2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
NON-EVAPORATIVE EFFECTS OF A WET MID LAYER ON HEAT
TRANSFER THROUGH PROTECTIVE CLOTHING
Peter Bröde 1 , George Havenith 2 , Xiaoxin Wang 2 and THERMPROTECT network 3
1 Leibniz Research Centre for Working Environment and Human Factors (IfADo), Germany
2 Department of Human Sciences, Loughborough University, Loughborough, UK
3 V. Candas, E.A. den Hartog, B. Griefahn, I. Holmér, H. Meinander, W. Nocker, M. Richards
Contact person: broede@ifado.de
INTRODUCTION
Wet clothing can increase the wearer’s heat loss by increasing the thermal conductivity,
which increases dry heat loss (Chen et al., 2003), and by evaporation from the surface or
within the clothing, possibly combined with increased condensation in outer layers (Lotens et
al., 1995). These mechanisms occur simultaneously and are difficult to be assessed separately,
as evaporative efficiency may differ from unity with protective clothing (Candas et al., 2006).
Concentrating on the non-evaporative effects, this paper describes experiments performed
with a manikin and humans, in which two layers of underwear, separated by a layer with low
vapour permeability, were worn under an impermeable overgarment. Wetting the underwear
layer beneath an impermeable outerwear should facilitate the observation of conductive
effects with only minimal influence by evaporation through, and from the outer clothing.
METHODS
To reduce evaporation, humid conditions were chosen: air temperature 20°C, relative
humidity 80%, wind velocity 0.5 m/s, globe temperature was equal air temperature.
Manikin experiments: Heat loss was measured using a thermal manikin ‘Newton’ with 32
independent zones in which surface temperature was controlled at 34ºC. Two layers of Cotton
(CO, producer: Gnägi) underwear were used. Each layer had a separate shirt and long-legged
pants. The two layers were separated by a layer of Tyvek®, which prevented wicking of the
moisture between layers but did allow some evaporative exchange. As the outer layer, an
impermeable garment was used made of PVC. Each of the CO layers was alternately wetted
with 600 g of water, and additional measurements were performed with both layers either dry
or wet. All measurements lasted 40 min, and were performed twice.
Human experiments: Eight healthy male students (22.8 ±1.3 y (SD), 1.81 ±0.06 m, 75.1 ±6.6
kg), gave written consent to participation in two trials each inside a climatic chamber, that had
been approved by IfADo’s ethics committee. The clothing configuration was slightly changed
compared to the manikin study, and comprised polypropylene underwear (HHS, Helly
Hansen Super Bodywear® 140 g/m 2 ), followed by a Tychem® C suit, that prevented both
wicking and evaporation, and the same additional CO mid layer and impermeable PVC outer
layer as used with the manikin. Trials were performed with the CO mid layer either dry or
wetted with 618 ± 16 g of water.
Each trial consisted of 3 phases, each lasting 30 min and separated by a 3-min period where
the fully clothed person’s weight was taken, yielding the mass loss due to evaporation (me)
for that bout. Phase 1 comprised 2 min of treadmill walking (4.5 km/h, level) for an initial
moisture and temperature distribution inside the clothing, followed by 28 min standing to
minimise sweat production. In phases 2 and 3, subjects performed continuous walking.
Heart rates (HR), rectal (Tre) and mean skin temperatures ( T sk ), as calculated from
measurements at 8 body sites, as well as temperature (Tmc) and relative humidity (RHmc) in
216