Graduation Year


Document Type




Degree Name

MS in Public Health (M.S.P.H.)

Degree Granting Department

Public Health

Major Professor

Thomas E. Bernard, Ph.D.

Committee Member

Rachel Williams, M.D.

Committee Member

Alfred Mbah, Ph.D.


occupational, prevention, sensitivity, specificity


The U.S. military currently uses a flag system based on wet-bulb globe temperature (WBGT) and metabolic rate to recommend heat stress exposure limits. This paper addresses the ability of the flag system to recommend safe heat exposures in a non-military population.

Two progressive heat stress studies provided data on 528 observations of safe or unsafe exposures of 4 hours over a range of WBGT conditions and metabolic rates using 29 participants wearing woven cotton clothing. For the two studies, range of WBGT conditions was 25 to 42C, and the range of metabolic rates was 100 to 650 watts. These exposures were compared with the flag system’s recommendations of safe exposure to determine the sensitivity and specificity of the flag system. A separate study provided 62 observations with participants undergoing a time-limited protocol at constant WBGT conditions. Observed durations of safe exposure time were compared to the flag system’s recommended safe limits to determine sensitivity and specificity.

Based on the progressive protocol, sensitivity and specificity of the flag system for five ranges of WBGT and three categories of metabolic rate were 0.98 and 0.25, respectively. For the time-limited protocol, which applied only to the highest range of WBGT and light and moderate metabolic rate, both sensitivity and specificity were zero.

This study suggests that the flag system has high sensitivity but low specificity for long duration exposures, along with low sensitivity and specificity for time-limited exposures. However, the WBGT exposures in the time-limited trials were substantially higher than the threshold for the highest WBGT range in the flag system, which may account for the system’s unexpected performance in the time-limited protocol.