Making chemical & biological protective gloves vapour permeable reduces thermoregulatory strain better than making armour, respirator or overboots permeable

Introduction

Wearing chemical and biological (CB) protective equipment causes thermoregulatory strain by restricting evaporative cooling. We identified [1] that a moisture vapour impermeable (MVIP) body armour liner (BAL) imposed a greater thermal burden than MVIP CB gloves (G), overboots (O) or respirator (R). The previous study progressively and cumulatively removed these MVIP items across 5 conditions when wearing a CB protective suit. This study is a repeat, except that items were removed in isolation and replaced for subsequent conditions to maintain a more uniform thermal load across comparisons. The aims of this study were to quantify the thermal burden imposed by each MVIP item whilst maintaining a high thermal load between conditions to identify the potential benefits if future equipment was made moisture vapour permeable (MVP). A second aim was to determine whether the previous experimental design [1] influenced the thermal burden imposed by each MVIP item. We hypothesised that removal of a MVIP item would reduce heat strain in this order BAL>G>R>O.

Methods

Following a favourable ethical opinion, 13 males volunteered for this five-condition, repeated measures study, stepping at a light intensity VO₂ 13.6 mL.kg^-1.min^-1), interspersed with 20-minute rest periods in a hot and dry environment (40.5 °C and 20% relative humidity) for a maximum of 170 minutes; the last hour being continuous work. Conditions varied in which combinations of MVIP items were worn with a CB suit. In Control (CON) all items were worn, in subsequent conditions, only one item was removed: N_R (no R), N_BAL (no BAL), N_G (no G) and N_OB (no O). When removed the mass of the item was substituted at the same body site thereby simulating that item 100% MVP but without reducing the metabolic cost of wearing the item.

Results

Removing G reduced thermoregulatory strain most, as 7 participants completed the full 60 min of stepping in the final work period compared to 1 (CON), 2 (N_OB), 5 (N_R) and 5 (N_BAL). Removing G attenuated the rate of increase in rectal temperature (T_re) during the final work period compared to CON by 0.37°C.hr^-1 (p < 0.001) resulting in a 6% extension to stepping time during the final work period (p < 0.05). Predicted tolerance time (TT) to a T_re of 40°C (participants stopped when T_re = 39°C) was extended by 13.3% (p < 0.01). In N_G, the rate of cooling was augmented in the final rest period with the final change in T_re lowered by 0.14°C (p < 0.01). The rise in mean body temperature was attenuated from 90 minutes with the greatest attenuation being 0.24°C (p < 0.0001) in N_G. During N_G the physiological strain index (PSI) was reduced by 12.7% (p < 0.001). Removing G also reduced RPE during Rest 2 (p < 0.05), final work (p < 0.001) and final rest (p < 0.0001) and improved ratings of thermal comfort during final work (p < 0.01) and rest (p < 0.001). Removing BAL increased sweat evaporation by 10.2%, yet did not extended TT. Removing R improved the PSI by 15.7% (p < 0.05) but did not improve TT. Removing O did little to reduce thermoregulatory strain.

Conclusion

With the thermal load maintained across conditions, removal of any of the MVIP items reduced the thermal burden with removing G causing the greatest reduction to thermoregulatory strain. This is in contrast to [1] where BAL afforded the biggest benefit when removed. This method rather than [1] offers a better assessment of the contributing burden of protective equipment in human studies. We partly accept our hypothesis; thermal strain was reduced most by removing G, not BAL.