WINDOWS! Hands, Face, Space
We're in a respiratory pandemic, with an airborne pathogen, mostly spread by breathing in someone-else's exhaled air. Shops, Hospitality, Transport (and others), open your damn windows!
By keeping all the windows and doors open, we can replace the inside air with fresh air, multiple times an hour. Eliminating second-hand "shared air" makes us all safer: if you could smell someone's cigarette smoke, you could be inhaling their viruses.
Maximise ventilation as well as wearing masks indoors, 2m+ distancing, and other measures.
We can think about coronavirus-transmission if it were passive smoking (but far more deadly). We already know how to visualise this (we have a good mental picture of the way smoke moves) and understand how to mitigate it (distance, fresh air).
But too many people misunderstand how the virus spreads, and so they do what they think is most obvious. Poor public-health information, which omits this factor, makes most people focus primarily on frequent hand and surface sanitisation. Sanitisation is a good idea,
but it is not as important as ventilation.
Opening windows and doors is also simple, and low-cost - we can just keep our coats on inside. This virus is highly transmissible (even more so in the new variants), and severe enough to crush the economy: so no excuses!
Maximise ventilation. All shops, supermarkets, restaurants, cafes, workplaces, buses, trains, taxis, care-homes (especially with visitors), pubs, theatres, gyms, hairdressers, (and houses with indoor visitors): KEEP ALL DOORS AND WINDOWS WIDE OPEN.
- Aim for full fresh-air replacement at least 3x per hour. (This is routine in schools in Germany).
- Most air-conditioning or heating systems don't help at all, and they can filter dust, but not viruses; they may often make it worse by re-circulating and spreading the air.
- We can wear coats, sweaters, hats indoors when needed, or use radiant heaters to stay warm.
It should be windy indoors. Open side/back/loading-bay doors to promote a through-breeze.
- If your paper flutters around on a desk, you're getting it right. If you can light a candle indoors and the flame doesn't go out, you're getting it wrong.
- It should be too-cold inside. If the heating can cope in winter, then the ventilation is inadequate. more
Normal, well-designed heating systems, can typically warm a house/business/restaurant up from "cold" in about 2-3 hours. So, if you're replacing the air often enough, then this must overwhelm the heating system. If your heating, even on full-blast, can
make you comfortable in winter without gloves/hat/coat, then you don't have good enough ventilation.
- Customers should be wearing their coat, hat, and gloves when they shop, or dine. This is a small inconvenience to bear, if it allows hospitality and retail to remain open more safely. We're British: we can cope with the cold! more
The "no-mask" exemption for eating is not because it's safe, but because it's impossible to eat/drink with a mask on. This means that people on your table, or nearby tables (not just within 2m), are exposed to your pathogens, especially if you are talking.
This is why the higher-tier restrictions say you can only dine out with your current household.
So, for cafes, bars, pubs, restaurants, it's even more essential that you should maximise airflow.
A quick check: many restaurants place a tea-light candle on the table
for ambiance. If you light the candle, and the breeze (outside air, not the HVAC) blows it out, you probably have enough replacement airflow.
Open windows wide on public transport (especially when crowded). If there are no windows... make some!
- The new trains (and certain minivan taxis) that don't have properly opening windows, must be "modified" by removing panels entirely if needed. Trains with closed windows are inexcusable, a year into the pandemic.
Air-conditioning and heating systems don't filter out aerosols and viruses. more
Older UK trains were equipped with sliding or folding windows. These were excellent: it was possible to make the carriage windy inside with them all open at speed! The modern ones have no way to open the windows, and rely on the
climate-control system. Even when the climate-control functions correctly (which, on UK trains is not always the case), it does not clean or replace the air with the necessary frequency. HEPA ("high efficiency particulate air") filters
help, a little.
[Aside: aeroplanes with modern systems do have excellent cabin air quality
Wherever possible, move service outside. Reduce density by extending operating-hours.
- Note: this is needed, in addition to wearings masks indoors, though it's especially important when customers are dining in restaurants/pubs/cafes.
- Note: the point of opening windows is to avoid being exposed to somone else's air. You don't need to be cold when you're in your own home with just your own family/bubble. more
However, in a shared household where some people are exposed to different risks, there is an advantage to changing the air
- Tip: Radiant heaters (with glowing elements) can help keep you warm, even when the air is cold. more
To stay warm even when the air is cold, you can use electric radiant heating - these are the type of heater which has a hot glowing element, where the infra-red heat shines on you from a couple of meters away.
[The heater commonly called a "radiator" actually works by convection, heating the air, and obviously if we're blowing the air away, there's no use in heating it.]
A way to keep fingers warm when typing is to use a small desk-lamp fitted with a filament bulb ("GLS" or "Rough service" or "Halogen") placed close by; LED/CFL bulbs won't work for this.
Explanation: see for yourself
We know how much safer it is when air is not recycled - this is precisely why Flu (and Covid-19) peak in the cold season, when everyone crowds indoors and tries to save heat by avoiding draughts. This is not the moment for energy-efficiency.
Outdoor events are generally safe (e.g. there was no spike in cases caused by the black-lives-matter protests).
Droplets: Take a perfume or aftershave mister, hold it in front of your face (pointing away), and spray it. You'll see tiny droplets.
- Droplets have a short-ish range (1-3m), and fall out of the air in under a minute.
- Droplets account for the majority of transmission: that's why we have the "2m rule", and the need to wear masks to protect others.
- Remember the old saying: "coughs and sneezes spread diseases"; but for covid, so does normal breathing and speaking!
Aerosols: Now, fry some onions or garlic. With the doors and windows closed, where else in your house can you smell it? Or observe how you can smell aftershave/perfume on another person from a distance.
- This is an aerosol - the particles travel a long way over a long time, and the particles persist in the air.
- Aerosols account for a significant amount (perhaps 1/3) of transmission. It's why you have to worry about the trail where an infected person has been, not just where they are now, e.g. did they cross your path in the supermarket a minute ago, or
get out of an elevator before you got in?
- Originally (in March 2020) this was not widely known: it's why short social-distancing was considered sufficient. Now we do know, we must replace indoor air frequently.
Outdoors: Repeat the experiments outdoors. Can you smell the perfume or the onions?
- Even the slightest breeze will almost completely remove both droplets and aerosols, or reduce your exposure by a thousandfold.
- Almost all activity outdoors is much much lower-risk than indoors (provided people are not breathing directly on each other, e.g. at an outdoor party, or during a rugby scrum).
Exposure is based on proximity × time. For example, two people spending a morning at opposite ends of an unventilated 10m long room are far more exposed to each other than passing briefly in the hallway.
The transmission numbers are scary right now: ventilation is vital, in addition to masks indoors and vaccination as soon as possible.
We can't see viruses, so how should we imagine them? Think of them like passive smoking, just far more toxic. The virus particles are tiny: they float around with the air, like smoke; they do not move like projectiles, such as raindrops or tennis balls.
shows how the virus moves.
Covid-19 itself is about 0.1 μm
in size. In comparison, dust is about 5 μm; cigarette smoke is about 0.1 μm; droplets are around 100 μm.
1 μm = 1 micron = 0.001 mm.
Droplets do fall out of the air quite fast; aerosols do not
We already know how to protect against passive smoking: for Covid-19, exactly the same approach works, and you should imagine it in the same way. Imagine that 1 person in 50 is smoking, but you can't actually see the smoke, and that just "one breath"
smoke covid can get you infected.
(whereas second hand smoke takes more exposure, over longer-term to harm you.)
You are most likely to breathe in that smoke if you are close to them for several minutes, but smoke moves around inside, and persists long after the smoker has left the room.
- Standing right next to somone who smokes means you breathe in their
smoke covid. The closer you are, the worse this is.
- Driving in a car with a smoker means you breathe in their
- Being in a room with a smoker, even several meters away, even with air-conditioning, means that you breathe in their
- When you walk through the area where someone else was, even 15 minutes later, you can still smell, and be exposed to,
- If you get into a lift that somone else was recently in, you will inhale some of their their exhaled
- If you follow 2m behind someone who smokes, you are still exposed to some of their
- Tobacco smoke can linger on surfaces (that's why a hotel-room that had a smoker will always smell bad, even after weeks and a deep clean). You can pick up some
smoke covid-contamination from surfaces. Covid survives on surfaces for ~hours, depending on the surface material.
- Opening the doors and windows wide lets fresh air in, replaces the
smoke covid contaminated air.
- If you are standing outside and 2m from a smoker, you are much less likely to inhale their
- Be outside: wherever possible, move interactions into the open air.
- Ventilation: replace the air which may be contaminated by droplets and long-lived aerosols.
- Masks: reduce the amount of droplets you breathe out, by trapping them in the fabric. If you are infectious, this helps reduce (but not completely eliminate) the amount you transmit.
- Distancing: 2m reduces your chance of droplet-inhalation; time-separation also matters. This is necessary, but not sufficient.
- Sanitisation: especially commonly/frequently touched surfaces, and hands after touching common surfaces/objects.
If you could smell someone's cigarettes/perfume/aftershave, you are exposed to them!
You can't socially-distance from an "infected ghost" (i.e. the trail where somone was, minutes earlier)
But you can replace their air to reduce your exposure.
Links and References
Here are some links to more information:
- We Need to Talk About Ventilation
"How is it that six months into a respiratory pandemic, we are still doing so little to mitigate airborne transmission?"
- The Atlantic (30 July 2020)
- A room, a bar and a classroom: how the coronavirus is spread through the air
"The risk of contagion is highest in indoor spaces but can be reduced by applying all available measures to combat infection via aerosols. Here is an overview of the likelihood of infection in three everyday scenarios, based on the safety measures used and the length of exposure."
- El País (28 Oct 2020)
- Why Germany is opening windows to reduce Covid-19 outbreaks
"As more people will spend time indoors over winter, the German government wants to ventilate rooms to combat the coronavirus pandemic."
- iNews (19 Oct 2020)
- Think of coronavirus in bars like cigarette smoke, says expert on importance of ventilation
"Everyone knows that if you have some cigarette smoke in an enclosed room even of a decent size you will still smell the tobacco smoke, and it’s the same with the virus, so issues of ventilation are extremely important."
- Euronews (13 Oct 2020)
- Could fresh air help ward off coronavirus infections?
"Epidemiologists say the risk of transmission is much lower in open spaces, and warn of a new outbreak in autumn, when people are likely to spend more time indoors."
- El País (29 May 2020)
- Coronavirus: Fresh air 'forgotten weapon' in fight
"For one GP, the very thought of people keeping windows tight shut 'makes his head explode with anger'. And a leading engineer says he embarrasses his family in restaurants 'by going around trying to bring in fresh air'."
- BBC (24th Dec 2020)
- Fresh Air - Reducing the risk of SARS-CoV-2 spread
"SARS-CoV-2 (coronavirus) is a virus - it travels and can aggregate in the air. Rarely do people become infected outdoors in the fresh air. Plentiful fresh air is more important than only washing hands."
- Dr Eilir Hughes' site, Freshair Wales has been saying this for some time, and expresses it better than we can. More people need to know.
- Dr Eilir Hughes on Twitter
Creator of Freshair Wales and "Hands Face Space Replace". California calls this "Don't Share your Air".
- Dr Eilir Hughes on Twitter, and #HandsFaceSpaceReplace.
- Dr John Campbell (YouTube)
Daily updates, explanations, and information on the pandemic. These videos explan what we should do and why, and how the situation is evolving.
- YouTube (updated daily).
Misunderstandings and Errors
Here are some other things that people are doing wrong....
- Taking the "2m distance" too literally. Other people are not wearing a rotating flail on their head, nor are you in/out-of sword-range. 1.9m = deadly; 2.1m = safe? No, it's not like this! Especially with aerosols: which travel over distance and
persist over time. more
The risk of exposure increases as you get closer, so close contact ("15 minutes at less than 2m") is very high probability of transmission. However, while 3m+ indoors is lower risk, it is not "safe". Also, people leave "trails".
- Not wearing a mask indoors. Masks indoors are highly effective, providing significant protection for others if you are an asymptomatic carrier. (obviously, if you had symptoms, and you knew you might be infected, you'd be isolating anyway). Masks also partially protect the wearer.
In non-crowded outdoor areas, masks are not necessary.
- Wearing the mask wrong. It has to go over the mouth and nose, so your exhaled air goes through the cloth. Otherwise, you're doing it wrong.
Fabric masks are often more comfortable than paper ones.
- Using clear plastic face "shields" instead of masks. Perspex full-face shields that stand away from the face are worthless.
Do not use them: the air flows down and under them without being filtered.
Note: a face shield is sometimes useful in addition to a mask, to protect the wearer in some cases, e.g. a dentist exposed to splatter.
- Perspex partial-face "visors". These products
are really really bad: I have even complained to Amazon to get them widthdrawn from sale. They are particularly hazardous because, not only are they
totally worthless for protection, but not everyone is aware of this, which leads people to get too close. These are also used as a way to "satisfy the rules" on face-coverings. more
A certain restaurant in Mayfair was very proud of how it could use these (awful) products as a way to make their staff seem more welcoming - because it let their waiters smile at their guests. It's true: they do look almost natural, and seem a lot
more inviting and friendly - and the restaurant was welcoming (and very taken aback when I asked the waiter to not lean over and expound at length about the beautifully-presented food). They were trying to do the right thing and didn't know better;
the manager has been referred to this site.
- Misuse of plastic screens. For example, between chairs at a hair-salon, or between tables at a restaurant, when they only block direct line-of-sight. Seriously: who ever came up with these deserves a Nobel prize for fluid-dynamics for discovering entirely new
physics of airflow! We know that air flows around obstacles. Examples: bad,
good (the screen almost completely blocks the teller from the customer). more
The way that many venues use thin perspex screens and shields (following government guidelines!), is as if air somehow didn't flow around them. Magical thinking will not stop this virus; we all know how airflow carries the
scent of perfume, but we're acting as if the virus behaves in accordance with regulations, rather than reality!
- Non wedged-open doors. Especially when selling food, and if they can't even be kicked-open both ways. more
Pret a Manger (as of November/December 2020) are terrible culprits here - their doors swing shut one way, they refuse to wedge them (despite complaints), and
of course, everyone touches the same handle, just before they eat a sandwich with their bare hands! And they removed the napkin stand (for ostensible safety), so we can't even grab a convenient
clean napkin to handle the handle by. If you won't wedge the door, at least make it easy for us to kick it open! Please stop trying to maintain a "comfortable indoor temperature"... we can
keep a coat on! And the point of occupancy-limits is not a "magic number", but to minimise shared exposure to the same "exhaled air/droplets", which, in a closed building, can last for many hours.
- Prioritising "surfaces". Surface transmission was originally thought to be a major factor. In fact, it's the least likely way you can catch it. more
Yes, the virus survive on some surfaces (notably stainless steel) for a while, in ideal conditions. But most of the studies were looking at "detectable traces" of virus, not viable "live" virus. Here are
: "There is still no evidence in any COVID-19 studies that anyone has contracted the virus from a surface alone.".
By all means, clean surfaces, but focus on minimising airborne
transmission first and foremost.
- Sanitising the wrong things. This is harmful when it displaces the important ones. more
I recently observed one very diligent store employee repeatedly sanitising the most obvious surfaces. She was doing what she thought was right, but she didn't know why, so she was sterilising the walls!
Needless to say, this only helps if you have two customers who lick the same wall on the same day. But the employee never cleaned the chip-and-pin machine, nor the door handle, and there was no ventilation either. Good explanations matter in public-health.
- Deep cleans at end-of-day. This is another form of misdirection: the virus can infect someone within minutes, but overnight, it will usually die on its own. more
For example, Transport for London (a major ventilation-culprit!) make a big deal of how they "sanitise their buses every night with anti-viral disinfectant". So, they aren't stopping the virus from being passed on between successive passengers, but they
do prevent the first person to sit down the next day from getting it through their posterior? Besides which, viruses can't survive long (a few hours) outside their host (unlike bacteria which can last much longer), so the disinfection is unnecessary as well as ineffective.
A particularly idiotic extension of this is the "burst-week" system perpetuated by a certain prestigious Art College, which operates its facilities alternate weeks: first opening for a week at slightly-reduced-capacity; then a total shut-down for a week-long clean.
- Failing to think or understand. Viruses are not caused by demons; this is not magic, it's science. Risks can be evaluated and weighed. We can beat this, but everyone needs to know what to do, why they are doing it, and how to deploy their
effort on the most effective countermeasures. Everyone has their part to play: do the things that make the most difference. more
Here's an example of bad risk-management. A while ago, I observed somone very carefully removing disposable gloves, turning them inside out, after using a cashpoint. This was a sensible measure, perhaps avoiding a 1 in 100,000 risk. However, due to the focus on
this, the person walked straight out into the road without looking, incurring a 1 in 100 risk of being flattened by a car. We have to use our brains here!
Tier 5, then what?
Our current strategy is not working. The newest strain is more transmissible and harder to contain, even by the strictest lockdown measures we had in the springtime.
We have to do everything possible, so why isn't maximising ventilation part of that strategy?
- During the strictest lockdown in April-Mar 2020, we got R down to 0.5 - 0.7.
- The new variant increases R by about 0.7.
- This means that full lockdown (worse than Tier 4), combined with the new variant, would still have R significantly above 1.
- The current measurements in London (Tier 4, Dec 23rd) show exactly this: R is between 1.2 - 1.5, with infections growing at 4% - 8% per day.
exponential growth is scary; 8% growth per day means 10.8× increase per month.
The above numbers illustrate the problem we face; the same logic applies everywhere, worldwide. more
The unfortunate truth is this: we applied selective pressure on the virus to make it evolve to be more transmissible. The maths means that it's going to grow and keep growing,
and even the strictest lockdown measures cannot control the virus sufficiently. While we race for the vaccine (and hope for springtime), we need to do better than we are.
Maximum fresh-airflow is the only additional public health policy, which we are not yet doing, which could make a significant impact.
Q: What if we'd be a bit chilly?
A: Dress warmly. (And reassure your customers that the cold is evidence of reduced exposure).
Q: What if your building or train is designed with non-opening windows?
A: Screwdriver/Sledgehammer. (Seriously, we've had 9 months to get this fixed.)
Q: What if your supermarket has auto-closing doors to save energy?
A: Turn off the power, and wedge open. Turn down the heating to avoid wasting it.
Q: What if you can't guard all the doors to your shop?
A: Open them anyway: the risk of theft is small, compared to the risk of bankruptcy from remaining closed if you're stuck in Tier 5 till June.
Open your damn windows!
Come on everyone... Don't make me say it again! If you run a:
bus, train, taxi, restaurant, shop, supermarket, cafe, pub, hairdresser, school, care-home, pharmacy, gym, ...
then you have to help with the fight against Covid-19. There are many things you need to do, but at the very least:
KEEP . ALL . THE . DOORS . AND . WINDOWS . OPEN !!
This costs you nothing in time or effort, makes people safer, and helps reduce the need for other restrictions.
The authors are a Cambridge University Physicist and Biologist, who have been finding the lack of ventilation extremely frustrating, as it is the single most effective thing we could do to reduce risk, without imposing cost, harming the economy, or needing to add even
further social restrictions.
And yet most people don't know, don't understand, and the public health messaging says very little - though this is finally beginning to change.
I have also had extensive discussions with multiple engineers and biologists. I am a scientist and engineer (and so I can visualise fluid dynamics and airflow), but I'm not an epidemiologist.
If there is something here which is factually wrong, please let me know and I'll correct it - outdated messages, or misinformation are harmful. If there's a better resource on this, we'll link to it, or redirect.
Copyright: please feel free to share this, link it, or copy it wholesale. Anything here is placed into the public domain.
Last updated: 30th Dec 2020.
Contact: send email to:
contact AT openyourdamnwindows DOT com.
As of December 2020, the vaccine is coming on-stream, but expected to take many months to reach full coverage. We also have increased transmissibility, and the newer variants have evolved to be more infectious, increasing "R". So, we really have to go all-out.
However, the economic, social, and mental-health costs of indefinite lockdown are mounting; while we must do everything to speed the vaccinations, we still need to find more ways of "living in a world which has the virus prevalent", rather than just "waiting it out".
We have to leverage all our creativity and effort to find options. Doing more of the same is not sufficient. more