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Author Topic: Should we be encouraging mask use where possible even for the legally exempt?  (Read 2384 times)
Bmblbzzz
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« Reply #15 on: October 29, 2020, 04:40:17 pm »

However, in the case of this pandemic it should be quite obvious to everyone why the rules are there. They are there to limit the spread of the virus. So if you have a situation where rule A and rule B appear to be in conflict, the correct thing to do is to look at the reason for the rule and act according to the spirit of the rule, not its letter.
The rules' effectiveness in limiting the spread of the virus is compromised by the need (real or perceived) to keep the economy going and various functions of normal society, such as schools, running. This will lead some people to question the point of following them at all, and others to question the point of the exceptions. That was what I was trying to say, in two sentences.
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Bmblbzzz
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« Reply #16 on: October 29, 2020, 04:43:33 pm »

Incidentally, there's an article here suggesting that the main method of transmission is not droplets but aerosols (the difference being that both are microscopic but droplets are large enough to fall to the ground quickly, aerosols remain airborne). This would mean that indoor settings without ventilation are much more risky than previously thought, regardless of distance from a carrier.

https://english.elpais.com/society/2020-10-28/a-room-a-bar-and-a-class-how-the-coronavirus-is-spread-through-the-air.html
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Marlburian
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« Reply #17 on: October 29, 2020, 05:37:20 pm »

I would rather that we educate and encourage existing users to wear them properly, to take care when adjusting them and to wash them in very hot water frequently  - and to discard them responsibly.
« Last Edit: October 30, 2020, 11:18:25 am by Marlburian » Logged
stuving
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« Reply #18 on: October 29, 2020, 05:58:26 pm »

Incidentally, there's an article here suggesting that the main method of transmission is not droplets but aerosols (the difference being that both are microscopic but droplets are large enough to fall to the ground quickly, aerosols remain airborne). This would mean that indoor settings without ventilation are much more risky than previously thought, regardless of distance from a carrier.

https://english.elpais.com/society/2020-10-28/a-room-a-bar-and-a-class-how-the-coronavirus-is-spread-through-the-air.html

Previously to what? This has been part of the message for months - that's why we've had all the emphasis on ventilation, in trains and elsewhere, not to mention the different rules for meeting  indoors and outdoors. Of course it's been most important in the message for employers and others who control ventilation. The equivalent for homes, schools etc  - open the windows twice an hour to ventilate the room - has been prominent in France, but not here.

And as to "main method" - that depends on where you are and what you are doing. One point is that the fraction of fluid going into aerosol is tiny, so it takes quite a long time to build up an effective dose. In fact, these microscopic droplets are so small that the average number of virus particles in each is well below one.

The bigger droplets fall not just on the floor, but on the person producing them and anything they are close to for a while, building up to heavy contamination. So the size of dose that can be transferred by contact is much bigger - don't dismiss it!  For example, the handle of a shopping trolley is almost the ideal vector, and if someone stands holding onto a grab rail in a train ...
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Red Squirrel
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« Reply #19 on: October 29, 2020, 11:22:44 pm »

...
The bigger droplets fall not just on the floor, but on the person producing them and anything they are close to for a while, building up to heavy contamination. So the size of dose that can be transferred by contact is much bigger - don't dismiss it!  For example, the handle of a shopping trolley is almost the ideal vector, and if someone stands holding onto a grab rail in a train ...

I took this, from the El Pais article, to mean that the risk from touching things was actually very small:

Quote
...contaminated surfaces (fomites), although the US Centers for Disease Control and Prevention (CDC) indicates that this is the least likely way to catch the virus, a conclusion backed by the European Center for Disease Control and Prevention?s (ECDC) observation that not a single case of fomite-caused Covid-19 has been observed...
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Bmblbzzz
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« Reply #20 on: October 30, 2020, 05:21:59 pm »

Back in the spring, it was all about contaminated surfaces. Virtually no one was wearing a mask but there was heavy emphasis on hand washing and surface cleaning. When mask rules came in a few months ago, it was still considered that the main infection method was droplets, with limited distance of spread, hence all the emphasis on keeping a certain distance apart.  Distance seems to be less protection against aerosols, as they don't settle but build up in the atmosphere, but ventilation can reduce their concentration (as it can for droplets to an extent, it seems). Considering aerosols not droplets to be the main vector does seem to be a new approach. But is it correct?
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Bmblbzzz
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« Reply #21 on: October 30, 2020, 05:23:14 pm »

In terms of mask wearing, I'm not sure whether the distinction between aerosols and droplets makes much difference.
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Marlburian
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« Reply #22 on: October 30, 2020, 06:38:33 pm »

Lab tests show there's a massive difference in the effectiveness of the best and worst face masks.

Damn. Last week I bought the  "bottom of the table ... Termin8 lightweight breathable face covering" from Boots and thought it the best of several types I've purchased. Not surprisingly, it appears to be a trade-off between breathability and protection. I find even the Termin8 uncomfortable after a few minutes ' use.
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stuving
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« Reply #23 on: October 30, 2020, 07:15:21 pm »

In terms of mask wearing, I'm not sure whether the distinction between aerosols and droplets makes much difference.

In practice, mask wearing is what requires the distinction. There is of course a size continuum, from raindrop-sized down to smaller than a virus. The bigger the droplet, the faster it falls through air, and "aerosol" is applied to ones that are so small they need to be treated as not falling. That depends on context, like why it matters and how still the air is.

Size matters to masks and filters too, and NHS advice and practice is to use FFP3 respirators only for "aerosol-generating procedures" - they are uncomfortable, need to be fit-tested per person and per use, and almost all have a valve so don't filter outwards. Everyone else wears surgical masks (type R2 fluid or splash resistant), with lower filter effectiveness on aerosol droplets. That distinction is based on size alone, rather than fall rate.

Breathing, talking, and even coughing are not reckoned (or haven't been in the past) to produce enough of these smallest "aerosol" particles to worry about. Pushing a tube down a patient's airway to ventilate them is. It takes mechanical energy to tear water (with or without gloopogens) into smaller droplets, and forced airflow through a small gap does that.

Turning that basis into a public health message has had its problems, too. Some scientists have got het up about the lack of emphasis on airborne transmission, but I reckon it's hard to make that into a simple "do this" message. This is all about behaviour modification, and I also wonder if PHPs (public health professionals) started out fighting the last war - trying to persuade us that respiratory viruses like flu can be passed on by contact unless we keep washing our hands. After all, that's a recent idea - relative to the lifetime of an old wife (or me).
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Bmblbzzz
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« Reply #24 on: October 30, 2020, 08:39:37 pm »

In a healthcare setting, medical professionals choose the appropriate type of mask as you say. But the general public are wearing all sorts of things, often with big holes in or worn under the nose, rendering them ineffective.

Good point about fighting the last war, especially given the amount of talk (mostly in media) about the 1918 flu and the 1968 "Hong Kong flu" (which I'd never heard of before). In 1918 the existence of viruses was still disputed and even in 1968 I wonder how many of the public really knew what they were?
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« Reply #25 on: October 30, 2020, 10:43:18 pm »

In a healthcare setting, medical professionals choose the appropriate type of mask as you say. But the general public are wearing all sorts of things, often with big holes in or worn under the nose, rendering them ineffective.

I don't think I've seen any explanation of what masks are meant to do in the general population. In medical use, based on barrier nursing, taking PPE off and getting rid of it is as important as wearing it. The PPE is just part of a whole process, relying on prepared facilities and training. That's because (in part anyway) it has to deal with high levels of pathogen contamination, and a wide range of pathogens, so the PPE itself becomes a source of infection and has to be handled suitably.

To start with, as the advisors came from that kind of background, they said use by the general public was as likely to do harm as good. But I think there is a case for it just as an extra barrier, to cope with low levels of virus coming from anyone you meet, and the rarer ones who might be quite ill and spreading a lot of it (but you're not very close and not for long). That RSSB study on Covid-19 risk in trains found and adopted a factor of two reduction in infection risk, though they didn't model infection routes separately. I heard a French government figure of a fourfold reduction of the airborne infection risk, which sound broadly consistent with that. That's not a big factor, given how many virions are being produced and how few can infect you.

The other points about masks are that they are not too hard to use for most activities (with some obvious exceptions), and act as a permanent reminder to be good. I'm not sure what the general understanding of what they do is, though.
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ellendune
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« Reply #26 on: October 31, 2020, 08:07:23 am »

I don't think I've seen any explanation of what masks are meant to do in the general population.

I find this a surprising remark.  I have heard many times that the purpose of the general population wearing masks is that it reduces the risk that the wearer will infect other people if they are carrying the virus even if they are asymptomatic.  Or have I missed the point you are making. 

Surely much of the time in barrier nursing the purpose is to protect the wearer. 
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grahame
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« Reply #27 on: October 31, 2020, 12:36:06 pm »

My understanding is that wearing the masks is to protect both the wearer and the person near / around them.   No mask layer between people - 100 "units" of infection risk.  One layer and that risk is slashed, though not symetrically.  Two layer and it's slashed again - perhaps to just 1 or 2 units.  All very much affected by how good the masks are and how properly they are worn.

Now ... I see someone smoking, drinking, cycling without a helmet, etc and I think "it is up to them if they want to take the risk" and I am unlikely to have any desire to say anything or want to police them in any way.  With the masks, so much of the protection when I meet a person without a mask is my protection rather than there's that I am more inclined to challenge, or to take steps to lower the risk to myself by removing myself from them.

On Monday, I volunteered at [xxxxx] and on knocking on the door where that was to take place, I was asked by the boss to put on a mask, and did.  Both people already there were masked.   Correct.

On Tuesday, at the same place, the only the organiser (not the boss) was around, and she was maskless. I was fully masked all the time and felt that she really should have been wearing a mask too, even with the boss not around.

This (Saturday) morning, same place again, and with an early lone start to my shift I had no access.  Contractors turned up with keys during my shift, in multiple cars;  I hadn't expected them and put my head around the door because I know there have been security issues - clearly genuine, but clearly all three people not wearing masks and as they were working in the smallest room, certainly not distancing.  When my replacement arrived - a director of the outfit I'm helping - he was masked; I passed over to him out of doors, and left him to carry on.

So - no challenge from me, but a personal caution that I won't be putting myself indoors there again until I'm reasonably sure that the organiser and anyone else who she has around is following the rules that the boss has rightly implemented. To expect others to wear masks, but not to do so yourself if you can, is both a personal risk and shows a disregard, ignorance, thoughlessness or arrogance for the health and lives of those around you.



I quote a specific incident above, but it is far from unique.  Coming back from Bath on Wednesday evening, chap gets on the bus ... comes upstairs where I am seated, and as he sits down takes his mask off.  "You're supposed to keep that on right through the journey" say I, more especially as he has sat down opposite me, aisle seat, and is asking me about the previous bus and if I know why it didn't turn up.   "Oh - it's OK - I',m exempt" he says ... "Just put it on while I got on the bus and came past the driver".   Not OK as he proceeded to have an extended discussion about buses ...
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Bmblbzzz
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« Reply #28 on: November 03, 2020, 06:04:05 pm »

Out of interest, do people think you should have to wear a mask when riding a bicycle?
Probably not. You'll be in the open air, obviously, and won't be close to anyone for any length of time. The exception would be riding in a group, inna peloton stylee. In that situation it might be sensible. But I don't know if it's really possible to get enough air through a mask for riding hard and the slower you go, the less you're likely to be drafting etc anyway. And the risk would probably be less than, say, a rugby scrum, simply because you're not quite that close. That's my take on it anyway.
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