The Effect of Thermal Factors on the Measurement of Wet Bulb Globe Temperature

綜合溫度熱指數測定評估影響因素之探討

莊侑哲(Yow-Jer Juang) ； 林宜長(Yi-Chang Lin)

《勞工安全衛生研究季刊》 15卷3期 (2007/09) Pp. 191-203

https://doi.org/10.7005/JOSH.200709.0191

摘要

綜合溫度熱指數(WBGT)是由自然濕球溫度、黑球溫度與乾球溫度（只有在戶外有日曬時需採用）之測值計算求得，可提供熱環境快速且有用的熱壓力評估指標，並已被我國採用當作高溫作業判定之基準。本研究的目的係利用可以控制環境參數之熱暴露艙並搭配架設可控制表面溫度之加熱板來模擬輻射熱源，藉以探討影響自然濕球溫度與黑球溫度測定誤差的因素。首先評估不同的黑球尺寸、輻射溫度與環境參數（氣溫、風速與相對濕度）對黑球溫度測值之影響及評估其回應時間，其次則是評估在不同氣溫、風速、相對濕度與輻射溫度條件下之自然濕球溫度測值變化情形。研究結果發現，當有輻射熱源存在時，黑球的尺寸與輻射溫度愈大其黑球溫度測值也愈大，並且隨著黑球尺寸的加大，其回應時間也愈長；而風速愈大則將使其測值變小，如僅有相對濕度改變時則對黑球溫度測值無影響。在風速小於2.60m/s之所有測試條件下，自然濕球溫度均較通風濕球溫度測值大；而且自然濕球溫度測值隨氣溫、相對濕度與輻射溫度增加而增加，但隨風速增加而降低。當熱環境的氣溫大於皮膚溫度並伴隨有明顯的輻射熱源存在時，則風速愈大會造成自然濕球溫度、黑球溫度測值與綜合溫度熱指數愈低而導致熱壓力評估的判斷錯誤。因此，建議在採用綜合溫度熱指數當作熱壓力評估指標時，氣溫大於皮膚溫度時需將風速測定列入考慮。

關鍵字

熱壓力評估 ； 黑球溫度 ； 自然濕球溫度 ； 綜合溫度熱指數

並列摘要

The wet bulb globe temperature (WBGT) can be evaluated by measuring the globe temperature (Tg), the natural wet-bulb temperature (Tnwb), and the air temperature (Ta, only with solar radiation outdoors) to provide a fast and useful index of heat stress in hot environments. For the past few decades, the WBGT has been used as the standard for protecting workers in hot environments in Taiwan. The aim of this paper is to investigate measurement errors in Tnwb and Tg. All the tests were conducted in a climate chamber where the environmental factors (Ta, RH, Va) were controlled in order to study the effect of globe size and radiator temperature (Tp) on Tg, Tnwb, and WBGT. A greater globe size yielded higher Tg measurements for different Va and Tp with significant radiation. The response time of Tg increased with globe size and decreased with air velocity for all test conditions with radiant heat. The measured values of Tnwb under all experimental conditions was greater than the psychrometric wet bulb temperature (Tpwb) estimated by the ambient vapor pressure and air temperature in different combined conditions. Air velocity (Va) is critical for the globe temperature and natural wet-bulb temperature measurement, which can cause errors in heat stress evaluation when the air temperature is greater than skin temperature with significant radiant heat.

並列關鍵字

Heat stress evaluation ； Globe temperature ； Natural wet bulb temperature ； WBGT index

參考文獻

ISO(1989).Hot environments-estimation of the heat stress on working man, based on the WBGT- index (Wet Bulb Globe Temperature).Geneva:ISO.

Yaglou CP,Minard CD(1957).Control of heat casualties at military training centers.AMA Arch Ind Health.16,302-316.

Kerslake D.(1972).The stress of hot environments.Cambridge:Cambridge University Press.

Minard D,Goldsmith R,Farrier PHLambiotte BJ(1971).Physological evaluation of industrial heat stress.Am Ind Hyg Assoc J.32,17-28.

Counsel of Labor Affair (CLA)(1998).Standard of work-rest regimen for worker in hot workplace.Taipei:CLA.