Face Mask Covidefficiency Calculator

Filtration ratings come from standardized bench tests, not from field performance. Under the US NIOSH standard in 42 CFR Part 84, an N95 filter must remove at least 95 percent of a sodium chloride aerosol near the most penetrating particle size of about 0.3 micrometers at a flow of 85 liters per minute; a P100 must remove 99.97 percent and resist oil. The Chinese GB 2626 KN95 class and the European EN 149 FFP2 class specify 95 and 94 percent respectively. Surgical masks are tested to ASTM F2100 for bacterial and particle filtration of the material itself, but they are not fit-tested and are not respirators. Because leakage bypasses the filter entirely, fit dominates the outcome, which is why this model multiplies rated efficiency by a fit factor. Occupational practice quantifies that directly: under the OSHA respiratory protection rule a half-facepiece respirator must achieve a fit factor of at least 100 on a fit test before it can be relied on. The wear-time term should be read as a rough penalty rather than as physics. Filtration in electret media degrades chiefly through moisture, oils and improper decontamination rather than through hours worn, and in extended-use studies straps, seals and comfort usually fail before filtration does. The broader caveat is that no single multiplication predicts infection risk, which depends on exposure duration, ventilation rate, source control and viral load, as in Wells-Riley style airborne models.

The surgical mask entered practice in 1897, when Johann von Mikulicz-Radecki in Breslau and Paul Berger in Paris independently began covering the nose and mouth in the operating theatre to keep droplets from surgeons out of open wounds. Its first mass public use came during the Manchurian plague of 1910 and 1911, where Wu Lien-teh designed a layered cotton and gauze mask and argued, against much contemporary opinion, that the disease was spreading through the air. Similar masks reappeared across cities during the 1918 influenza pandemic. The disposable filtering facepiece is a much later invention. Sara Little Turnbull's work with 3M on molded non-woven forms during the 1960s led to a molded dust mask in the early 1970s, and the enabling technology was electrostatically charged melt-blown polypropylene, refined through corona-charging methods developed by Peter Tsai at the University of Tennessee in the 1990s, which captures fine particles without the breathing resistance a purely mechanical filter would require. NIOSH created the N, R and P classes with 95, 99 and 100 efficiency tiers when it revised 42 CFR Part 84 in 1995. Mass civilian use followed the SARS outbreak of 2003 and then COVID-19, when agencies recommended community masking in 2020 and large field trials, including a cluster-randomized study across hundreds of Bangladeshi villages reported in 2021 and 2022, measured real-world effects far smaller than bench filtration figures alone would suggest.