Nag P K, Ashtekar S P, Nag A, Kothari D, Bandyopadhyay P, Desai H
Ergonomics Division, National Institute of Occupational Health, Ahmedabad.
Indian J Med Res. 1997 May;105:226-34.
The heat tolerance of 11 male volunteers were examined under seven climatic conditions in a climatic chamber. The conditions were 38 to 49 degrees C dry bulb temperature and 45 to 80 per cent relative humidity, i.e., 32.3 to 40 degrees C effective temperature-basic [ET(B)]. The ET(B) values were equated to other heat stress indices, e.g., WBGT (Wet-bulb Globe Temperature Index) and Oxford Index. The subjects did ergometric work at an intensity of 60 per cent VO2max. The exposure durations were decided by the cardiorespiratory, body temperature and sweating responses. Of the climatic conditions studied, at 35.4, 38, 39 and 40 degrees C ET(B), the body core temperature (Tcr) reached over 39 degrees C and heart rates attained 172 to 182 beats/min, which were taken as the tolerance limit. The total oxygen demand significantly varied with the increase in environmental warmth, i.e., increase or decrease of one litre of oxygen demand was equivalent to one minute change in tolerance time. The volunteers were not susceptible to heat; only in extreme hot situations beyond 35.4 degrees C ET(B), were unacceptable levels of physiological and psychophysical reactions seen. The study suggests the acceptable and tolerable limits for human exposure in heat: (i) acceptable at 38 to 38.2 degrees C Tcr for a tolerance time of 80 to 85 min; and (ii) the tolerable limit of short duration (40-45 min) at 39 degrees C Tcr that corresponded to 31.5 and 36.5 degrees C ET(B).
在气候舱内的七种气候条件下，对11名男性志愿者的耐热性进行了检测。这些条件为干球温度38至49摄氏度，相对湿度45至80%，即有效温度基础值[ET(B)]为32.3至40摄氏度。将ET(B)值与其他热应激指标进行了换算，例如湿球黑球温度指数（WBGT）和牛津指数。受试者以最大摄氧量（VO2max）的60%强度进行测力工作。暴露持续时间根据心肺、体温和出汗反应来确定。在所研究的气候条件中，在ET(B)为35.4、38、39和40摄氏度时，人体核心温度（Tcr）超过39摄氏度，心率达到172至182次/分钟，这些被视为耐受极限。总需氧量随环境温度升高而显著变化，即需氧量每增减一升相当于耐受时间增减一分钟。志愿者对热不易感；仅在ET(B)超过35.4摄氏度的极端炎热情况下，才出现了不可接受水平的生理和心理物理反应。该研究提出了人体在热环境中的可接受和耐受极限：(i) 在Tcr为38至38.2摄氏度时，耐受时间为80至85分钟，此时为可接受；(ii) 在Tcr为39摄氏度时，对应ET(B)为31.5和36.5摄氏度，短时间（40 - 45分钟）的耐受极限。
