The fit factors (FFs) of 10 widely used N95 FFRs had poor fitting characteristics for participants in this test. The geometric mean FFs of all respirators were 15.4 with range from 5.7 to 74.0. The passing rates (0% to 44.7%) of quantitative fit test for all 10 models of FFR were 7.8% and all were below 50%. Two models of D1 and D2 fit better than other respirators but their geometric FFs were still less than 100. The results showed that 27 of 50 participants could not find appropriate FFRs among these 10 common models in the market. This study indicated that widely used N95 FFRs in China didn't fit well and can't provide desired protection for respirator users.
We used Chinese respirator fit test panel representing current Chinese civilian adults to select the participants for this study. The differences of average anthropometric dimensions for 50 participants in this study and those for 3000 Chinese in a previous study 
were minimal. That means the participants in this study could represent Chinese adults well. Mean face width and face length for American males were reported to be 143.5 mm and 122.7 mm, and 135.1 mm and 113.4 mm for females 
. The face width (146.1 mm for male and 138.9 mm for female) of this study were wider than American, and the face length (118.2 mm for male and 110.9 mm for female) for Chinese adults were shorter than American 
. Face length and face width are main indexes used for defining the panel for half-facepiece respirators 
. Although difference of face width and face length exists between American and Chinese, FFRs in Chinese market were designed according to US LANL panel. And our previous study found that LANL panel could not cover 20.9% of Chinese adults 
. The current study confirmed the role of respirator fit test panel in FFR design because we observed that 54% participants could not find appropriate FFRs designed by LANL. Inappropriate panel might be the major reason for low FFs of 10 models of FFR in this study. Similar results were reported by Spies and his colleagues in South Africans 
. They found that 86% subjects couldn't pass the fit test when wearing a medium-sized respirator which designed based on LANL panel, although 29 volunteers in their study were randomly recruited.
The second reason for low FFs of 10 models of FFR is leakage. Filter penetrations for most respirators were below 0.1% and its contribution to IL was small. Thus, face seal leakage is a major factor which contributes to IL. And high value of IL directly induces low FF for a respirator. The participants felt that most respirators had a serious leak around the edge of FFRs, especially at the nasal and chin region. Similarly, Oestenstad et al. observed that about 89% of all observed leaks occurred at the nose or chin or were multiple leaks 
. Han and his colleagues also found that the main route leakage for FFRs may not be the filter medium but the face seal 
Another reason for low FFs of 10 models of FFR might attribute to the size of respirator. The most of FFRs in the market only have one size, medium. It is well known that one universal respirator is difficult to fit all users 
, even if the quality of the material is very good.
The results of this study indicated that self-feeling for leakage of the N95 FFRs was not reliable. About 39.0% of the time, users with self-feeling of no leakage can't pass fit test. For this reason, we suggest conducting fit testing before selecting N95 FFRs. On the other hand, training in FFRs donning has greatly improved the FF in this study. U.S. federal regulations require the employers to provide fit testing and effective training to employees so they can understand the need, use, limitations, and capabilities of the respirators they wear 
. However, little professional training in respirator donning is conducted in China and other countries 
, to the best of our knowledge. Thus, the results from this study suggest that government agencies or occupational safety and health organizations should propose a measure to strengthen the training in FFR donning. It is recommended to develop or complete current standard of selection and using respiratory protective equipment 
These findings have important public health implications. N95 FFRs are trusted and very commonly used in China and other countries. The users believe they will get enough protection by N95 FFRs when they enter working environment with industrial dusts or infectious aerosols. However, if the passing rates of quantitative fit test for FFRs widely used in China are below 50%, we have to worry about the protective effect of N95 FFRs. These results underscore an urgent need to establish regulations on conducting the qualitative or quantitative fit testing when users choose FFRs and training for FFRs donning.