Evaluation of Occupational Exposure to Heat Stress and Physiological Responses of Workers in the Rolling Industry

Many indices are used to assess occupational heat stress at the work environments. The aim of this study was to evaluate heat stress using Wet Bulb Globe Temperature (WBGT) index and Discomfort Index (DI), and by measuring physiological responses in the workers of the rolling industry and comparing the appropriateness of these indices for measuring heat stress.

This cross-sectional study was carried out on 90 healthy workers of a rolling industry in eastern Tehran in 2017. Physiological parameters of core body temperature (T_cr) and Heart Rate (HR) were measured during the working shift according to ISO9886 standard. At the same time, environmental variables such as the natural wet temperature (T_nw), dry temperature (T_d) and globe temperature (T_g) were measured and recorded at the workstations. Then, the DI and the WBGT indices were calculated using the related formulae. Data were analyzed using SPSS v. 21, t-test and Pearson correlation coefficient.

The mean heat stress indices were significantly higher in working conditions than resting conditions, and there was a significant difference between the physiological parameters of T_cr and HR in resting and working conditions (P<0.001). According to the screening criteria of DI, 43.3% of the workers were exposed to the moderate level and 56.7% to the severe level of heat stress. There was a significant difference between the mean WBGT and the Threshold limit values (t= 4.903, P<0.001). Pearson correlation test showed that there was a significant and direct linear relationship between the WBGT and the physiological parameters of T_cr and HR (r=0.317, P=0.002; r=0.434, P<0.001, respectively). The DI index had a significant and direct linear relationship with HR; (r=0.229, P=0.03).

The results showed that WBGT is a more appropriate index for evaluating the heat stress of workers in the rolling industry. High heat stress levels at the workstations along with heavy physical activity are health risks for workers in this industry; therefore, interventions must be undertaken to reduce exposure.