Fitra: Addressing the problem of inadequate N95 respirator fit
Hundreds of millions of N95 passive respirators were purchased by the State of California to address the PPE needs of clinical care providers for the COVID-19 pandemic. All of these N95 respirators are NIOSH approved as N95 protection level masks. Understanding what the NIOSH certification means was the key in how the Keck Medical Center of USC achieved a remarkably low infection rate.
NIOSH rating of N95 respirators are in essence a test of material filtering capabilities. The testing criteria includes the sealing of the respirator being tested to a round form and then conducting a particle challenge using sodium chloride particles and a particle counter. NIOSH does not test the fit of these disposable N95 respirators. In order for any respirator to function, two key factors need to be observed. The first is the filter material must stop the penetration of particles at a prescribed rate. All NIOSH N95 certified respirators (barring counterfeit and manufacturer-made defects) are assumed to filter particles at N95 standards. The second is the fit of the respirator must seal to the user’s facial structure. Fit is not accounted for under NIOSH certification. Fit is tested at the end user level using either a chemical taste test or a particle counter as part of OSHA standards. What became clear during the shortages of the COVID-19 pandemic was that respirator fit was just as important a consideration as N95 certification.
Quantitative fit testing performed at the University of Southern California showed that several of these respirators did not adequately fit most wearers. While the material in the device could filter particles at N95 levels, without a proper seal around the face, the wearer remained at risk of increased exposure to the virus. By ensuring that respirators were properly fit using a quantitative fit testing device, Keck Medical Center of USC achieved a 0.27% infection rate of spread from patient to clinical staff, a remarkable order of magnitude decrease in comparison to other medical facilities at 5.5-7.7% infection rates by the end of July 2020 as determined through contact tracing.
This talk introduces the Fitra, an open-source 3D printable frame that can be placed over a poorly fit N95 respirator to increase the chances of a proper fit. Thirty eight volunteers underwent fit testing. The overall fit pass rate was 100% for the 3M model 1860 masks, 50% for the 3M model 8511 masks, 13% for the BYD CARE model DE2322, and 7% for the Honeywell DC300N95. When using the Fitra, the overall passing rate increase to 87% for the DE2322 + Fitra (P < 0.01) and for the DC300N95 + Fitra the passing rate increased to 73% (P < 0.01).
We present the Fitra as an open-source solution to improving fit for two respirators, the BYD CARE model DE2322 and the Honeywell DC300N95.
