The effect of a liquid cooling suit on physiological and perceptual strain during uncompensable heat stress when wearing an explosives ordnance disposal suit in hot ambient conditions

  • David Walkland

Student thesis: Master's ThesisMaster of Science by Research


Introduction Explosive ordnance disposal (EOD) operatives often wear protective clothing in the form of an EOD suit for protection when disarming and/or disposal of explosive devices. EOD suits
are heavy, cumbersome and encapsulating, which increases the physical challenge of work and predisposes the wearer to uncompensable heat stress (UHS). If unchecked, UHS will affect physical and cognitive capabilities, limit the amount of work performed, as well as increasing the likelihood of heat strain and/or heat illness, putting the health and safety of the operator at risk.

Aims To characterise the physiological and perpetual benefits of wearing a liquid-cooled suit (LCS) under an EOD suit whist working in high ambient temperatures (40ºC; relative humidity 30%) and to estimate the cooling power provided by the suit.
Methods Seven healthy, non-heat acclimated males (age, 30±5 years old; height, 181±7 cm; body mass, 88.6±11.8 kg) undertook one familiarisation session followed by two experimental trials each separated by at least one week. Trials consisted of walking on a treadmill at 4 km⋅h-1 for 60 mins in
40°C ambient temperatures whilst wearing an EOD suit either with or without an activated waterbased liquid cooling suit (active, AC vs. no cooling, NC respectively) in a balanced cross-over design.
Trials were terminated if the participant's HR exceeds 95% of maximum (220-age) for 1 min or if core temperature reached 39.5ºC or 3ºC greater than initial baseline temperature, whichever was lowest.

Results No participant completed 60 mins of treadmill walking in either condition. However, exercise duration was significantly longer in AC compared to NC (37 mins vs. 32 mins, p<0.05, ηp2 = 0.828). Active cooling resulted in more favourable physiological variables (heart rate, mean skin temperature, core temperature; both gastrointestinal and rectal), and perceptual variables (thermal sensation and comfort). However only gastrointestinal (F (1, 35) = 658,778, p = 0.025, ηp2 = 0.998) and mean skin temperature (F (1, 35) = 513,534, p = 0.028, ηp2 = 0.998) were significantly different in the AC condition compared to NC. Oxygen consumption (V̇ O₂) and rating of perceived exertion
(RPE) did not vary between trials. The cooling power of the LCS for the first 20 mins of the trials (n=7) was estimated as being 73 W from changes in body heat storage between conditions and 199 W
from changes in LCS inlet and outlet water temperatures within AC trials.

Conclusion AC resulted in lower physiological and more favourable perceptual responses when compared with NC. This resulted in a small increase in performance time in AC compared to NC. The cooling power of the LCS system was higher when estimated from changes in water temperature compared to actual cooling transferred to the participants (that estimated from heat storage). Further work investigating the LCS capability at lower work rates, within different environmental conditions and during simulated EOD activities is warranted.
Date of Award2022
Original languageEnglish
Awarding Institution
  • Coventry University
SupervisorDoug Thake (Supervisor)

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