AFR relative to CE6_AFR, while it was greater in CE4_AFR compared to CE7_AFR. Body heat storage during work in the heat was not influenced by the use of AFR fabrics in the single- or two-piece uniforms albeit less heat was stored in the two-piece uniforms when no undershirt was worn. However, heat storage was comparable between clothing styles when an undershirt was worn with the two-piece uniform.

Keywords:

• body heat storage
• calorimetry
• heat stress
• personal protective clothing
• whole-body heat loss