Study shows how long the breath of a sick person stays in the air

Study shows how long the breath of a sick person can affect healthy people.

older woman wearing a covid mask

Respiratory droplets from a cough or sneeze travel farther and last longer in humid, cool climates than in hot, dry ones, according to a new study on droplet physics.

Scientists from the University of California San Diego have created a model that that can predict the early spread of respiratory viruses including COVID-19, and the role of respiratory droplets in that spread.

They now better understand the role that droplet clouds play in the spread of respiratory viruses, including how long the breath of a sick person can affect healthy people and how far the infected droplets can travel.

“The basic fundamental form of a chemical reaction is two molecules are colliding. How frequently they’re colliding will give you how fast the reaction progresses,” said Professor Abhishek Saha, one of the paper’s authors.

“It’s exactly the same here; how frequently healthy people are coming in contact with an infected droplet cloud can be a measure of how fast the disease can spread.”

Depending on weather conditions, some respiratory droplets travel between 2.4m–4m away from their source before evaporating, without accounting for wind.

This means that without masks, the currently mandated 1.5m of social distance may not be enough to keep exhalated particles from reaching someone else.

“Droplet physics are significantly dependent on weather,” said Prof. Saha.

“If you’re in a colder, humid climate, droplets from a sneeze or cough are going to last longer and spread farther than if you’re in a hot, dry climate, where they’ll get evaporated faster. We incorporated these parameters into our model of infection spread; they aren’t included in existing models as far as we can tell.”

The researchers hope their work will help inform public health policies and be used in the future to better understand the role of environmental factors in virus spread.

They also found that at 35°C and 40 per cent relative humidity, a droplet can travel about 2.4m. However, at 5°C and 80 per cent humidity, a droplet can travel up to 3.6m.

The team also found that medium-sized droplets possess higher risk as they take longer to evaporate and travel greater distances. Whereas smaller droplets evaporate within a fraction of a second, while larger droplets quickly settle to the ground due to weight.

The research provides further evidence of the importance of wearing masks in public.

The team is now working to learn more about how COVID-19 droplets spread and how long they live on surfaces.

“Our next step is to relax a few simplifications and to generalise the model by including different modes of transmission,” said co-author Professor Saptarshi Basu.

“A set of experiments are also underway to investigate the respiratory droplets that settle on commonly touched surfaces.”

Do you think this research provides further evidence backing the need to wear masks in public?

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    24th Jul 2020
    All of this contradictory research proves that no one really knows what’s happening, there was a report yesterday that said that the scientists have been modelling their research on how the flu spreads, they now realise that the two infections are completely different, maybe the best idea might be to stop publishing their findings until they can get some agreement amongst themselves that they are on the right track, or is it more important for them to be able to say we got it right first?
    24th Jul 2020
    Jim, there is no logical connection from their being lots of research, lots of new facts being discovered, lots of debate and sharing and severe problems propelling it all, to your silly sequitor that nobody knows anything.

    One could possibly argue that nobody knows everything, but there is lots of evidence that many know much, - about covid and about almost everything else, so your conclusion is null and void and without merit and could cause immense damage if any one else accepts such foolishness.

    We are all in this together Jim, we have to solve it together, your comment is best descibed as ignorant despair, so not any help at all, - hopefully you will start thinking and find a more helpful mindspace.

    One suggestion, "Cherry Picking" is not a logical nor sensible process.

    What your 'process' evades, is that the covid 19 Virus is both smarter and more adaptive, therefore more able to breed, to spread faster and do more damage than initially known, - we hide from these important Facts at our extreme peril.

    Apologies for being blunt Jim, but remembering the old adage, " if you are not part of the solution you are part of the problem", your current thought forms are part of the problem. - let them go, please.
    24th Jul 2020
    Jim's entitled to his opinion. I was interested to read it. Your comment is in no way ignorant. You don't have to "let anything go" on the basis that your view doesn't suit someone else. You have a right to express it. Don't stop saying your opinion, Jim.
    24th Jul 2020

    Why is Jim not allowed to express an opinion which differs from yours but is in line with a lot of other commentators.

    You are not being blunt but arrogant and insulting. 100 people would have 100 different opinions on the subject and yours is just another without any scientific backing. It is just your opinion and nothing more.
    24th Jul 2020
    Lookfar, on further thought regarding your directives to Jim: Attempts to cancel honest viewpoints drives thoughtful people away. Is that what we really want in Australia? Shut people up so that only the few self-entitled so-called "intellectuals", nutty university academics and nutty minority groups can get control over the majority? Have your say no matter what, Jim.
    24th Jul 2020
    Hey Jim, it's just normal research you get on many health issues - one day too many eggs are bad for you, the next day they are good for you same with chocolate, coffee, salt, etc, etc.

    They are learning along the way and yes I think sometimes the "I got it right first" attitude is there.

    Like I said elsewhere it's all about compromise, there is no hard and fast way to combat this, we can only follow what's recommended (or mandated) by the health departments and we'll get through long as most people take it seriously, that's where we fall down unfortunately.
    24th Jul 2020
    Lookfar are you sure you actually read my comment, from your response it’s seems to me you need to take a chill pill and read it again, there is nothing in my comment that should cause anyone despair, I worked in research for many years, I am fully aware of the vagaries of research, the very nature of research suggests a lack of knowledge, and a desire to attain some understanding, as more information becomes available opinions and direction changes, what you don’t do is continually publish results before they can be proven, unless of course you are going for misdirection. I don’t mind you being blunt, but I do take offence at your baseless insults, you are entitled to your opinion, you are not entitled to denigrate some one else’s just because you don’t agree with them, you have a good night anyway.
    24th Jul 2020
    what was contradictory about this research?
    25th Jul 2020
    Farside, I am not sure if that’s a fair dinkum question, but if it is, then there are lots of contradictions, but the one I eluded to was that the scientist who was on tv stated that most scientists were working on the assumption that the Covid 19 acted in the same way as the flu and they now realise this was incorrect, in research this often happens, my issue isn’t that things change, it’s related to releasing information before having conclusive evidence that the information is correct, which they clearly didn’t have, misinformation is worse then no information. To be clear I didn’t say nobody knows anything, I said know one really knows what’s going on, that’s why it’s called research to try and determine what’s actually happening and to devise a strategy to combat it.
    25th Jul 2020
    Jim, to quote you, " All of this contradictory research proves that no one really knows what’s happening,"

    Is this really the situtation? you appear to assert that it is.
    I have I believe advanced an argument that you were incorrect, you can answer that as you wish, but
    Brissiegirl does the politician thing that I am stopping you from having your say.

    Have I stopped you from having your say?


    The most important thing confronting this our possibly most serious pandemic virus, is that we all need to share and help each other to survive.

    Can you agree to that?

    28th Jul 2020
    my question was fair dinkum Jim, the nature of research when dealing with something novel is to hypothesize from the existing body of knowledge, experiment, make observations, share findings, challenge conclusions and either add to body of knowledge or modify hypothesis, rinse and repeat. They have known it was a coronavirus and not an influenza virus for more than six months but some of the early models for things like transmissibility were based upon those used for influenza and modified, other models were based upon SARS and MERS.
    24th Jul 2020
    I often face people running and/or jogging coming toward me, and pass in close proximity, when undertaking my morning walks in my local park. They are panting and huffing and puffing as they pass and I often wonder how dangerous that could be should one of them prove positive to the corona-19 virus. Living in Sydney, I think it may be time I commenced wearing a mask when doing my walks. Either that, or taking a very wide birth when I see such people coming
    24th Jul 2020
    I wonder though that if you have a mask on and droplets from those huffing and puffing joggers land on it, are you breathing in those, maybe infected, droplets for as long as that mask is on your face?
    24th Jul 2020
    probably Both, CoogeeGuy, - as they have found, it is a question of how many particles of the virus you ingest, - the more the worser, all else being equal.
    24th Jul 2020
    Joggers, runners & serious bike riders on shared bike/walking paths scare me. Even if they might not breath directly on you, the droplets could hang in the air behind them waiting to land on someone. My husband & I stopped walking on the paths near our home because in parts they are so narrow it’s impossible to social distance or avoid runners. I’m pleased that masks are now mandatory in Melbourne but not happy that runners are still allowed to run amongst the rest of us. They should only be able to run far away from other people or in designated areas, or not at all...they could walk instead. Somewhere (Spain I think...not sure) had staggered hours for different groups of people to exercise, e.g. older people only at a certain hour, etc. By the way, for people who think they can’t exercise with a mask, I found it hard when walking on inclines or hills at first but it’s a lot easier now. I think it must be the training effect. The type of mask probably makes a difference too. Mine has a seam down the middle so it has more room inside to breath than some of the flat across the face masks,
    Horace Cope
    24th Jul 2020
    My reading of the efficiency of face masks, CoogeeGuy, tells me that they will stop other people's droplets from entering the mouth and nose as well as stopping droplets being exhaled. They won't stop droplets from landing on other unprotected parts and touching these droplets may cause ingestion if the hand is near the mouth or nose. Droplets can penetrate the eye membranes. Wearing a mask seems to be a good start and it's what we do when we venture out into the public sphere.
    24th Jul 2020
    We had to change our walking routes due to inconsiderate droplet-spraying joggers. They are indeed a worrisome health hazard. I think masks are an additional armour along with regular hand washing, physical distancing and avoiding crowded places. When professionals tell us not to touch the outside of a mask when removing it, isn't that confirmation that a mask can definitely collect external contaminated droplets?
    Just my opinion, but I think a mask in such circumstances when walking close to joggers can't do any harm. It may even be the difference between staying safe and copping someone else's infectious spray.
    Horace Cope
    24th Jul 2020
    "Do you think this research provides further evidence backing the need to wear masks in public?"

    It matters little what I think, I am relying on the medical advice that drives the government's rules about how we should try and combat this pandemic.
    24th Jul 2020
    Hi Horace, - sometimes good to strike out on your own and not just follow the party line,- politicians are no smarter than the rest of us and sillier than many, and more corrupt than almost everyone.

    Look at the research all over the world, look at how the govt info changes from week to week, - you obviously have access to the Internet, I truly believe you are capable of thinking for your self, - might you not be happier so to do?

    Then you would be a much more self realised person, and probably much more comfortable about your own destiny.
    24th Jul 2020
    Lookfar - You say to "think for yourself" but also say you have access to the internet, no doubt to read up and follow someone else's thoughts?

    No politicians aren't smarter than us BUT as the politicians keep saying repeatedly they are following the advice of health professionals. Apart from Trump I have never heard any politician pretend to know much about this issue, they always say "on best medical advice"
    24th Jul 2020
    Here's a poem I wrote last month:


    People walk by
    Keeping their distance
    2 metres
    3 metres
    4 metres
    And I can still smell
    Their perfume

    Science is crucial, it takes time but without it we're stuffed!
    24th Jul 2020
    Triss and all, various new research is finding that the droplets last longer and go further, - undeestandably it is hard to measure in a cubic metre of air, just how many droplets are both there and alive, particularly as your measurement apparatus may kill the droplets by so measuring.

    Well, new technologies are evolving, new information is being gathered, - currently several respected scientisits are criticising the world health organisation for not passing on the info that droplets can last 3 hours and travel 4 metres.

    In regard to you personal mask, I have suggested to several major authorities that if one's mask is soaked in Borax solution, (as I have shared several times on this site) then allowed to dry so the borax is in the fibres, - dry, - when the globules land on your mask they dissolve the borax, killing it because that dries it but much more because the borax is then in solution, and as it is highly alkaline, kills the virus quickly and absolutely.

    Seems no debate, well science is science, alkaline kills virus, soap solution is alkaline, Borax is much more alkaline and becomes integrated in the mask fibres, whereas soap tends to block the mask airways.

    The borax will protect you longer, because the mask will get damp, so the borax will dissolve more and spread through the mask, killing virus as it goes, so when the mask becomes choked with water, you must change the mask as nothing is getting through.
    To make a borax solution to soak your mask in, buy the cheap cleaning Borax, IGA sells it, and others, app. $5, half a kilogram, - dissolve in Luke warm water until only a small amount of the powder is sitting on the bottom, not dissolving, meaning the solution is 100%, dip in your masks, till soaked, and peg out to dry.

    If you fear you have put in too little borax, try to burn your mask with a cigarette lighter or match, the borax will suppress the flame and the mask will not burn, - borax is ued in natural house insulation for exactly that reason.

    The Borax solution will also do a much quicker and better hand wash than soap as it is more virus deadly and penetrates into the folds of your fingers, etc more quickly, whilst not passing through your skin, but putting a much sounder and longer lasting shield over your skin.

    Finally you can include the borax, as per instructions on washing, in the last rinse of your washing machine cycle of your outer clothing, dry as normal, so the borax will be sitting there invisibly in your outer clothing to destroy the virus as it lands on your clothing, - all adding to less virus on you and in your environment and less spreading to others.

    Hope that helps.
    24th Jul 2020
    Wonder why these "major authorities" didn't follow your advice. LOL
    24th Jul 2020
    What a load of crapp.
    24th Jul 2020
    Diamond, they didn't dare step out of a tiny spot they were chained to, - they could have said no, but they were lost souls, - like Mick, although he seems chained to crap, - glad I don't live in his dysfunctional universe.

    Point is, no one said no. - so let's do it this better way, - Borax, Borax, Borax. Yeh! yeh, Yeh!
    25th Jul 2020
    You are a complete nutter looky far I definitely think you have caught Corona and it has gone to your brain.
    24th Jul 2020
    Just now whilst walking my 2 laps around Centennial Park I conducted experiment. Everyone a runner or jogger approached me I took an obvious wide birth well ahead of their approach. Not one of them made any attempt to deviate from their path and place any distance between us. Plus I noticed large groups of mothers and their children in pram’s congregating in close proximity together having a good old chin wag. From my observations, I do not think we can point any fingers at Victoria, as we NSW people are not behaving any better. I think we have become very complacent, from which this particular virus thrives
    24th Jul 2020
    it seems true, CoogeeGuy, and we in far north queensland are much threatened by such complacency, having virtually eliminated Covid19.
    One possibility is strong Govt penalties, probably would work, - esp if they farmed it out to private companies who gave their staff a commission for every breach, but what a paranoid society that would achieve..

    Perhaps we can start to think of positive re-inforcement possibilities?

    Just wondering..
    24th Jul 2020
    GoogeeGuy and Lookafar, down here in chilly Melbourne it is not much different. My wife and I discontinued our daily walk weeks ago because of the seemingly indifference of some people to observe any semblance of social distancing, it got to be scary. The last straw was crossing a short bridge, about 1.2m wide, over a creek when a lady walking her dog came from the other direction and did/would not wait for us to complete the crossing. When the dog attempted a friendly sniff at us, which we did not mind, she started to yell at it. She apologised for her dog which we told her we were not worried about the dog but we thought we were in more danger from her yelling. After that, and other experiences, we decided it was too hazardous to walk on the bike path. Now our exercise is doing some old fashioned rock 'n roll in our family room, safer and warmer and 'back to the future'.
    24th Jul 2020
    No doubt they COULD travel further but it's all about compromise. Ideally we would all stay home for 2-3 weeks and the virus would be gone, burnout as it had no one to pass it on to but that's not practical. The governments don't want to try to restrict us that much and allow some movement, when we are moving around we try to not be near others for long periods, try not to follow others closely and, now in Melbourne, wear a mask to REDUCE the chances of transmission. Again, a compromise, the best thing would be a divers helmet and oxygen but that's impractical so a mask is just a way to REDUCE the spread.
    24th Jul 2020
    Passing a jogger is dangerous enough but what about a smoker? I hate walking past one and getting a face full of smoke, and still being able to smell it when walking down the path they have just been on. I’d like to know how long droplets last in smoke, and how far they travel when being blown out with force.
    25th Jul 2020
    The research is Gradually becoming available, 4 metres, 3 hours, .. we all should search beyond the local news tp find out what is happenig
    25th Jul 2020
    Just check out a vape smoker to see how far breath can travel 5-10 metres,so wear a mask .
    26th Jul 2020
    Seems like the best solution is to stop breathing. Problem solved!
    28th Jul 2020
    650,000 have tried that around he world, it worked.
    27th Jul 2020
    There is NOTHING contradictory about this research. It is ongoing research based on physics. Since physics is an exact science the research is valuable in determining how far droplets travel and where they fall.
    Yes, this research and similar studies provide more evidence that wearing a face mask makes total sense.

    If it is difficult to get your head around the science of it all. Think of it this way - if you wear a mask, if I wear a mask, if we all wear masks, then we all have a chance of surviving Covid-19.
    28th Jul 2020

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