To obtain basic data for prevention of heat stroke during construction work in a hot environment, we analyzed the effects of wearing ventilated work wear (VWW) and water intake (RWI). First, experiments were carried out with nine male form workers in an artificial climate chamber (AC) at 34°C. Second, measurements were carried out with four male form workers and one male rebar placer at an outside construction site (CS) for four days in August 2017. It was carried out from 8:00 to 17:00 and was divided into four shifts split up by breaks as follows: 8:00 to 10:00, 10:30 to 12:00, 13:00 to 15:00; and 15:30 to 17:00. Activity amount (ACT) was continuously measured. WBGT was measured in the CS. The sweat rate (SR), the rate of naked body weight loss (RBWL, only in the AC), body weight loss while fully clothed (RBWLC), and RWI were each measured and calculated as the difference between the values before and after work per unit time. Evaporation rate (ER) was defined as the sum of RBWLC and RWI. SR in the CS was estimated from the ER by using the regression equation between ER and SR in the AC data.

 In the AC experiment, the SR during work was constant and RBWL was negatively correlated with RWI, those were statistically significant, regardless of whether the workers wore VWW. The RWI and SR of workers not wearing VWW were significantly higher than those of workers wearing VWW. RWI increased significantly and RBWL decreased as ACT increased. This is the reason that RBWL was negatively correlated with the RWI in the AC.

 In the CS experiments, the SR of workers not wearing VWW increased significantly as WBGT increased, but the RWI did not change significantly; as a result, RBWL increased significantly with WBGT. The SR of individuals wearing VWW, which was lower than that of those not wearing VWW, remained almost constant with increasing WBGT, whereas RWI did not increase with WBGT. As expected from these results, RBWL remained constant as WBGT increased and was consistently lower than that of workers not wearing VWW. The ER of works in the CS was significantly higher than that of those in the AC due to the difference between the averaged ACT in the AC (1.8 Mets) and CS (2.4 Mets). In the CS experiments, we estimated the dewatering ratio (DR) by body weight loss while fully clothed (BWLC), since BWL was not measured. The fluctuation during working shifts of BWLC and DR of workers was compared between those wearing and those not wearing VWW on hot two days. In the shifts, the BWLC of workers not wearing VWW was significantly higher than that of those wearing VWW. Furthermore, in the breaks between shifts, the amount of water recovered by workers not wearing VWW was significantly lower than that of those wearing VWW. As a result, after the last shift, the average DR (2.03) of workers not wearing VWW was higher than that of those wearing VWW (1.53).

 We supposed there is a limit to the amount of water that workers in a construction site can drink. Thus, we verified that, in the CS setting, RBWL increased with increasing WBGT mainly due to insufficient RWI, but could be partly decreased by using VWW, which decreased the SR.