Modifying NIOSH's Manikin Fit Evaluation Method to Match Fit Testing with Human Subjects

A manikin fit test method developed by the Center for Disease Control and Prevention's (CDC) National Institute of Occupational Safety and Health (NIOSH) has been proposed as an alternative to fit testing with human subjects. The advantages of a manikin fit test method over actual fit testing are that it does not require human subjects which can be resource intensive, and hence easier to implement. At the beginning of coronavirus 2019 (COVID-19) pandemic, although early studies showed that manikin fit can be maintained after several decontamination cycles, real world evidence obtained using human subjects revealed that the N95 respirators failed only after a few decontamination cycles. The goal of this article was to make modifications to the NIOSH's manikin fit-test method so it can mimic real world performance of N95 respirators better. After making modifications to this method, we then investigated the effect of long-term wear after donning of the respirators, repeated donning and doffing, as well as decontamination methods (i.e. autoclaving and microwave generated steam) on the fit factor. Averaging the overall manikin fit factor across all scenarios, our modified method overpredicted overall fit factor by only 7 % and 14 % compared to adult human subjects using a breathing routine that included simulated heavy breathing rates of 85, and 70 Liters/minute, respectively. In addition, a constant flow produced similar results as cyclic flow using a breathing simulator. The modified test method also offered the following additional insights into reuse of respirators during future pandemics - when reused within a single work shift, more than 5 donnings should be avoided; and microwave generated steam may be a more viable option for decontaminating N95 respirators compared to autoclaving for a single decontamination cycle.