Author Archives: Richard Sear

Google recommended to me this article in Pulse: a publication for GPs. It made me wince quite a bit. A representative of the UK’s “NHS England national infection prevention and control team” was suggesting GPs and others wear surgical masks. The evidence is that FFP2s would be better, offer more protection. I was particularly struck by:

However, she [a “NHS England national infection prevention and control team member”] added that the UK Health and Safety Executive recommends healthcare professionals ‘should not use’ FFP2 masks and that ‘the only requirement to use them’ would be ‘if you couldn’t get FFP3’.

GPs should not routinely use FFP2 as surgical mask gives ‘very good protection’, Pulse, 19th Jan 2022

That is kind of true, the UK’s Health and Safety Executive says:

HSE’s current stance is that where there is a respiratory risk of infection use of FFP3 devices represents best practice, and where these are not available then FFP2 may be an acceptable, pragmatic compromise.

Evaluating the protection afforded by surgical masks against influenza bioaerosols (Research Report 619), Prepared by the Health and Safety Laboratory for the Health and Safety Executive 2008

So, the HSE (who are people in the UK government who understand masks – unlike apparently NHS infection prevention and control) are indeed advising against FFP2s when there is significant risk of infection. They are advising upgrading to a better mask. FFP3s are better than FFP2s. They are not recommending downgrading to the much worse surgical masks, as NHS national infection prevention and control is doing. Odd.

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Today there was a COVID-19 press conference, with the Prime Minister Boris Johnson, and Sirs Chris Whitty and Patrick Valance. It is on YouTube. At about 38 minutes LBC’s Ben Kentish asked a couple of questions. Sir Chris Whitty gave what sounded to me like an excellent answer on vaccines, clear, authoritative, from the heart, and useful. Impressive. He was also also asked about some healthcare workers not getting FFP3 masks. Maybe the question was a little vague but the answer was certainly vague and he did imply that there was a debate about where an FFP3 was useful and where they are not.

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It may not be obvious that there is a connection between the air-conditioning units of Boeing airliners, and the survival of viruses, but there is. In the 1960s, an engineer called Proschan, while working for Boeing, was studying the failure statistics of the air-conditioning units in airliners. He was a pioneer of what is often called survival analysis – the branch of statistics that deals with failure/death. The same statistics applies both to failure of a machine, or death of an organism — and to the demise of a virus, which is perhaps somewhere between a machine and an organism.

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Many people are wearing surgical masks, even though SARS-CoV-2 is airborne and so a better fitting mask, eg FFP2, would offer a lot more protection. But surgical, and cloth, masks are not useless, if you are infected they are good at stopping you breathing virus-laden particles directly onto to anyone you are talking directly at, and are close to. This is nicely illustrated in a recent work by Bourrianne and coworkers. The basic point is simple, we need to breathe in and out, about once every couple of seconds. When we breathe out we push out a litre or two of air in about a second. This goes through some combination of our nostrils, and a typically mostly closed mouth. This is quite a small area, perhaps a few square centimetres. Basic geometry says that to expel 1 litre through holes say 10 cm² in area, you need a speed of 1 m/s. This is quite fast and results in a cone of air shooting out from your mouth/nose towards anyone you are facing*. The cone rapidly dissipates in the room air but still you are imparting momentum to your breath which carries it and any nasties it may be carrying towards anyone you are facing.

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Above is a plot of prevalence of COVID-19 in children versus the concentration of carbon dioxide (CO2) in their classrooms. Prevalence is defined as being number of children who test positive for COVID-19 per 100, so 0.01 means one in 10,000 children has COVID-19. Cumulative CO2 concentration is obtained by integrating CO2 concentration over something like a school day, I think. The data is from a study by Empa (part of the Swiss university ETH), of classrooms in Graubünden, a canton of Switzerland. As they say, this is very preliminary, but although of course the data is noisy there does seem to be a trend. The R in the plot is Pearson’s correlation coefficient, and a value of 0.72 suggests a significant correlation between the amount of CO2 in the air children are breathing in classrooms, and how many are becoming infected with COVID-19.

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As a 50-year-old guy I find it a bit weird to recommend a YouTube channel, but I am going to recommend Aaron Collins’ YouTube channel on masks*. Back in Spring/Summer 2020 we were (rightly I think) urged to avoid the sophisticated masks used by healthcare workers, because there was a shortage of these masks and these frontline workers needed them more. But now there is no shortage, so we should wear the best mask we can. See Aaron Collins’ channel for him testing masks and recommending the best masks. Not all masks are the same, some offer much more protection than others. The filtration properties of cotton fabric are generally pretty poor (colleagues and I have a preprint on that), but the best masks are made from sophisticated filtration medium which is much much better.

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