Impact of a Flame Resistant Synthetic Material Base Layer on Heat Stress Factors

Protective clothing worn by wildland firefighters (WLFF) may increase physiological strain and heat stress factors due to increased insulation and decreased ventilation. PURPOSE: To examine the effects of a flame resistant synthetic material base layer on heat stress. METHODS: Ten recreationally active males completed two trials of intermittent (50-min walking, 10-min sitting) treadmill walking (2.5mph, 4% grade) over 3 hours in a hot, dry environment (35⁰C, 30% rh). Participants wore standard WLFF Nomex pants, shirt with either a cotton base layer (C) or a flame resistant synthetic base layer (S), while carrying a 35lb pack, hard hat, and gloves. Core (Tc) and skin (Tsk) temperature was measured continuously throughout the trial. Skin blood flow (SBF) and skin temperature (DTsk) was recorded via laser doppler throughout the exercise. Statistical analyses were performed using SPSS 22.0. 2X4 repeated measures ANOVA were used for Tc and Tsk. 2X5 repeated measures ANOVA were used for SBF and DTsk. RESULTS: Significant main effects for time were found on Tc (p=0.000) and Tsk (p=0.003). No significant trialXtime interactions were found in Tc (p=0.077) and Tsk (p=0.086). SBF showed significant main effects for time (p=0.001) and trialXtime interaction (p=0.001). Significant main effects for time were found on DTsk (p=0.001). Comparisons for SBF and DTsk were made between peaks, nadirs, and the three post-exercise periods for C and S. Significant main effects for time were found on SBF peaks (p=0.001), nadirs (p=0.028), and posts (p=0.001). Significant main effects for time were found on DTsk peaks= (p=0.019) and posts (0.001). CONCLUSION: Although not significant, trends were seen that suggest the flame resistant synthetic material base layer may increase physiological strain and heat stress factors