The effect of gas flow and loading on the filtration performance of the breathing system filters

• Main Authors: Hong-Sheng Hsieh, 謝宏昇
• Other Authors: Chin-Sheng Tang
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/y8r7fn

碩士 === 輔仁大學 === 公共衛生學系碩士班 === 99 === Introduction The pathogens such as virus and bacteria always spread in the air of air conditioned hospital facilities and probably cause infection for patients and health care workers. The breathing system filter (BSF) mounted in the ventilator circuit was used to filtrate bacteria- and virus-carrying aerosols from mechanical ventilated patients. The aim of this study was to evaluate the effect of gas flow and loading on the filtration performance of the BSFs using sodium chloride (NaCl)-containing aerosols. Methods The Collison nebulizer containing 0.5% W/W NaCl solution was used to generate polydisperse aerosols for filter challenge(MMAD:52.95 nm, GSD:1.97). The penetration of particles through each filter was measured using a scanning mobility particle sizer (SMPS) (figure.1) from sized 11.1 to 1083.3 nm. This study selected three pleated hydrophobic filters and three electrostatic filters with different testing conditions (filter loading: 0.2 mg and 0.4 mg NaCl; gas flow: 40, 50 and 60 LPM) for filtration performance evaluation. Results The mean filtration performance was 99.240~99.993% for pleated hydrophobic filters and 73.548~79.050% for electrostatic filters at zero loading and gas flow of 50 LPM conditions.The penetration of electrostatic filters increased as flow increased at the size range between 32.4 and 1083.3 nm, in contrast to the penetration decreased at the size range between 11.1 and 35.5 nm.The penetration of pleated hydrophobic filters increased as flow increased at the size range between 27.0 and 1083.3 nm.The penetration of pleated hydrophobic filters reduced with increased NaCl loading on filters. Contrastly, the penetration of electrostatic filters elevated with increased loading on filters. Conclusion The penetration of the BSFs varied with the loading on filters, the gas flow, and the particle size. The evaluation of filtration performance on BSFs would be insufficient while testing only with 0.3 μm NaCl particle. This study demonstrated that the penetration of particles through BSFs increased as the flow of air through the filter increased, but some particle size (11.1~35.5 nm) of electrostatic filters was opposed. The size of many pathogens wasn’t 0.3 μm, therefore, future studies is necessary to evaluate the filtration performance of BSFs under the various particle size.