Examining If The Occupational Heat Stress Recommendations Prevent Core Temperature From Exceeding 38.0 °C.

Heat stress recommendations aim to maintain core temperature (TC) below 38.0 °C in unacclimatized workers. In this secondary analysis, we assessed the recommendations when: 1) work-rest ratios are adjusted based on wet bulb globe temperature (WBGT) at a fixed rate of metabolic heat production (Hprod) and 2) Hprod is adjusted based on WBGT at a fixed work-rest ratio. We compared this to non-compliant trials that either violated WBGT exposure or work intensity limits. PURPOSE: To test the hypothesis that adhering to occupational heat stress recommendations will prevent TC from exceeding 38.0 °C despite differences in WBGT, Hprod, and work-rest ratios. METHODS: Unacclimated men and women completed 4-hour (half workday) exposures at a fixed WBGT, Hprod, and work-rest ratio. There were six iterations of Compliant Trials (n = 72 total observations; A: 24.1 °C, 431 W, 60:0 min; B: 26.6 °C, 461 W, 45:15 min; C: 28.4 °C, 462 W, 30:30 min; D: 29.7, 453 W, 15:45 min; E: 27.3 °C, 412 W, 30:30 min; F: 31.6 °C, 290 W, 30:30 min) and two iterations of Non-compliant Trials (n = 24 total observations; G: 36.1 °C, 453 W, 15:45 min; H: 31.7 °C, 410 W, 30:30 min). All subjects were provided 237 mL of sport drink every 15 min and drank ad libitum.Peak TC during the 4-hour exposure is reported. Individual TC responses were fit using linear regression and the resulting equation was utilized to predict peak TC occurring during an 8-hour exposure (i.e., a full workday). RESULTS: Peak TC was lower in the Compliant Trials (37.9 ± 0.3 °C) compared to Non-compliant Trials (38.7 ± 0.5 °C; p < 0.01) and was less than 38.0 °C in 56% of Compliant Trial observations, whereas peak TC exceeded 38.0 °C in all Non-compliant Trials. Peak TC was lower than the hypothetical peak TC of 38.0 °C (p = 0.04). Conversely, the prediction of peak TC during an 8-hour exposure revealed that most Compliant Trials (70%) would exceed a peak TC of 38.0 °C (p < 0.01). However, estimated peak TC remained lower in the Compliant Trials (38.2 ± 0.5 °C) compared to Non-compliant Trials (40.3 ± 1.9 °C; p < 0.01). CONCLUSION: In the 4-hour exposures, peak TC did not exceed 38.0 °C in the majority of occupational heat stress recommendation compliant trials. However, predicted peak TC exceeded 38.0 °C at 8 hours in most trials, albeit at a lower incidence than non-compliant trials. R01OH011528