This paper describes a study of occupational heat exposure in five plants where 12 people were observed. For the assessment of the level of heat stress in these plants, two methods in ISO system of standard, i.e., the WBGT-index (ISO 7243) and the index of required sweat rate (ISO 7933) were used an assessment index of worker’s heat load in the present study. Area heat stress sampling show that the WBGT values ranged from 22.50 °C to 35.80 °C for each of the work positions studied. Furthermore, the data of the time-weight average heat stress indices indicated that 42 % of the subjects (five workers) surpass the limited values of WBGT and CET (Corrected Effective Temperature) recommended by Japan Society for Occupational Health (JSOH), and 58 % of the subjects (seven workers) exceed the limited values of HSI (Heat Stress Index). Therefore, further analyses were performed using ISO 7933, proving the data for determining an acceptable working time. The tolerance times were useful to instruct workers in extremely hot environment, ensure person’s health and safety. In these conditions, 58 percent of the subjects could not continue working in the heat environments, predicted ISO 7933 index. Additionally, the relationships between the value of various heat stress indices and the WBGT index were also correlated in this study. 本研究旨在於探討五家工廠中十二名勞工熱暴露之實況，為評估勞工於作業場所之熱危害，本研究採用國際標準組織(ISO, International Organization for Standardization)推薦的綜合溫度熱指數(WBGT, Wet Bulb Globe Temperature， ISO 7243標準)及需求流汗速率(SWreq, required sweat rate， ISO 7933標準)指標等兩種國際方法，作為勞工熱暴露危害之評估指標。區域熱應力測定顯示，勞工所有工作位置之綜合溫度熱指數(WBGT) 介於22.50 °C至 35.80 °C。經結合勞工工作需求代謝熱、工作位置之實際停留時間及衣著情況等因素，並與文獻推薦之恕限值比較，發現有42 %勞工的熱暴露危害高於WBGT及CET (校正有效溫度)文獻之推薦值；若以HSI (熱應力指數)評估勞工的熱暴露危害情形，顯示勞工中有58 %的人熱暴露超過文獻推薦值。為進一步瞭解熱暴露超過文獻推薦值之勞工的熱暴露危害，同時顧及於極度高熱作業場所勞工之身體健康及生命安全，本研究採取ISO 7933標準估算勞工的容許暴露限制時間，顯示有58 %的勞工不能執行連續性工作。除了ISO 7933及HSI等兩種模式外，本研究亦研討其它數種常用熱應力指標與WBGT之關連性，俾便利於評估極度高熱作業場所勞工熱暴露危害之應用。
