Evaluation of DI, WBGT and Swreq/PHS Heat Stress Indices for Estimating the Heat Load on the Employees of a Petrochemical Industry

Heat stress is a common occupational health hazard at outdoor workplaces especially in a hot-humid climate. Overheating of the body can cause a number of problems, including heat rash, heat cramps, dizziness, heat exhaustion, and heat stroke. The present study aimed to assess heat stress indices including DI, WBGT and SWreq/PHS, as a mean to estimate the heat load on the employees of a petrochemical industry. The study was conducted in Pardis Petrochemical Company. All of the ammonia-phase workers (10 men) working in the hot-humid condition were selected and other 11 men workers were chosen from the work sites without risk of heat stress. The physiological parameters such as heart rate, systolic and diastolic blood pressure and deep and skin temperatures and weather parameters, including: Discomfort Index, Wet Bulb Globe Temperature and Required Sweat Rate based on Predicted Heat Strain were measured simultaneously. All of the subjects in two groups as acclimated and unacclimated were monitored in two different weather and working conditions: the work-site and the rest-room. The mean values of the indices and the physiological parameters for both acclimated and unacclimated groups were significantly higher at the work-site than at the rest-room. For WBGT and DI indices, the highest correlation was found with heart rate (0.731, 0.725, respectively). However; the strongest linear relationship existed between SWreq/PHS and deep body temperature (0.766) among the under study heat stress indices. With regard to the data obtained, the SWreq/PHS index had the greatest correlation with deep body temperature, so it can be served as a quick tool to evaluate heat stress for a petrochemical industry like Pardis and appraise the approximate amount of heat strain imposed to the employees.