UKC

Given that we are moving to a time of year where more and more people will want to socialise indoors, is there a way of making it safe to do so? Obviously, we know masks help a bit, but no good if you want to eat or drink with people. Pubs and restaurants seem pretty risky as the airborne virus particles can build up etc.

If a single door or window is open, does this refresh the air inside the space often enough? Or does it just move the virus around the room more so spread to more people? What about 2 windows so there is an actual flow of air? Does this also just spread it to more people or will it dilute it more to be less of an issue? Is there a way or using aircon or fans to move air away from people without it moving past others?

Or do we just have to accept that this year is an outdoor winter and suck it up? We have a woodburner in our lean-to which makes outdoor dining feasible with a warm jacket. Fine for us and parents but a bit chilly for 89 year old granny. Many will not have a feasible outdoor option, so can the hospitality industry make it work? 

Try it and see. 
 

If I open my back door and front door at the same time, the kitchen door slams. That tells me something. 

It tells me that air moves through the space, but is that replacement of air enough to stop the spread by diluting it, or does it move it in a concentrated way past other people so that it would be a high enough dose to infect them?

I'm not sure you're going to get a definitive answer to that question on a climbing forum.

A question about a sling in a draw, solicited a myriad of answers and some heated debate, and that could in theory be physically tested, at lest up to a point.

I reckoned if I was going to get a good answer anywhere it would be here! There are a lot of very clever people with very diverse specialisms on here. I have often found you get some great answers to all sorts of very random questions on here!

You’re stopping the air from stagnating. You won’t get infected from one breath of air from someone. You will if you stand next to them for 15minutes.

Use smoke as an analogue for virus laden aerols. Think back to pre 2006 pubs or times when it was acceptable to smoke in anotjers home. 

Smoke clears much more readily if there is a through draft. 

Some ideas here.

https://www.nytimes.com/2020/04/20/health/airflow-coronavirus-restaurants.h...

https://news.harvard.edu/gazette/story/2020/06/air-conditioning-may-be-fact...

I'm teaching 'pods' of year 7 classes who stay in the same classroom all day. I make sure that a, the door is open, b, the windows are open and c, I sit/stand as close to the windows as possible so any 'contaminated air' (if there is any from 11 year olds) blows away from me. So, sit by the window with the best incoming draught.

I'm not sure you'll get enough airflow to make a meaningful difference without making things pretty unpleasant; looking at the quantities of airflow we use to suppress particle counts in labs and cleanrooms you aren't talking about just leaving a window open. (We typically run between 20-30 air changes an hour)

I'm struggling to find a decent study to back that assumption up though. 

You MAY if you stand next to them for 15 minutes.

Small but crucial difference...

Get something which generates visible smoke and watch what happens. to it.   It should be clear whether it is being dispersed and diluted.   Whether it is sufficiently diluted is a much harder question. 

https://engineering.stackexchange.com/questions/417/how-to-make-smoke-for-a...

I’m working on the same principle, plus mask if I am within a metre of the kids.  

Windows and doors open and get fresh air in and through as much as possible.  However I expect complaints to increase as the weather gets colder.  

https://www.theguardian.com/world/2020/mar/11/if-you-want-to-fight-infectio...

https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa939/586779...

I don't think there is a simple outdoor equivalent of air changes per hour, but if you multiply air changes per hour by the length of the room you get an estimate for speed of the air in the room.

Say your lab is 30m long, at 30 changes per hour the flow is 0.9kph. Lower if lab smaller or flow not along longest dimension.

I suspect a "windless day" outdoors has more breeze than that. Alternatively light a cigarette in your lab and see how it compares to outdoors! 

https://www.statista.com/statistics/322785/average-wind-speed-in-the-united...

Average wind speed is 8.2knots or 15kph so if your hypothetical 30m long lab was open to the wind it would have 500 air changes per hour for wind along length of lab. More if wind was along a shorter dimension.

Hence my pet theory that outdoors is safe and far quicker dilution that any lab!

At my school, all classrooms have windows and doors to corridors open during classes, presumably on sound advice. I think the idea is that the air in the room gets replaced frequently. Though I reckon we'll have our first hypothermia cases before Christmas.

Clean rooms are slightly different, they’re measured in changes of air per hour - for a good reason. We use about 10 l/s of fresh air per person in office spaces as a minimum, 15l/s is usual and 20l/s is very good. 

This is an interesting and relevant article on airborne transmission: https://www.technologyreview.com/2020/10/02/1009235/this-scientist-made-a-g...

Yes, the authors believe that airborne transmission by aerosols rather than droplets causes most infections.

What can you do about it? Well if you think of how a smoker's cigarette smoke wafts around indoors and out I guess that's a reasonable analogy. Opening a window is going to help unless you sit next to it. Being outside will definitely help as the exhaled air can go up as well as sideways. Exactly how exhalations move around any particular room must depend upon its shape and the airflow round it.

I think the article also notes that it does take a certain amount of time for there to be a high probability of getting infected so I suppose moving every five minutes might help.

It’s people’s front rooms. The infections have stalled in the North West where they stopped people visiting each other’s houses. Which also makes a good case for reducing pub opening hours. 

So it looks like what we are saying is that winter weather is going to stop indoor premises from getting sufficient airflow due to people not tolerating the cold? One window on its own is unlikely to be enough, I guess. I presume retro fitting a suitable ventilation/ air filtration system is going to be super expensive so really not possible. 

Not such a problem if people are wearing masks (shops etc) but restaurants, pubs, gyms etc are all looking risky. 

I had wondered if I would be willing to break my no indoor rule if I could find somewhere suitable so we could eat out with Granny when it gets too cold for our lean-to, but sounds like it won't be an option. Just have to choose the milder days and sit her closest to the stove with plenty of blankets.

I'm going to be telling my students to wear warm clothing and extra layers.  I've gone back to work despite my reservations, but I'm not spending extended periods in any room without the windows and door open.  

I'd have said so, yes.

We are approaching some interesting times. 

What happens to minimum working temperatures with an icy blast maintaining ventilation?

How are reasonable indoor temps maintained whilst achieving energy use targets and lowering carbon emissions in a highly ventilated environment? 

Short term this will be tolerable, less so long term. 

I'm not sure how it will work, beyond what I did last winter (nothing to do with Covid and everything to do with the state of some of our school buildings) which is keep a thermometer on my desk to wave in the face of any management types that wander in demanding to know why the children haven't taken their coats off, and get as many portable electric heaters going as possible, whilst trying to prevent the children from meddling with them and putting their bags on them etc.  Bonus points for actually teaching some maths while all this is going on.  

Personally I'm good, I don't mind the cold.  My tolerance from a childhood with no central heating and snow on the inside of windows seems to have stuck along with the knowledge from camping of how to dress in layers to keep warm.  

There are no legal minimum working temperatures. 
 

It’s only a few weeks that it’ll be bad. 
 

Get up regularly and walk around. I suspect anyone who can’t actually work from home will be doing a reasonable physical job that requires their physical presence. 

I can't have 30 kids walk around a small room.  

A quick sprint around the playground? 

A good approach to treatment of calves with pneumonia, is to change the management, and improve the airflow in the calf house, by opening most of the windows;no matter what time of year it is. It works by reducing the concentration of infectious agents in the air, and thereby reduces the challenge for each individual. So your ideas are sensible and in parallel.

How you do it is difficult: And as has been said above, how do you justify opening windows, and then address the environmental worries about reducing the energy requirements for keeping a building heated. (Meantime, my house is mostly colder inside than outside, for much of the year; which is fine in summer.....).

Nice idea, but I don't think I'd be allowed.  

It should be mandated!

Not much to add that others haven't already said.

There are a number of buildings at my workplace with very high capacity air conditioning and / or filtration systems, all of which make a fair, but manageable, amount of noise. Opening two doors simultaneously doesn't appear to make much difference to the air monitoring systems in terms of particulate measured.

Step outside and take measurements with the same equipment and you'll get negligible results. Only an instrument with a very large surface area would work. Granted this tends to be with solid particles rather than aerosols or liquid droplets.

In your situation I would suggest any enclosed space regardless of how many windows you have open will have a much higher risk of the same air hanging around compared to outdoors. 

I suspect a big through draft is better than a closed box. A big up or down draft extraction system would make for a pretty safe space but since this is hopefully a time limited problem I don't imagine many venues will do it. 

No proof. Like you I wonder about a through draft causing spread. 

Jk

Fixed it for you. 

My lefty cynicism sees an opportunity for government to quietly do away with such protections to workers health and safety under the guise of covid, only for them never to return. 

The schools in Germany are going for installing CO2 meters as they give an (indirect) indication of the potential viral load and how effective the ventilation is. If the classrooms can't be ventilated enough then air purifying or ventilation systems  will be fitted (at least in Bavaria).

Strong draughts are to be avoided as they cause droplets to form aerosols.

There is neither a minimum nor maximum working temperature set in the UK, just "reasonable".

Letters have been sent to parents in our local authority saying exactly that.

I suspect that those saying the cold won't be a real issue are revealing their locations (south!) and a lack of experience with kids in the cold.

Those next to the windows in my room have already experienced single figure temperatures this week and we can expect similar or worse at lots of points in the next 6 months.

Extra clothing will help up to a point but some people are just really badly affected by the cold.

Plus we have air recirculation heating and have been told not to use it for fears that it will also recirculate virus laden droplets.

HASAWA guidance is 16 C for sedentary work, 13 C for physical work. There is no upper limit. 

Whilst not a limit such as a speed limit, the guidance gives a workable value. 

When I was a T U rep in education, on cold days I would liase with the head on the understanding that if temps remained below 16 for more than an hour I would be requesting additional heating or asking for the children to be sent home. This was a common strategy both locally and nationally. 

Guidance and suggested.

It used to be 18 for classrooms but it was quietly abolished.  

I've also been told I can't just move those who feel the cold away from the window, as despite the bubble they are on a covid seating plan.  I'm not clear that this is anything but window dressing.  

Yes, we've had to submit seating plans to help with contact tracing so moving people could be an issue.

It's a really difficult situation compounded by the total lack of cash and weak leadership in our local authority.

Badum tish.  

Makes sense.  I've had CO2 meters in classrooms before and to keep them green needed the windows open or the fan on.  

I think they are a good idea.  

It was a happy accident. 

But even if someone came up with figure of air flow of 23 cubic meters per hour, how would you measure that?

I know we're good but....

Natural ventilation is a extremely effective way to ensure good air flow in a building, all you need is a big opening and a small vent to ensure pressurisation and a good air flow, so a window fully open at one side of room or building and a window slightly open at opposite side.  I imagine for office and many work spaces good natural ventilation will be as effective or more effective than social distancing or mask wearing alone in reducing Infection spread.  

I am sure with more people working from home, less people driving, less people flying we don't need to worry to much about environmental cost of this for just one winter, can't imagine increase energy use this year will make any difference to levels of climate change experienced in 2100.

No matter how cold it gets I will always ensure windows open in my work space and expect the people I manage to stick more clothes on if they are complaining about the cold.

I have seen various reports regarding benefits of indoor ventilation, and in terms of health and safety at work act seems an no brainer in being used to keep people safe at work.

As I wrote, there is no law.

Anemometers at the widows. 
 

We do it all the time when we balance the airflow from ventilation in a building. 
 

Widows are going to be quite difficult to do as you’d have to average the sensor (over 10minutes I would have thought?). Wind doesn’t behave very well compared with fans controlled by microprocessors to maintain a constant flow. 

That’s interesting. What level ppm did they stop being green? 

No idea sorry.  I know nothing about them other than they were in the classroom and they definitely responded well to the windows being opened.  

I've googled and it seems they are adjustable.  

This isn't the one I had but it gives an idea of the ranges.

https://www.flamefast-gas-safety.co.uk/co2-temp-monitor-co2m.html

There is a table if you scroll down..

Ah, specific advice

I'm led to believe that's the limits we are using as well.

Maybe I will get myself a portable CO2 detector.  

Cool. 
 

We try and control Auditoriums to 800ppm. 400ppm is normal background. We ramp up fans as the CO2 increases, stops people falling asleep. Well, it reduces the chances, we can’t control who is lecturing. 

You think she has anemometers?

We do to, but we have the equipment.

that was my point.

Besides no one knowning what the limit is for covid safety, so it's all a bit difficult for anyone to give a figure for someone's house using the breeze to do it.

Ok. I didn’t take ‘you’ to mean specifically girlymonkey I took it to be more general. 
 

You can get a cheap anemometer for less than £20. They use them for kitesurfing etc. 
 

A quick calculation with the window cross sectional area, work out the volume of the room, decide minimum changes per hour, which would give you a minimum airspeed and you’re good to go. Evacuate Granny to a safe area if the wind is less than determined DefCon2 levels. 
 

Cross ventilation is an effective tool to create airflow through a building. Architects often use it to try to get rid of excess heat in airtight buildings.

There is a tool to calculate it on PHPP - the Passivhaus Planning Package. If you knew the details of the building you could get typical figure which might be what you're looking for.

If you had a mechanical ventilation system there could be an argument for increasing the ventilation if you thought there was a risk of someone in your house having corona. In practice, i would just limit your family group to your house.

Thats the crux of it really, as a general rule increasing ventilation will remove droplets containing covid from the immediate area more  rapidly than in still air, (although it's possible that droplets that would drop by gravity before they entered another persons breathing zone could be carried by airflow into that persons breathing zone..)

Beyond that it's pointless to start buying anemometers, calculating volumetric airflow and room volumes, working out the viscosity and median aerodynamic diameter and viral loads of covid containing droplets, amount of droplets exhaled based on number of guests,  determining an average airborne concentration of covid based on those factors, breating rates of occupants to work out amount of covid inhaled...you could even factor in the number of people wearing synthetic fleeces, get them to rub them vigourously and claim a bit of electrostatic precipitiation.

As you say, any number you come up with will be pretty meaningless. Outdoor has been assessed as 'safer' than indoor, so as much airflow as possible and if an open window is effectively the room 'extract' then maybe don't sit in front of it is as probably as good as it gets.

What I can tell people is that I've found the CO2 readouts for my classrooms today.  

With all the windows and door open it's been quite easy to get around 550 ppm Its quite breezy today which helps.

Having the blinds shut (its actually sunny) made it difficult to get below 650 ish.

I've just been in the classroom I will be in after lunch.  With the windows and door closed it was about 1100. I will report back later.  

I've opened everything and gone outside.  I've told the pupils I won't teach them with the windows shut and they need to dress accordingly.  

the "you" was directed at girlmonkey, not a general "you"

I'm aware of this

What's a safe levels of virus, and how much air flow do you need to achieve this?

If more than one person has the virus but are a different stages, what then becomes the safe level?

etc., etc., etc.

Is the draft caused by opening the windows and doors constant enough to ensure the calculations above are exceeded? blah blah blah.

This would seem to be a useful read:-

https://www.theguardian.com/world/2020/sep/30/germans-embrace-fresh-air-to-...

So when I returned to the room it was around 450ppm. There were half as many pupils as normal and it stayed low.  

It appears to me that ventilation by opening windows and doors can make quite a big decrease in risk. 

It seems to me that by opening windows before lunch I reduced the risk by a factor of almost 15.  

(1200 -450) / (450 - 50) 

I think CO2 can be considered directly related to used air rather than fresh air.  Any thoughts on that? 

I don't think that is going to be quite so dramatic except when there are large numbers of people in a confined space.  

However it seems very much worth opening the windows and door.  

CO2 is a gas though, heavier than air, it would depend on where your CO2 monitor was situated. CO2 will not lay on a flat surface above ground level and would be easier to disperse from a room, I'd imagine.

We STILL don't know for sure, though if covid is caught from airborne particles or from touch, or more to the point if it's both, most likely, but in what proportions? These are all still theories and conjecture.

Can the virus still be active on hard surfaces for 72 hours as we were first told?

I would agree, like wearing a mask, it's not going to make things worse.

My point, if I had one, was there's no way anyone can answer the question posed in the OP, without a massive amount of additional knowledge and measuring systems in place.

And relying on natural ventilation is even more variable, than an office.

I'm going to be a bit pedantic here, you reduced the concentration of CO2 from 1200 to 450ppm. Depending on where the detector is and how well calibrated you've maybe dropped the concentration by about 60%. Even if it did the same with Covid virus concentration, how much that would reduce the risk of contacting Covid isn't really quantifiable, other than it may well be lower.

As Cobra Head has said, you can't really equate a gas with a liquid aerosol of varying particle size, which is how Covid seems to propagate. As he also said, it's likely to drop onto desks quite rapidly. If there's a lot of airflow over the desk could it resuspend in the air as smaller, more easily inhaled droplets? I dunno, probably not but Has anyone done the experimentation?

Absolutely, which seems to match the current advice.

and me. You could theoretically have a large building such as a school or office block in a breezy location where the low-pressure areas act as an exhaust for the rest of the building and thus people in those rooms will be receiving 'dirty' air from everywhere else.  I can see some places opting for fan-powered positive pressure ventilation to take air in through one place and force it out through all the workspaces to prevent one workspace infecting another.

Excess CO2 due to occupancy reduced from 800ppm (1200-400) to 50ppm (450-400). Occupants have not stopped breathing so CO2 production unchanged but dilution 16 times quicker?

Heavier particles avoided by 2m distancing. Lighter particles reduced in concentration by rapid dilution in same way as CO2.

Nothing proven, although there are very few clusters of infection outdoors reported.

And surfaces?

Doh! Good point, be odd if it dropped below normal atmospheric levels!

Intuitively that seems correct, although for heavier particles increased airflow would mean they'd be carried further before they dropped low enough to avoid being inhaled. That might increase the risk of larger, more viral loaded particles crossing the 2m gap and being inhaled. It would be an interesting bit of modelling

I think that's the key thing.

How would we know, surely you need some sort of test and trace system working to find this data?

Yes, if only we had a functional test and trace....

In other countries that have effective test and trace there are few or no instances of outdoor infection clusters reported. I have not read much of the literature but the report below has some outdoor clusters (building sites in Singapore). Loads more indoors.

https://wellcomeopenresearch.org/articles/5-83

Oh bugger! That makes sense!

Same* amount of Covid exhaled diluted by more air passing through room so amount inhaled much less. 

*unless the cold draught makes them cough!

Track and trace suggests this happens but possibly not very important. Eg office building transmission was based on seating (proximity and long duration) and those on other floors who shared lifts (short duration) and used the same lift buttons were not infected.

You’d have to have put your hands on something that was highly contaminated and then put your hands in your mouth before you’d washed them. The 72 hours experiments were done with high levels of virus to determine how long they could be detected for. 

Agreed, but what constitutes highly contaminated, a simply sneezeful, more or less? Half a sneezeful?

72 hours is a very long time though, especially compared to someone having a party in their house with the windows opened.

Something that's quit hard to judge with a £20 anemometer, I'm sure.

No documented cases of fomite transmission, all cases have also included contact with an infected person. 

That's not the same as saying it can't or hasn't happened.

We also seem to be spending a lot of time, money and effort, using gels and sanitisers, and washing our hands more regularly, considering how little we touch others .

Are we wasting our time?

No, because if you have the virus and aren’t washing your hands they become more and more contaminated as the day goes on. 
 

I’d suggest that most people are washing hands. 
 

So likelihoods go something like. 
Someone has to have the virus and be wandering around. Most people will be self isolating so numbers are reduced compared to actual cases. They have to be not washing hands. They have to touch something and deposit a decent amount of virus that can survive until the next person comes along. They must pick up enough virus to be an infectious dose, they must then transfer enough of that virus from their hands to their eyes/mouth before next washing their hands. 
 

An R of 3 at the height of the pandemic in the U.K. suggests to me that this is a highly unlikely scenario. R would have been much higher. Even as it is it seems quite difficult to catch for a lot of people. 

But so what, if you can't catch it from surfaces, then the only way you could pass it on would be to put your finger / hands in someone else's gob. or other orifice, if you can catch covid that way.

Me too.

This make no sense at all, most people are asymptomatic, so won't know they have it so won't be self isolating.

Who said you can’t catch it from surfaces. 
 

There have been no documented cases. Which means you’re highly unlikely to catch it from surfaces. The people who have caught it have been explained by other means. 
 

They have demonstrated that virus can survive for up to 72 hours and remain viable. as far as I know they haven’t said how much virus they started with and how much they ended up with and whether that’s enough to infect someone. In fact no one has carried out an experiment on human beings to see how much virus they need to infect them. For some fairly obvious ethical reasons. 
 

Are they? 

I'm not convinced, how could they tell if you picked it up from a surface or breathed in some droplets. They simply know you have the disease, and where you caught if from, not how (at least in a lot of cases).

Again, if you can't catch if from surfaces why bother with sanitiser or hand washing, simply don't breathe anyone else's effluvia and you'll be fine.

out of 700+ people testing positive at one of the universities, less than 15 had symptoms.