Uncovering the truth behind the mask
The recent global outbreak of novel Coronavirus has seen a new trend emerge - in cities like Hong Kong, it is a rarity to see someone walking in public without wearing a mask. The masks come in a multitude of colors and styles, but which one offers the best protection against this new virus? More specifically, should you be hunting down a surgical mask, or an N95 type of mask?
Surgical masks are designed for various medical procedures, and as such are subject to grading by the American Society for Testing and Materials (“ASTM”). The ASTM has categorized masks into various levels, depending on the mask’s ability to resist fluids, filter particles, withstand pressure and flames. For the casual mask-wearer who does not intend to engage in activities that produce large amounts of fluid or aerosol spray, the most critical parameter to pay attention to here is the Particulate Filtration Efficiency (“PFE”) at 0.1 micron. ASTM Level 3 and Level 2 masks reach a >98% efficiency, while ASTM Level 1 masks reach a >95% efficiency. This is a relevant benchmark for our current outbreak since coronaviruses are typically around 0.1 micron in size.
On the other hand, N95 masks were originally designed for the construction industry, but have since branched out into the medical field as well. According to 3M’s own press kit, the N95 respirators specifically designed for healthcare uses have a PFE of >95% at 0.3 micron. Just looking at these numbers, doesn’t this mean the N95 is in fact less effective at preventing you from getting the coronavirus? Before we jump to conclusions, it is important to consider one big factor in mask wearing that we have not yet addressed, and that is “user error”.
For a surgical mask to function at its peak performance, it needs to be worn correctly, well-fitted to the face, and not allowing air to seep through the gaps typically formed around the nose, the cheeks, and the chin. In contrast, N95 respirators are designed to fit snugly around the face, and as long as you don’t sport a beard or have an inordinately small face, these tend to leave very limited gaps.
At the end of the day, if you’re planning to be out in public in an enclosed area coming into close contact with people, it’s probably wise to wear some kind of protection over your nose and mouth. If nothing else, it at least stops us from accidentally touching our faces with our dirty hands! But if you’re trying to figure out what kind of mask to buy, hopefully now you have a little more insight on the sheath you’re putting on your face!
https://multimedia.3m.com/mws/media/769925O/3m-disposable-respirators-catalogue.pdf