Thermal response during explosive ordnance disposal operations

: optimising the use of phase change material vests in hot conditions

Abstract

Purpose: The aim of this study was to evaluate the thermal physiological and perceptual influence of replacing a torso covering phase change cooling material (PCM)under aMk6a Explosive Ordnance Device (EOD)suit after one hour of EOD activity representative of that undertaken during explosive ordinance disposal activity in hot environments (40°C).

Method: Following ethical approval from the Coventry University Ethics committee six non heat acclimated male volunteers (age 22±3 yrs; body mass 78.1±9.3 kg; stature 176.3±6.5 cm) participated in this investigation. Three trials were conducted by each participant at an ambient temperature of 40°C whilst wearing a 38 kg EOD suit (Mk6, NP Aerospace, UK). The protocol was comprised of three16 minute30 second activity cycles; 10 minute rest (helmet, shield, jacket and PCM vest, if worn, were removed and donned in first and last 90 seconds respectively); three16 minute30 second activity cycles (a total of 109 min) that took place within a 3 m × 5 m enclosed area. Each activity cycle consisted of treadmill walking, manual activity, crawling and searching, arm ergometry and seated rest. In a randomised cover-over type design participants did not wear PCM (NoPCM); wore one PCM vest throughout (PCM1) or changed the PCM vest in the 10 minute rest period (PCM2). The PCM vests used, phase changed at 25°C and were worn over a cotton t-shirt. Data was analysed using a general linear model analysis of variance (ANOVA). Significant (P<0.05) main effects for condition, time and condition × time interaction were investigated using Tukey post hoc tests.

Results: In all three conditions thermal physiological strain increased with activity duration and was greatest following a ten minute break (P<0.001, main effect for time for all variables). During the first three activity cycles responses were greatest in PCM conditions and tend to be similar within PCM1 and PCM2 conditions. Perceived rate of exertion(RPE), thermal sensation and thermal comfort followed this same trend (p<0.001, Main effect for time). Observations during the ten minute rest period (49:30-59:30,min:sec) identified that the PCM during PCM1 and PCM2 trials had completely melted during the first 3 activity cycles. Physiological strain indices (PhSI) was reduced during the rest period (49:30-59:30,min:sec) by 1.2±0.6 across all three conditions. During the final 3 activity cycles heat storage(S)increased at the greatest rate within PCM1 trials and at the lowest rate with PCM2 trials (p<0.001). No significant difference was identified between NoPCM and PCM1 trials post break (NS for core temperature (T_c), mean skin temperature(T_msk),and heart rate(HR)) with significantly reduced strain within PCM2 trials (p<0.01 for HR and p<0.001 for T_c and T_msk in comparison to NoPCM and PCM1).Perceptual strain indices(PeSI)and perceptual data was lowest post break within PCM2 trials in comparison to NoPCM and PCM1 (P<0.001). Overall sweat production for trials reflected the physiological response with greatest level of sweat identified in NoPCM and least in PCM2 trials.
Conclusion: Wearing a PCM vest during the simulated EOD activity for 50 minutes had no significant impact on heat strain despite the PCM completely melting during this period. Heat strain was reduced during a second 50 minute bout of EOD activity when a new PCM vest was worn, but not when the melted vest from the first work period was re-applied. Following 50 minutes of EOD activity in 40°C no significant increases were identified in T_re or T_gi. Irrespective of a PCM being worn HR, T_msk and S all increased to the same level. Following a second 50 minutes of EOD activity, rectal temperature (T_re) and gastro-intestinal temperature (T_gi) increased significantly with T_msk, HR and S continuing to rise. No indicators of heat strain (T_re, T_msk, T_gi, HR, S or PhSI) was reduced in PCM1 trials compared to control however all were significantly lower when a new charged vest was worn (PCM2).  

Date of Award	Oct 2011
Original language	English
Awarding Institution	Coventry University
Supervisor	Doug Thake (Supervisor)