2007, Piran, Slovenia

Clothing
REDUCTION OF HEAT STRESS IN AN IMPERMEABLE
CHEMICAL-BIOLOGICAL PROTECTIVE SUIT BY WETTING
THE OUTSIDE SURFACE
1 Weyl C.L., 1 Farnworth B., 2 Lusina S.-J.C., 2 Cirillo M., 2 Wong C., 2 White M.D.
1 W.L. Gore & Associates, Inc.
2 Laboratory for Exercise and Environmental Physiology,
School of Kinesiology, Simon Fraser University, Burnaby, BC, Canada
Contact person: matt@sfu.ca
INTRODUCTION
This two-part study was conducted to assess the effects of wetting the surface of an
impermeable chemical-biological protective suit on rates of mean body temperature
(MBT) increase during exercise. In part one of the study, estimates of heat loss with a
numerical model were established with a hot plate and manikin. In part 2 of the study,
human exercise trials were conducted to assess the numerical model’s prediction. It
was hypothesized that for exercising humans wearing an impermeable chemicalbiological
protective suit, that there would be reductions in the rate of MBT with
wetting the suit surface and that these lower rates of MBT increase could be predicted
by a numerical model.
METHODS
Study 1: A numerical model was constructed which takes into account heat transport
from skin to inner surface, inner surface to outer, and outer surface to environment.
The skin and inner suit surfaces are assumed to be totally wetted and the skin
temperature fixed. The outer surface can be either wet or dry. The key equations are
for the heat balance at the inner and outer surfaces:
hc12{TSK-TINNER} + Hv hm12 {CS(TSK)-CS(TINNER)} – hc23{TINNER-TOUTER} = 0
hc23{TINNER-TOUTER} – hc34{TOUTER-TAMBIENT} - Hv hm34 {CS(TOUTER)-CS(TAMBIENT)}
= 0
where hc and hm refer to heat and mass transfer coefficients from one surface to the
next (1=skin, 2=inner, 3=outer, 4=ambient), Hv is the latent heat of vaporization of
water, and CS(T) is the saturation vapour concentration of water at temperature (T).
These are transcendental equations for unknowns TINNER and TOUTER which were
solved numerically. With the temperatures known, the heat loss from the skin can be
calculated as follows:
QSK = hc12{TSK-TINNER} + Hv hm12 {CS(TSK)-CS(TINNER)}
Study 2: To assess the numerical predictions of heat loss from the model and manikin
study, 8 participants (average (SD) age: 21.5 (1.0) yrs, weight: 77.7 (4.4) kg, height:
1.18 (0.23) m) walked at 25% of maximal heart rate (HRmax) on a treadmill in a
climatic chamber at 30°C and 30% RH. Exercise was terminated if: the 2 h trial was
completed, age-predicted maximum HR or a rectal temperature (Tre) of 39.0°C were
achieved, or if participant felt too hot or fatigued and voluntarily chose to stop the
trial. Skin temperature was measured on the upper arm, chest, and thigh. Each
participant completed 3 trials. One trial was while wearing a dry- and another trial
was while wearing a wetted- impermeable chemical-biological protective suit and 2
173