Graduation Year

2010

Document Type

Thesis

Degree

M.S.P.H.

Degree Granting Department

Environmental and Occupational Health

Major Professor

Thomas E. Bernard, Ph.D.

Co-Major Professor

Candi Ashley, Ph.D.

Committee Member

Steven Mlynarek, Ph.D.

Keywords

heat stress, acclimatization, protective clothing, un-acclimatized, progressive heat stress protocol

Abstract

Clothing directly affects the level of heat stress exposure. Useful measures to express the thermal characteristics are WBGT (wet bulb globe temperature) clothing adjustment factor (CAF) or apparent total evaporative resistance (Re,T,a). The CAF is assigned through laboratory wear trials following a heat stress protocol in which the air temperature and humidity are progressively increased until the participant clearly loses the ability to maintain thermal equilibrium. The critical condition is the point of thermal transition and from these conditions both the CAF and Re,T,a are computed. The first objective of this study is to compare the thermal characteristics of a coverall made from a prototype fabric to work clothes and a commercial limited-use coverall using CAF and Re,T,a. A second objective is to demonstrate that the Re,T,a of work clothes is the same for progressive or steady-state heat stress protocols.

Five participants (4 men and 1 woman) walked on a treadmill at 1.25 m/s at an average metabolic rate of 175 W/m2. Each participant completed at least one progressive heat stress protocols in work clothes, Tyvek® 1422A coveralls [Tyvek® is a registered trademark of DuPont], and a developmental nonwoven polyolefin prototype ensemble provided by DuPont. In addition, four participants completed steady-state protocol in work clothes. Participants did not complete an acclimation period prior to the trials and each trail was separated by at least 40 hours.

There are no within participant differences in metabolic rate among ensembles and protocols. There are no differences between the critical WBGT in the current participants and previously acclimatized participants from other studies suggesting that the participants responded as if they were acclimatized. Based on a mixed effects model, there are significant differences between work clothes and Tyvek® 1422A for Re,T,a (0.0103 and 0.0141 m2/W kPa, respectively) and critical WBGT. The CAF for Tyvek is 2.3 °C-WBGT. For the DuPont prototype ensemble, the apparent total evaporative resistance is 0.013 m2kPa/W and the CAF is 0.5 °C. The prototype ensemble shows no difference from work clothes or Tyvek® 1422A in critical WBGT and no difference from work clothes in Re,T,a. Overall, the prototype coveralls exhibited thermal characteristics that would have a lower level of heat stress than the Tyvek 1422A and not significantly different from work clothes.

The values for Re,T,a for work clothes were not different between the steady state and progressive protocols. The steady-state protocol near the critical condition can be used for determination of Re,T,a. This opens up the possibility of estimating Re,T,a from studies that do not use the progressive protocol.