Comparing the Association between Wet Bulb Globe Temperature (WBGT) and Heat Stress Score Index (HSSI) Thermal Indices with Physiological Parameters in a Melting Plant

Exposure to heat is one of the workplace risk factors, which may lead to thermal strain, such as rising heart rate and body temperature. To have the best association between a heat stress indices and physiological parameters have always been a major concern for those studying the subject. This study aims to compare the association of two heat stress indices with physiological parameters. This cross-sectional study was conducted on 54 acclimatized mail subjects working in a steel complex in May 2014. After enrolling individuals based on inclusion criteria, HSSI and WBGT heat indices and physiological parameters were recorded at three times (10 am, 12 pm and 3pm) during their work shift. Then the relationship between physiological parameters and the calculated indices were determined. The study population had a mean age of 29.3±4.2 years. The average value of the WBGT index was 27.3 ± 2.9°C and HSSI index was 22.7±3.6. The average relative humidity and air velocity was 35.9 ±1.9% and 1.5±0.4 m/s respectively. The correlation between WBGT and tympanic temperature was statistically significant (P≤0.01). However the HSSI was not significantly correlated to tympanic temperature (p=0.37). Correlation coefficient between WBGT and HSSI with heart rate was 0.458 and 0.191 respectively. WBGT is likely to offer a better assessment of thermal stress in comparison to HSSI in melting industry workers.