Applicability of Modified discomfort index (MDI) in Outdoor occupational environments: a case study of an open pit mines in Tehran Province

Regarding development of several thermal indices and limitations of these indexes, in this research we were examined the applicability and validity of Modified discomfort index (MDI) in Outdoor occupational environments.
This cross-sectional study was done on 175 subjects in summer (2016) in 12 mines construction materials of Tehran Province. Environmental and Physiological parameters (oral temperature, tympanic temperature and skin temperature) were measured simultaneously at three periods; also Modified discomfort index (MDI) together with three other Direct Indices include Wet-bulb globe temperature (WBGT), Oxford index (WD) and Wet-bulb dry temperature (WBDT) were calculated. For survey of applicability and validity of Modified discomfort index, the correlation between this index and other Direct Indices at different times of day with Physiological parameters was determined through the Pearson correlation coefficient.
The results showed that MDI index had more correlation with environmental parameters (dry bulb temperature and relative humidity), also very high correlation coefficient with wet-bulb temperature and black-globe temperature. Among the thermal indices used in this study, MDI index had more correlation coefficient with three other indices. On the other hand; MDI had the highest correlation coefficient with oral temperature and the higher correlation with the tympanic and skin temperature after the WBGT index. In all cases, there was a very good correlation between MDI and other indicators at different times of day.
It can be concluded that MDI, despite being simple, lack of need for sophisticated equipment to measure, having a high correlation with physiological parameters, low cost and easy interpretation can be used as substitute for the WBGT index in the range of temperature and humidity study.