高溫暴露評估技術及高溫與噪音共同暴露健康效應研究

Abstract

熱壓力在大多數位於熱帶及亞熱帶地區的國家及其工作環境已是一個普遍存在具有季節性的職業與環境衛生問題，尤其是像台灣這種既熱且濕的地理環境，要如何避免因熱壓力引起的相關疾病，一直是環境衛生實務工作者必須面對的問題。本論文的研究目的主要是利用自行設計以冷凍庫板所建造之熱暴露艙，在進行穩定性與均勻性評估後，探討高溫暴露評估技術，並配合搭設放音系統進行高溫與噪音共同暴露之健康效應之研究。 高溫暴露評估技術的研究部分，首先在不同環境參數組合的81種實驗條件下，評估其對自然濕球溫度及標準黑球溫度測值的影響，其次則是同時測定131組實驗條件之氣溫、相對濕度、黑球溫度、風速與自然濕球溫度，利用Statistica 6.0統計軟體進行複回歸分析，建立自然濕球溫度之預測模式，並配合利用既有的氣象因素加上黑球溫度測值求得綜合溫度熱指數之預測值供民眾參考以預防熱危害之可行性。 高溫與噪音共同暴露之健康效應之研究部分，則利用熱暴露艙架設放音系統模擬高溫與噪音同時暴露之環境，徵求志願受測者至公立醫院實施健康檢查後進行本實驗，本研究係採用田口實驗設計法將綜合溫度熱指數、噪音音壓級、暴露時間與工作負荷量四項變數利用L9 的直交表進行高溫與噪音共同暴露的暫時性聽力損失之探討。 高溫暴露評估技術的研究結果發現，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2.60 m/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。同時針對開發自然濕球溫度預測模式部份，經複迴歸分析後，發現自然濕球溫度與環境參數具有高度之相關性，其複迴歸方程式為Tnwb = 0.81×Ta + 0.05×Tg + 0.15×RH - 0.35×Va - 9.98 (R=0.996)。經初步驗證，本研究所開發之自然濕球溫度預測模式其預測值與實測值的誤差均小於1 ℃。又利用熱暴露艙探討高溫與噪音共同暴露效應的研究發現，暫時性聽力損失程度主要是取決於噪音暴露劑量並會受到工作負荷與高溫同時暴露而導致聽力損失的增加，並且暫時性聽力損失的恢復時間則由噪音暴露後的損失程度所決定。 綜合上述，利用本研究所開發之綜合溫度熱指數之預測模式，提出以綜合溫度熱指數當作高溫氣象預報指標供大眾媒體預防熱相關疾病之參考，並建議國內因應全球氣候暖化的問題，應積極進行高溫與其他環境的化學因素或是物理因素共同暴露效應的相關研究。

The heat stress is one of major occupational and environmental health issues for workers and residents in the tropical and subtropical areas. The prevention of heat-related illness caused by heat stress is always the important topic for occupational hygiene practitioners, especially in Taiwan with hot and humid climate. The aims of this study are to develop the assessment techniques for thermal exposure of and health effects with simultaneous exposure to heat and noise. A climate chamber made of steel plate packed with polyurethane foam was optimized and used for the experiment. For the thermal exposure assessment technique, we first developed 81 experimental conditions of different environmental parameters to evaluate effects of natural wet bulb temperature and globe temperature. Second, 131 sets of experimental data including air temperatures, relative humidities, globe temperatures, air velocities and natural wet bulb temperatures were generated with the prediction model of natural wet bulb temperature and analyzed using multiple regression analysis. Designed thermal and noise exposure conditions were simulated in the chamber to study the combined effects among volunteers who had received medical examination before the experiment. The L9 orthogonal array of different levels of wet bulb globe temperature, noise intensity, exposure duration and workload was determined by adopting Taguchi’s method. It was found that globe temperature increases with the size of globe and radiant temperature when radiant heat appears, but decreases with the increasing air velocity. However, the change of relative humidity has no effect on the measurement of globe temperature. In addition, the increasing response time of globe temperature is observed for greater globe size. For air velocity smaller than 2.60 m/s, natural wet bulb temperature was found to be greater than psychrometric temperature. And measurement of natural wet bulb temperature will increase with air temperature, relative humidity and radiant temperature, but the trend is reversed when air velocity increases. Therefore, greater air velocity will result in smaller natural wet bulb temperature, globe temperature and wet bulb globe temperature, which leads to the misjudgment on heat stress. According to multiple regression analysis, it was found that natural wet bulb temperature is highly correlated with the environmental parameters. The prediction model is expressed as Tnwb = 0.81×Ta + 0.05×Tg + 0.15×RH - 0.35×Va - 9.98 (R=0.996), and the error is within 1 ℃. From the investigation of combined effects of heat and noise and workload exposure, it was observed that the temporary threshold shift driven by noise exposure is enhanced by heat and workload. The recovery time of temporary threshold shift is determined by the degree of hearing loss after noise exposure. In conclusion, this study proposed wet bulb globe temperature obtained by prediction model as a heat stress index for the prevention of heat-related illness. Further research on health effect induced by combined exposure of chemical and physical agents are suggested to meet the problem of global warming.