Evaluation of Filtration Efficiency Test Method of Surgical Mask
|Keywords:||醫用口罩;次微米微粒過濾效率;細菌過濾效率;Surgical mask;Particulate filtration efficiency;Bacterial filtration efficiency||Issue Date:||2012||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。
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.
|Appears in Collections:||環境與職業健康科學研究所|
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