Ideally N95 masks are disposable and should be used only once and then discarded. However, these masks are in very short supply during the COVID-19 pandemic and most providers are reusing their N95 masks for weeks at a time.
Keep in mind that the SARS-CoV-2 virus is 0.12 microns in size and most bacteria are 3 microns in size. N95 masks filter 99.9% of particles at 0.1 micron in size. Practically speaking coronavirus are not transmitted as isolated virus particles but travel via airborne droplets (particles greater than 5 microns) or aerosols (particles less than 5 microns) from asymptomatic or symptomatic patients produced by breathing, talking, singing, coughing or sneezing. In general, N95 masks protect against aerosol and droplet transmission, while surgical masks protect predominantly against droplet transmission. In turn surgical masks are considered by some as providing twice the protection as cloth masks. One of the best articles re: the transmission of COVID-19 virus by droplets and aerosols can be found here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293495/
With the above said, given that Personal Protective Equipment, especially N95 masks are in short supply – it is in everyone’s best interest to be able to sanitize them. Many hospitals utilize vaporized hydrogen peroxide sanitation systems to sanitize masks. An alternative method is UV-C sanitation which has been demonstrated to kill bacteria, molds and viruses, including coronavirus in a short period of time.
Affordable UV-C sanitizers are available for one item sanitation or micro-wave oven size cabinets that can sanitize multiple items at a time. The single item sanitizers produce a dose of 60 mJ/cm2 ( see file:///Users/andrewschuman/Downloads/jaalas2018000024.pdf), which according to Emergency Care Research Institute (ECRI) will effectively sanitize an N95 mask. These $100 or so devices are sold to sanitize cell phones, with disinfection times that can vary from 3 to 15 minutes. These are available from companies like PhoneSoap, Casetify, Totallee, and others. UV-C cabinets are more expensive, ranging in price from $1200 to $8000 or more depending on size and features. The cabinets have more light output than the single item sanitizers, but the articles I’ve reviewed suggest that phone sanitizers can effectively rid your N95 masks of contagious agents.