Fit Characters And Temporal Changes Of N95Filtering-facepiece Respirators

Background: N95filtering-facepiece respirators (FFRs) are the most widely usedrespirators recently. Millions of people rely on N95FFRs to reduce industrial dust inoccupational area and prevent particles or infections in medical or atmospheric environment.The fit character (the sealed condition between respirator and wearer’s face) mostly affectsthe protective effect provided by the respirator. In many countries, such as the US, fit testwas necessary conducted before chosen respirators according to their respiratory protectionstandard. Chinese current standards haven’t required fit testing mandatorily. Previousstudies indicate that head facial anatomy have the greatest effect on fit characters ofrespirators. In order to avoid the temporal changes, several contries recommendedconducting fit test termly. Reasonable determination about time interval of fit test is stillcontentious.Objective: To analysis the consistency between objective fit test results of N95FFRsand users’ subject leakage feelings; To investigate the change regulations of fit charactersover time and the reasonable time interval of fit test.Methods: Fit factors (FF) were measured by a quantitative Condensation NucleiCounting method (CNC). A FFR is defined as pass when its FF is greater than100.Representative participants were selected using the Chinese respirator fit test panel. In partone, four Models of N95FFRs and50participants were selected. Fit tests were conductedthree times for each model. Each participant was investigated subjective leakage feelings byquestionnaire. In part two,42participants were included and each participant was selectedone N95FFR with a good fit character according to the result of a CNC fit test（FF≥100）.Fit tests were conducted per half a year and seven times in total three years. For each test, asubject was tested with three replications for each respirator and three respirators for his orher model. The geomeans of FFs (GMFFs) were calculated. The head-and-face indicatorsand body indicators of participants were also measured each time.Results: In the consistency analysis, passing rates of fit test about four models were4%,4%,42%and20%, which were smaller than passing rates of subject leakage feelings (42%,44%,76%and60%). The kappa coefficient was0.067(P=0.18) and the consistent rate was 50%. The results indicated that the consistency was poor. In the study of temporal changes,passing rates were reduced gradually in seven tests and below90%from the sixth time.Almost all participants whose fit test became failure were distributed in small face andmiddle face. After the forth test, GMFFs of large face participants were significant higherthan small and middle face participants. The change for face width and face length hadpositive effects on the change of LNFFs.Conclusions: Users can’t determine fit character of respirators accurately by subjectiveleakage feelings. According to our study, we suggest that the time interval of fit test couldbe defined as two years. Workers who have small or middle faces should obtain moreattention on the temporal change of fit characters. The variations of face width and facelength are the most important indicators affecting temporal changes of fit characters.Regular monitoring of workers’ face width and face length could be built to recognizeobvious changes of FFRs opportunely.