2007, Piran, Slovenia

Clothing
TOTAL EVAPORATIVE RESISTANCE USING WEAR TRIALS
FOR FIVE CLOTHING ENSEMBLES
Victor Caravello 1 , Elizabeth A. McCullough 2 , Candi D. Ashley 1 , Thomas E. Bernard 1
1 University of South Florida, Tampa FL, USA
and 2 Kansas State University, Manhattan KS USA
Contact Person: tbernard@health.usf.edu
INTRODUCTION
A progressive heat stress protocol can be used to identify the critical conditions at
which the maximum heat loss, due to evaporative cooling, is balanced by the net heat
gain, due to internal sources and dry heat exchange. These relationships are
illustrated by Equation 1.
(Pa - Psk) / Re,T,r = Hnet + (Tdb - Tsk) / IT,r where Hnet = M - Wext - S + Cres - Eres (1)
The resultant resistance to evaporative cooling (Re,T,r), and the total resultant
insulation (IT,r), are recognized as the two primary coefficients for understanding the
thermal characteristics of clothing. Recognizing that these were two unknowns, the
Penn State group (Kenney and others) proposed a method based on simultaneous
equations to solve for both coefficients using heat balance data from a physiological
method, which provides an method to account for dry heat transfer through wet
clothing and movement of the body. Their method provided a means to relate
environmental and physiological measures at two critical conditions, and hence, the
thermal characteristics could be determined. The USF group (Bernard and others) has
taken the approach of estimating IT,r and using that value to estimate Re,T,r, believing
that estimating evaporative resistance is robust to estimates of clothing insulation. In
this paper, values for Re,T were determined from wear trials using the progressive heat
stress protocol across five different ensembles.
METHODS
Twenty-nine adults participated. Prior to beginning the experimental trials to
determine critical WBGT, they underwent a 5-day acclimatization to dry heat that
involved walking on a treadmill at a metabolic rate of approximately 160 W m -2 at
50°C and 20% relative humidity (rh) for two hours. Participants wore a base
ensemble of shorts, tee-shirt (or sports bra for women), socks and shoes.
Five different clothing ensembles over the base ensemble were evaluated. The
ensembles included work clothes (135 g m -2 cotton shirt and 270 g m -2 cotton pants),
cotton coveralls (305 g m -2 ) and three limited-use protective clothing ensembles:
particle-barrier ensembles (Tyvek® 1424 for half the participants and Tyvek® 1427
for the other half), water-barrier, vapour-permeable ensembles (NexGen® LS 417),
and vapour-barrier ensembles (Tychem QC®, polyethylene-coated Tyvek® ). The
limited-use coveralls had a zippered closure in the front and elastic cuffs at the arms
and legs; and they did not include a hood.
Each ensemble was worn by each participant at a moderate rate of work. Typically the
dry bulb temperature (Tdb) was set at 34°C and relative humidity (rh) at 50%. Once
the participant reached thermal equilibrium (no change in Tre and heart rate for at least
15 minutes.), Tdb was increased 0.8°C every 5 minutes. During trials, participants
137