The effect of heat acclimation on thermal strain during Explosives Ordnance Disposal (EOD) related activity in moderate and hot conditions. C. D. Thake 1 , M. J. Zurawlew 1 , M. J. Price 1 and M. Oldroyd 2 1 Faculty of Health and Life Sciences, Coventry University, Priory Street, Coventry, CV1 5FB 2 NP Aerospace, Foleshill Road, Coventry, CV6 5AQ Contact person: d.thake@coventry.ac.uk INTRODUCTION Uncompensable heat stress (UHS) occurs when the rate of evaporation required from the body’s surface to maintain thermal equilibrium exceeds the evaporative capacity of the environment (Cheung et al., 2000). The resultant thermal strain is associated with reduced physical and cognitive performance and comfort as well as deterioration of job specific tasks (Taylor and Orlansky, 1993). UHS can occur when wearing a range of protective equipment and is determined by, amongst other factors, body surface coverage, characteristics of the garment (thermal insulation and evaporative resistance), metabolic rate and ambient conditions (Hanson, 1999). The rate of onset of thermal strain can be reduced by increasing the capacity for heat storage (e.g. pre-cooling; Marino, 2002 and increasing fitness; Selkirk and McLellan, 2001) or by reducing the rate of heat storage (e.g. cooling systems; Thake and Price, 2007 and altering work to rest ratios; McLellan et al., 1993). Heat acclimation is a further method commonly used to reduce thermal strain and its use has been investigated in various modes of personal protective equipment (PPE; for review see Cheung et al., 2000). However the modes PPE that have been examined weigh substantially less than an explosives ordnance disposal (EOD) suit and usually fully encapsulate the wearer, unlike the partial coverage of the EOD suit. Furthermore the effect of acclimation is usually only investigated at hot ambient temperatures. Therefore the aim of this study was to evaluate the impact of acclimation on physiological and perceptual strain during activities representative of EOD operations, with and without wearing an EOD suit, in moderate (20°) compared to hot (40°C) conditions. METHODS With local ethical committee approval six non heat acclimated participants (5 male and 1 female; age 22±3 yrs; body mass 79.5±12.1 kg; stature 176.2±5.3 cm) were recruited. Four experimental visits took place prior to 6 acclimation sessions (PRE) and were repeated thereafter (POST) to enable a pre to post acclimation comparison to be made between each condition. Acclimation consisted of six one hour treadmill walks (4 km hr -1 whilst wearing a 37 kg large EOD suit (Ergotec 4010, NP Aerospace, UK) with the duel integral fans turned off in 22±1 C; 47±5% relative humidity (RH). These six sessions were completed over 9 days in a 2 day on 1 day off pattern. Pre and post acclimation trials were conducted over an eight day period and consisted of temperate (20 C) and hot (40 C) conditions whilst wearing the same EOD suit with the fan system turned on (delivering 200 and 100 L min -1 of ambient air to the wearers back and head