Abstract
ObjectiveThe use of personal cooling systems to mitigate heat strain on first-responders achieves two potential performance benefits relative to the absence of such cooling: (1) the completion of a workload with less effort; and/or (2) the completion of a greater workload for the same effort. Currently, claims made by manufacturers regarding the capability of their products for use in conjunction with chemical/biological protective clothing remain largely unsubstantiated. The purpose of this investigation was to evaluate the means by which heat strain can be alleviated during uncompensable heat stress in chemical/biological clothing, using the ASTM F2300-10 methodology.MethodsEight healthy males completed five trials of continuous walking (4.5 km h−1; 35°C; 49% RH) for up to 120 min while wearing one of four cooling systems and/or a National Fire and Protection Association 1994 Class-3 chemical/biological ensemble. The four cooling methods (ice vest [IV], phase-change vest [PCM], water-perfused suit [WS], and combination ice slurry/ice vest [SLIV]) and no cooling (CON).ResultsWe observed significant improvements in trial times for IV (18 ± 10 min), PCM (20 ± 10 min) and SLIV (22 ± 10 min), but no differences for WS (4 ± 7 min). Heart rate, rectal, mean skin, and body temperatures were significantly lower in all cooling conditions relative to control at various matched time points in the first 60 min of exercise. Thermal sensation, comfort and perceived exertion all had significant main effects for condition, and time, there were no differences in their respective interactions.ConclusionThe IV, PCM, and SLIV produced lower heart rate, mean skin, rectal and mean body temperatures in addition to improved work times compared to control. The WS did not improve work times possibly as a result of the cooling capacity of the suit abating, and magnifying thermal insulation. Considering the added time and resources required to implement combination cooling in the form of ice slurry and ice vest (SLIV), there was no significant additive effect for perception, cardiovascular strain, rectal temperature and total trial time relative to the phase change vest or ice vest alone. This may be a product of a “ceiling” effect for work limit set to 120 min as part of ASTM F2300-10.
Highlights
Moderate to high-intensity work in the presence of environmental heat stress forces simultaneous demands upon the cardiovascular system by increasing the need for blood flow for thermoregulation and at the active musculature (Kenney et al, 2014)
Claims made by manufacturers of personal cooling systems regarding the capability of their products for use in conjunction with chemical/biological protective clothing context remain largely unsubstantiated
Considering the added time and resources required to implement combination cooling in the form of ice slurry and ice vest (SLIV), there was no significant additive effect for perception, cardiovascular strain, TR and total trial time relative to the phase change vest or ice vest alone in work bouts less than 120 min
Summary
Moderate to high-intensity work in the presence of environmental heat stress forces simultaneous demands upon the cardiovascular system by increasing the need for blood flow for thermoregulation and at the active musculature (Kenney et al, 2014). The physiological strain imposed on the individual can be compounded further if workloads are prolonged and heat loss mechanisms are blunted (e.g., encapsulating protective clothing and/or confined spaces) (McLellan et al, 2013; Morrison et al, 2014). Such scenarios can lead to a state of uncompensable heat stress, and if ignored will manifest as signs and symptoms of exertional related heat illness or injury (e.g., heat cramp, heat syncope, and heat stroke) (Bouchama and Knochel, 2002; Casa et al, 2015). The procedure of worker cooling can be divided into three key components, (1) Timing: cooling before, during and/or following work bouts; (2) Application: internal (e.g., ingestion/inhalation) or external cooling (e.g., heat loss at the skin); and (3) Means: passive cooling (exothermic, e.g., absorb body heat and dissipate it into the environment such as an evaporative cooling vest; and/or heat absorbing, utilizing body heat to generate an endothermic reaction such as an ice vest) or active cooling (e.g., uses a power source to circulate a cooling medium, liquid or gas, across the body)
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