Abstract: Objective  To test the filter efficiency and respiratory resistance of N95 medical mask, surgical masks and gauze masks（12 layer and 24 layer）before wear, test the filter efficiency and respiratory resistance change of N95 masks with different wearing time，and to provide a guidance for respiratory protection of respiratory infectious diseases.  Methods  Filtration efficiencies and respiratory resistances of 52 D32-N95 medical masks, 50 general surgical masks，42 12-layer gauze masks and 51 24-layer gauze masks, which were all produced by a science and technology development company were tested before wear by TSI-8130 produced by TSI Company of United States, the test method was the same as that used by NIOSH-N95 and National standard GB 19083-2010. N95 masks were worn half day, 1 day, 2 days  until 7 days  and 14 days（Taking four hours of woking time as 0.5 day） respectively, the filtration efficiency and respiratory resistance were tested within one hour after wear.  Results  The filter efficiency of N95 masks was 97.4%， 32.3% for 12-layer gauze masks, 43.9% for 24-layer masks and 18.4% for surgical masks, the differences were statistically significant (F=4511.5, P<0.05). N95 masks’ filtration efficiency were still more than 95% after wearing two days, more than 90% on the sixth day and more than 80% on the fourteenth day. According to the mathematical model, the filter efficiency of N95 masks was still higher than that of 24-layer of gauze masks (43.9%) after wearing 45 days. The respiratory resistances of different masks changed little and were less than 14 mmH₂O (1 mmH₂O=0.0098 kPa) on the fourteen day, which were lower than the national standard of 35 mmH₂O.  Conclusion  The filter efficiency of N95 mask is much higher than those of gauze masks and surgical masks, it can be used for longer time, and can be used in the field of respiratory disease control.

Key words: Mask, Time, Filtration, Efficiency, Airway resistance