以採樣器與環境風向夾角之觀點探討可吸入性氣膠採樣準則之合理性

A Critique on the Inhalable Aerosol Sampling Criterion-from the Aspect of the Orientations of Aerosol Samplers

現今國際上公認之可吸入性氣膠採樣準則，係假設勞工與風向間之夾角之時間分布為3600均勻分布﹔因此現階段所謂可吸入性氣膠採樣器（如IOM 個人可吸入性氣膠採樣器）在開發時，均以符合角度方向平均之氣膠採樣準則為原則。然而有鑒於勞工作業環境中實際工作時並非呈角度方向平均，因此在不同角度分布情形下，所謂可吸入性氣膠採樣器之採樣結果，是否能代表勞工實際之氣膠吸入量，仍有待進一步探討。本研究先以半經驗氣膠吸入預測模式推估人體頭部、可吸入性氣膠採樣器（IOM）、及總氣膠採樣器（37-mm 濾紙匣），在四種不同環境風速（0.5、1.0、2.0、4.0m/s）及在五種不同環境風向方位（以人體頭部對環境風向之夾角（θ）之範圍來區分，包括0≤θ<π/2, π/2≤θ<π, π≤θ<3π/2, 3π/2≤θ<2π及角度方向平均）時之吸入效率。結果發現，就理論推估而言，在任何角度方向之情形下，37-mm採樣器之捕集結果均無法代表勞工之可吸入性氣膠。在環境風速小於2m/s時則發現IOM 採樣器在面對著環境風向（即0≤θ<π/2及3π/2≤θ<2π）時，與人體頭部之氣膠吸入量有所差異，唯在角度方向平均及背對著環境風向（即π/2≤θ<π及π≤θ<3π/2）之情形下，發現與人體頭部之吸入量一致；在風速為4m/s時，則發現IOM 在任何情形下均有低估可吸入性氣膠測值之現象。因此本研究建議在採用IOM 個人採樣器在高風速（環境風速大於2m/s）實施可吸入性氣膠採樣時，或採樣器與環境風向未呈角度方向平均時，均需予以特別留意。本研究第二部分嘗試以某耐火磚廠之一組實測氣膠採樣資料為例，利用氣膠吸入效率預測模式，探討IOM 及37-mm 濾紙匣捕集氣膠量之差異性。研究結果發現IOM 與37-mm 採樣結果之差異性，並無法以角度方向平均之情形來解釋，而當以採樣器均為背對著環境風向時則方足以解釋其差異性。最後本研究建議現今可吸入性氣膠準則除需考慮角度方向平均之吸入效率外，亦需進一步考量環境風向夾角對可吸入性氣膠吸入效率之影響。

Current internationally recognized “inhalable aerosol sampling criterion” assumes that a worker’s orientations with respect to the environmental wind direction are uniformly distributed with time. Thus, the development of inhalable aerosol samplers (such as IOM personal inhalable aerosol sampler) are required to comply with such a criterion. However, since a worker’s orientation might not be orientation-averaged in real situations, whether the so-called inhalable aerosol sampling results under non-orientation-averaged situations can represent a worker’s exposures requires further investigation. In the first part of this study, semi-empirical aspiration efficiency predictive models are used to estimate the aspiration efficiencies of human heads, IOM personal inhalable sampler, and 37-mm cassette personal sampler theoretically under 4 wind speeds (0.5, 1.0, 2.0, and 4.0 m/s) and 5 phases (based on the range of orientation (θ) of human head with respect to the wind, including 0≤θ<π/2, π/2≤θ<π, π≤θ<3π/2, 3π/2≤θ<2π, and orientation-averaged). The results show that under no circumstances the 37-mm sampler can be regarded as an inhalable aerosol sampler. Under low wind speed situations (≤ 2m/s), the performance of IOM personal sampler falls within the tolerance bands of the aspiration efficiencies of human heads at the orientationaveraged situation and under backward facing phases (i.e., π/2≤θ<π and π≤θ<3π/2). However, it fails at the forward facing phases (i.e., 0≤θ<π/2 and 3π/2≤θ<2π). For wind speed at 4m/s, the collections of IOM samplers tend to under-estimate the inhalable aerosols at all situations. Hence, it is recommended that IOM personal samplers should be used with caution both at higher wind speeds (>2m/s) and at non-orientation-averaged situations. The second part of this study involves the use of aspiration efficiency predictive models to examine the difference between the personal sampling results obtained by using IOM and 37-mm cassette sampler at the mixing area of a refractory brick manufacturing plant. The results show that the differences of both personal sampling data can not be explained as assuming that both samplers were under orientation-averaged situations. Instead, the difference can best be explained as assuming both sampling systems were at backward facing phases. It is concluded in this study that current inhalable aerosol sampling criterion should not only consider the aspiration efficiency under orientation-averaged situation, but should also take the effects of aspiration efficiencies on sampler’s orientations with respect to wind direction at other situations into consideration.