What is reasonable re-use criteria for N95 (or P100, etc.) respirators?
Traditionally, “N” respirators are single use, “R” daily 8 hour shift use, and “P” is 30 days use. Under approved “extended use” situations such as this pandemic, any respirator may continue to be used as long as it still fits, the elastics and seal are adequate as determined by a qualitative check of breathing seal (inhale/exhale against your gloved hand), and work of breathing is OK (indicative of filtering mesh not clogged). Avoid touching the inside aspect of the mask. For practical purposes, use of facial cosmetics should be minimized while using the masks and the filtering area should not be written on (identification can be maintained on the exterior of a paper bag used for storage or by an ID on one of the elastic bands).
Recommended guidance for extended use and limited reuse of N95 filtering facepiece respirators in healthcare settings. CDC/NIOSH. Accessed on May 6, 2020 at: https://www.cdc.gov/niosh/topics/hcwcontrols/recommendedguidanceextuse.html