RESUMO
The purpose of this study was to determine the level of heat stress to construction workers using Thermal Work Limit [TWL] and Wet Bulb Globe Temperature [WBGT] indices and by measuring Urine Specific Gravity [USG] among construction workers in Iran and comparing the appropriateness of these indices for measuring heat stress in Iran climate. This comparative and experimental study was conducted during September 2012 in Baghe Ketabe Tehran, one of the large size construction sites in Tehran City, Iran. Sixty participants were randomly selected in two groups [exposed to sun and non-exposed] among the construction workers in a construction campus with similar work type, climate and diet. TWL and WBGT and USG were measured in two consequent days and at the beginning, mid and end of the work shift, for both groups. The mean WBGT index was 22.6 +/- 0.9°C for control group and 27.5 +/- 1.2°C for exposure group, the mean TWL index measure was 215.8 +/- 5.2 W/ m[2] for control group and 144 +/- 9.8 W/ m[2] for exposure group and the mean USG was 1.0213 +/- 0.0054 in control group and 1.026 +/- 0.005 in exposure group. There was a significant difference in TWL, WBGT and USG between exposed and non-exposed group [P<0.01]. Workers were at an allowed level of heat stress. TWL, WBGT and USG measures were significantly correlated; however as TWL level enabled classification based on required intervention, it had some merit over WBGT index