Last Revised: January 12, 2022
FITTED VERSUS NON-FITTED N95 RESPIRATORS
Fit tested N95 respirators filter out at least 95% of airborne particles. Fit testing ensures that there is minimal leakage around the edges of the respirator when a user inhales. Leakage can cause ambient particles to bypass the respirator filter and enter the persons breathing zone.
In a CDC, Morbidity and Mortality Weekly Report, non-fit tested N95 respirators were found to have an average penetration of ambient particles of 33%, compared with 4% of the ambient level in fitted masks.1 In a recent Nature article, using a computational model that predicted changes in infection dynamics due to respirator leakage, results suggested that non fit-tested respirators offered some level of protection and lowered the infection rate (from 97% fit tested to 42%—80% non-fit tested). 2
References
1. Anonymous Laboratory performance evaluation of N95 filtering facepiece respirators, 1996. MMWR. 1998;47:1045–1049. [PubMed] [Google Scholar]
2. A computational model for predicting changes in infection dynamics due to leakage through N95 respirators, 2021. Nature, Scientific Reports, 2021:10690.