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., CIH

Co-Major Professor

Steven Mlynarek, Ph.D., CIH

Committee Member

René R. Salazar, Ph.D., CIH


acclimatization, heat stress, occupational exposure limits, sustainable


Heat stress affects thousands of works annually by causing heat-related illnesses. Wet bulb globe temperature (WBGT) is a widely accepted metric to assess the environmental contributions to heat stress. WBGT-based occupational exposure limits (OELs) include the ACGIH TLVs and the NIOSH RELs. The OEL threshold is adjusted downward with increasing metabolic rate. Further, there is an OEL for acclimatized and non-acclimatized workers. An often-recommended intervention found within a heat stress management program is work-recovery cycles to manage exposure. To prescribe work-recovery cycles, the common practice is to use time-weighted averaging (TWA) for the WBGT and the metabolic rate. The purpose of this study was to demonstrate that TWAs for WBGT and metabolic rate are acceptable metrics for assessing exposure and prescribing work-recovery cycles.

A search of the literature found sixteen papers in which there was a protocol that could represent two different exposures. The TWA WBGT and metabolic rate were estimated from the protocol descriptions. The acclimatization state of the participants was noted. Depending on acclimatization state, the TWAs were compared to the OELs and classified as above or below the OEL. The reported physiological outcomes were classified as sustainable or unsustainable using the reported core temperatures. Sustainable was an average at or below 38°C and no individual greater than 38.5°C. Otherwise, the protocol was classified as unsustainable.

Two sets of 2x2 tables were populated from the data, one for acclimatized and one for non-acclimatized, to check for sustainability. For acclimatized participants, there were 19 protocols with a sensitivity of 1.0 and specificity of 0.58. For the non-acclimatized, the lower OEL was used to classify the 57 protocols with the resulting sensitivity of 0.71 and specificity of 0.35. Additionally, 2x2 tables classified by age group (Young, Middle, and Older) were populated with that same data to for check sustainability among acclimatized and non-acclimatized workers.

For acclimatized workers, TWA was shown to be protective with no false negatives observed. For non-acclimatized, the TWA was shown to be protective of most workers, with false negatives, which is considered not as protective. This study demonstrates the effectiveness of TWAs for work-recovery cycles as being protective of acclimatized participants, however they are less protective of non-acclimatized participants, to include Older participants.