Ice Vests Extend Physiological Work Time While Wearing Explosive Ordnance Disposal Protective Clothing in Hot Conditions
Introduction: Explosive ordnance disposal (EOD) technicians may be required to work in hot environments while wearing heavy protective clothing. The uncompensable heat stress experienced limits their work time in such conditions. We investigated the ability of an ice vest to attenuate physiological strain and subsequently extend work tolerance.
Method: Eight male participants (24.3±4.1 yr, 51.9±4.6 mL∙kg-1∙min-1) walked (4.5 km·h-1) on a treadmill in an environmental chamber (35 °C; 50% relative humidity). Participants wore either an EOD suit (EOD; Med-Eng EOD 9; 33.4kg) or EOD and ice vest (EOD+IV; ICEEPAK Australia; 34.6kg). Heart rate, rectal and skin temperature were recorded continuously. Trials were terminated due to: rectal temperature 39 °C; 60 minutes walking duration; heart rate 90% of maximum; volitional fatigue. Order of trials was randomised across participants, separated by at least seven days and commenced at the same time of the day.
Results: The majority of trials (15/16) were terminated based on heart rate criteria. Participants walked longer in EOD+IV compared to EOD (8.1±7.4 min, p<0.05). EOD+IV resulted in cooled skin and subsequently whole body temperatures (p<0.001). An interaction between condition and time was identified for heart ratewith EOD+IV becoming significantly lower after 30 minutes of exercise (p<0.001).
Conclusions: Work time improved by 21% in EOD+IV. The participant’s heart rate, skin and whole body temperature were lower while wearing the ice vest. With heat dissipation via the periphery facilitated by the EOD+IV, the observed reductions in heart rate may reflect the preservation of central blood volume enabling the heart to maintain cardiac output. Thus, the cardiovascular inefficiency that limited performance time in the EOD condition was attenuated. Overall, the results highlight the benefit of an inexpensive cooling device in assisting EOD technicians working in a hot environment.