Impact on the fitness of N95 masks with extended use/limited reuse and dry heat decontamination

Substandard use of N95 masks, sometimes combined with dry heat decontamination, lacks safety data. We evaluated the impact of these practices on the fitness of N95 masks. This is a non-human subject research conducted from July to October 2020. 155 masks were used by 12 healthcare workers during 10-hour shifts. Masks were collected at the end of the shift and if the number of donnings/doffings was less than five (‘modified extended use’, ME) or whenever this number reached five (‘limited reuse’, LR), per the recommendation of the Centers for Disease Control and Prevention. Masks that passed an Occupational Safety and Health Administration qualitative fit test underwent a cycle (30 min, 75°C) of dry heat decontamination. After use, 84% (95% CI 77% to 90%) of the masks fit the users, 85% (95% CI 73% to 93%) in ME and 83% (95% CI 73% to 90%) in LR. After dry heat, 86% of the fitted masks (95% CI 78% to 91%) still fit, 93% (95% CI 80% to 98%) in ME and 82% (95% CI 70% to 89%) in LR. If a fit test was not done before decontamination, 72% (95% CI 64% to 79%) of the masks would fit, 79% (95% CI 66% to 88%) in ME and 68% (95% CI 57% to 77%) in LR. Common substandard use preserves fitness of N95 masks up to 85%. One cycle of dry heat decontamination preserves fitness of N95 masks up to 93% when donned/doffed less than five times and fitness is ensured before decontamination. If a fit test is not performed beforehand, dry heat decontamination cannot preserve the fitness of used N95 masks above 80%.