醫用面(口)罩過濾效率檢驗方法之評估

Abstract

日前國內醫用面(口)罩，經衛生署公告自96年7月14日起均須符合國家標準CNS 14774之性能規格要求，該標準中對於口罩濾材的過濾效率方面，規定必須同時符合細菌過濾效率（bacteria filtration efficiency, BFE）測試以及次微米微粒過濾效率（particulate filtration efficiency, PFE）測試等二種方法的性能要求(經濟部標準檢驗局 2003)。由於在進行BFE測試方法時所耗費之時間及耗材都較PFE測試方法來的高，且也有造成生物危害之風險。相對地，PFE測試方法相對容易操作，且可以較快得知測試結果。雖然BFE與PFE的測試條件並不相同，可能使得口罩測試結果有所差異。但從穿透率的觀點來看，對於同一濾材而言，BFE與PFE的測試結果應該會有相當程度的相關性。故本研究目標為建置PFE、BFE方法與評估確認各項變異之來源，建立PFE與BFE的相關性，並利用實驗方法比較BFE與PFE之差異，評估以PFE取代BFE的可能性，其優點為增加醫用口罩性能測試的可靠度，同時降低耗材成本以及時間上的需求。 為了解不同之醫用口罩在BFE與PFE試驗中之差異，本實驗自市面上選取W、H、M三牌款口罩為樣本進行其穿透率曲線之測試。實驗中選取W、H、M牌三款口罩，每款各取15片，共45片口罩為一組進行測試，一共測試兩組口罩，將兩組口罩分別送至美國Nelson實驗室以及財團法人紡織產業綜合研究所，要求以等同CNS 14755之實驗方法的條件進行測試，最後將雙方結果進行比較。另外，本實驗針對影響氣霧產生之相關參數，以相當於單一金黃葡萄球菌粒徑的壓克力粉末模擬BFE試驗氣霧之產生以探討其產生特性。 目前成果發現影響微粒粒徑分布的主要貢獻因子為用於稀釋細菌懸浮液之蛋白腖溶液，蛋白腖溶液濃度越高，所產生的微粒粒徑越大，質量數目濃度也越高。除了蛋白腖溶液之外，產生器供給之高壓空氣流率及溶液供給速率也會影響產生微粒之特性。實驗中模擬細菌懸浮液之壓克力粉末濃度介於104~106 #/cm3，根據結果得知並未對所產生的微粒粒數濃度粒徑分布造成顯著影響，因此推測在BFE實驗時可藉由改變細菌懸浮液濃度改變採集到之菌落數，而不致影響其粒徑分布。此外，結果也顯示改變測試腔中濕度或是否對產生之微粒進行電性中和以及使用不同廠牌之蛋白腖都未顯著影響霧化器產生微粒之特性。 本實驗結果顯示當量測之微粒粒徑範圍與分布情形不同時，微粒的分布情形會對口罩穿透率測試結果造成影響。當挑戰氣膠微粒之CMD落在 3 ± 0.3 μm時，當CMD越小、GSD越大，對於相同濾材來說，其總微粒穿透率也會隨之增加。而穿透率越高的口罩越容易受到挑戰氣膠分布的影響，反之，只要口罩的穿透率夠低，挑戰氣膠分布的影響則可以忽略。當進行BFE測試方法量測同一款口罩之穿透率時，其穿透率結果會較PFE測試方法有較大之變異，將使得BFE之測試結果在各實驗室間之再現性較PFE之方法要低。

Surgical masks need to pass bacterial efficiency (BFE) tests equivalent to ASTM F2100 as required by USFDA, to be certified for medical use in many countries. Yet, surgical mask filter efficiency has been found extremely variable in several previous studies. The inconsistency results among certified laboratories during the inter-laboratory comparison tests were particularly troublesome to the regulatory agencies. Therefore, this work aimed to identify the source of the variability of BFE test method and to propose a replacement method that is more consistent and directly associated with the respiratory protection.

Experimental apparatus was build according to the ASTM F2100. Acrylic powder of 0.8μm was used as the surrogate of Staphylococcus aureus during the beginning phase of the project. Aerosol particles were nebulized into chamber and sampled with an Andersen cascade impactor sampler onto 6 stages at 28.3 L/min. The size distribution and number concentration of the aerosol output were measured using an aerodynamic particle sizer. The filtration efficiency of the surgical masks to be tested by ASTM method, was measured using a scanning mobility particle sizer (for particle smaller than 0.7 μm) and an aerodynamic particle sizer (for particles larger than 0.7 μm). The major operating parameters included concentration of the peptone solution, brand of peptone, number concentration of particle in the solution, solution feeding rate, and air flow supplied to the generator. In addition to the in-house laboratory experiments, two certified laboratories (Nelson laboratory in the United States and Taiwan Textile Research Institute, TTRI laboratory) were chosen to carry out the inter-laboratory comparison. Three models of already certified surgical masks with the lowest filtration efficiency were selected to facilitate the statistical analysis of bacterial colony count. The particulate filtration efficiency and the pressure drop across the filter media were measured by using a filter tester (TSI 8130) before sending to certified laboratories. For each model, 15 facepieces were sent to a laboratory for pressure drop, BFE and PFE tests. The results showed that aerosol number concentration increased with the increasing air flow supplied to the generator. This is because higher air flow (or pressure) tended to break solution into smaller droplets. But the peptone concentration and the solution feeding rate appeared to be the two most influential factors determining the size distribution of the generated droplets. The bacteria (or the acrylic powder) concentration in the solution did not affect the aerosol size distribution, but might change the colony count of BFE test. From the inter-laboratory comparison, the particulate filtration efficiency tests were consistent in terms of pressure drop across the filter media and the aerosol filtration efficiency. However, the bacterial filtration efficiency test results were random and even contradictive. This is likely due to the propagation of the uncertainties embedded in the biological processes of BFE method. Overall, the Bacterial efficiency tests method is inconsistent, tedious, costly and unnecessary. We propose that surgical masks be tested using non-biological particles with the most penetrating size, i.e., 0.3 μm for mechanical filters, and 0.075 μm for electret fitlers.