Masking for COVID: fit for purpose?

With mixed data on the effectiveness of masks, are people just not wearing them properly?
20 July 2021

Interview with 

Eugenia O'Kelly, University of Cambridge


A woman wearing a facemask.


First they weren't introduced. Then they were mandatory; then, with ‘freedom day’, they weren't, and now, confusingly, in some parts of the country you'll have to go by whatever rules the local councils and businesses are putting in place... for face coverings. So why the controversy, and what's the evidence that these things actually work? Well as engineer Eugenia O'Kelly - who heads up Cambridge University's Respiratory Protection Engineering Task Force - explains, the signs are that they can make a difference, but most people aren't wearing them properly, and that's limiting their effectiveness. So are they “fit” for purpose? Chris Smith found out...

Eugenia - There are two purposes that a face covering can serve. One is to protect others, and the second purpose is to protect yourself. In terms of protecting others, the face-covering will prevent any sort of droplets that you exhale from being distributed around the environment. The second purpose of a mask is to protect yourself. And if you're wearing a mask to protect yourself, the engineering challenges of that are quite a bit higher. You actually want to be filtering all the air that you're inhaling. And for that, you have to have a material that has high enough filtration ability that it's going to be catching a sufficient number of viruses or pollutants. And secondly, and more challengingly, it has to fit well enough that air isn't just going to be leaking around the sides of the mask.

Chris - Is not another problem that when doctors, nurses, other healthcare workers in hospital use close-fitting masks designed to exclude viruses in the body, they're combined with other elements of personal protective equipment, such as aprons, gloves, scrubs, eye protection, the idea being that there are multiple routes into the body via various direct and indirect pathways, and you've got to close off all of them, or it's not worth the additional protection of these very, very stringent masks.

Eugenia - Yes. I would say that if you're really looking for a hundred percent protection, you need additional measures and we're doing a project right now on the amount of droplets that, through normal speaking, end up in the eye area and how different types of glasses that an average person might be wearing may block that. You certainly get quite a few droplets in the eye area when you're normally speaking with someone. And another thing to keep in mind is these healthcare workers, even with just the masks that they have, they have gone through procedures to ensure the masks and the other PPE fit and work. So it's perhaps an unfair standard to expect for your average citizen.

Chris - When people do experiments to work out whether or not masks do arrest a lot of the stuff that's coming through them, do they actually do a comprehensive experiment where they look from behind as well as in front? Because a lot of the studies I've seen have just been looking from the side, looking at stuff being projected forwards. And they're ignoring the fact that I mean, a lot of my colleagues who put face coverings on at work and wear glasses, their glasses are incessantly steaming up. Now that's showing you that there's a lot of material blowing up over the upper part of the face and is not being stopped by a face covering. So how good are your average face coverings at actually stopping these droplets?

Eugenia - I think that's a very good point and one perhaps very good visual of how much escape you can get around the sides of the mask is if you watch someone in a very cold environment, you can see the vapor from your breath escaping around all sides of the mask is significant. And that's really a sign of poor fit. And while those masks are likely to hinder very large droplets that you're projecting when you're speaking, it's not really fitting well enough to filter those smaller particles.

Chris - Do you have a feel for, if you take a person at random off the street who is wearing some kind of face covering, how effectively they are wearing it?

Eugenia - Well, unfortunately at this point we don't have a significant enough sample size that we can really make that assessment. What we have done is we have created a tool so that if you're wearing a higher efficiency mask, such as a surgical mask and FFP2 mask or FFP3 mask, you can at home perform the same type of tests that a hospital performs on its workers to make sure that their masks fit.

Chris - Did you try it on yourself?

Eugenia - Yes, I did. Most of the experiments we've done I've tried on myself while working out some of the kinks.

Chris - And were you masking effectively?

Eugenia - I was not actually. So I tried it on five different masks on myself. And what surprised me was especially given the fact that I've been working with this, reading all of this literature, doing these studies, there were masks I thought fit, and when I tested them, they didn't.


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