International Organization for Standardization 7933 standard provides evaluation of required sweat rate (RSR) and predicted heat strain (PHS). This study examined and validated the approximations in these models estimating respiratory heat flows (RHFs) via convection (C ) and evaporation (E) for application to Taiwanese foundry workers. The influence of change in RHF approximation to the validity of heat strain prediction in these models was also evaluated. The metabolic energy consumption and physiological quantities of these workers performing at different workloads under elevated wet-bulb globe temperature (30.3 ± 2.5 °C) were measured on-site and used in the calculation of RHFs and indices of heat strain. As the results show, the RSR model overestimated the C for Taiwanese workers by approximately 3 % and underestimated the E by 8 %. The C approximation in the PHS model closely predicted the convective RHF, while the E approximation over-predicted by 11 %. Linear regressions provided better fit in C approximation (R = 0.96) than in E approximation (R ≤ 0.85) in both models. The predicted C deviated increasingly from the observed value when the WBGT reached 35 °C. The deviations of RHFs observed for the workers from those predicted using the RSR or PHS models did not significantly alter the heat loss via the skin, as the RHFs were in general of a level less than 5 % of the metabolic heat consumption. Validation of these approximations considering thermo-physiological responses of local workers is necessary for application in scenarios of significant heat exposure.

Wang-Yi CHEN, et al.: Factors Associated with Thermal Stresses Imposed on Workers developed in the present study would be beneficial to many other industries for initiating strategies to avert the thermal hazard imposed on workers. (J Occup Health 2014; 56: 505-510)