2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
EMPIRICALLY-BASED WET-BULB-GLOBE TEMPERATURE LIMITS
FOR USE IN MALE, BRITISH SOLDIERS, NOT ACCLIMATISED TO
HEAT
A.S. Weller and W.R. Withey
QinetiQ, Air Division - HPPE, Farnborough, GU14 0LX, UK
Contact person: asweller@QinetiQ.com
INTRODUCTION
Heat illness is a routine and significant risk in military personnel of many nations. In the
British Armed forces, this risk is managed, in part, by defining wet-bulb-globe temperature
(WBGT) limits for different in-Service work categories (‘Low’, ‘Medium’, ‘High’, ‘Very
high’ and ‘Extreme’) (JSP 539, 2003). However, these limits have not been validated in the
user population and therefore carry unknown heat illness risk. To test anecdotal reports and
heat strain predictions that the WBGT limits are overly cautious, a research programme was
undertaken to provide empirically-based WBGT limits in male soldiers, not acclimatised to
heat. Initial studies quantified the intra- and inter-individual variability in heat strain and
established that the population-based deep-body (rectal) temperature (Tre) should be limited to
38.2 °C (Weller and Withey, 2004; 2005). The aim of the present study was to propose
suitable WBGT limits based on this Tre threshold.
METHODS
The study, which was approved by the QinetiQ Ethics Committee, was divided into two
phases (A and B). In Phase-A, 12 male soldiers representative of British Armed Forces
personnel (age, 23.1 (1 SD, 4.6) y; body mass, 80.1 (12.2) kg; aerobic power, 53.0 (5.9)
ml·min -1 ·kg -1 ), undertook five Heat Tests (HT) - HT1a, HT2a, HT3a, HT4a and HT5,
consisting of treadmill exercise in a hot chamber. The target metabolic rates (achieved by
alterations in treadmill speed and/or incline) were 175, 325, 500, 658 and 821 watts for
HT1a–HT5, respectively, and were consistent with the in-Service work categories (see
above). The thermal environments were controlled at the WBGT limits predicted by
mathematical modelling (38, 32, 25, 20 and 20 °C, for HT1a–HT5, respectively), with blackglobe
temperature equal to dry-bulb temperature, relative humidity (rh) maintained between
20 and 27 %, and air speed (Va) kept to a minimum (< 0.2 m·s -1 ). Subjects wore lightweight
combat clothing and boots during the walking Heat Tests (HT1a–HT4a), and shorts, a T-shirt
and sports shoes during the running Heat Test (HT5). Heat strain variables were measured
throughout the Heat Tests, and the WBGT limits were categorised as either: ‘Conservative’
(Tre < 38.0 °C), ‘Satisfactory’ (Tre = 38.0–38.4 °C), or ‘Risky’ (Tre > 38.4 °C). Although the
WBGT limits evaluated were relevant for 60- (HT1a–HT4a) and 30-minute (HT5) exposures,
the Heat Tests were scheduled to last 120- and 45-minutes, respectively, to establish any
subsequent rise in Tre. An increase in Tre of greater than 0.5 °C between 60 and 120 minutes
was considered unacceptable.
RESULTS
HT1a was considered ‘Risky’, and the measured work rate during HT2a exceeded the target
work rate by 20%, whereas HT3a, HT4a (120 minutes) and HT5 (45 minutes) were
categorised ‘Satisfactory’. Tre during the Heat Tests in Phase-A are shown in Figure 1.
500