Findings from this small study suggested that a qualitative fit test alone is unable to fully assess mask integrity and that at the doses required for sterilization, gamma radiation degrades the filtration efficiency of N95 masks.
- A set of 3M 8210, 1805, and 9105 masks were irradiated using a cobalt-60 irradiator at the Massachusetts Institute of Technology. Three masks of each type received 0 kGy (control), 1 kGy, 10 kGy, and 50 kGy of approximately 1.3 MeV gamma radiation from the source, at a dose rate of 2.2 kGy per hour.
- Three different particle sizes—0.3, 0.5, and 1 μm—were tested, and the single-pass filtration efficiency was measured using an optical particle counter (Aerotrak 9306; TSI Inc). The measurement system, which was not calibrated for N95 mask certification, was only used to assess the relative changes in the filtration efficiency.
- All masks (both control and irradiated masks) passed the qualitative fit test.
- There was statistically significant degradation of filtration efficiency for treated masks.