A New Study of COVID-19 Transmission Questions the Adequacy of the Six-Foot Rule and the Rationale for Many Occupancy Limits

The researchers highlight the danger posed by tiny, well-circulated respiratory droplets.


A new MIT study of COVID-19 transmission casts doubt on both the adequacy of physical distancing guidelines and the rationale for occupancy limits in large, well-ventilated indoor settings. The study, published this week in Proceedings of the National Academy of Sciences, highlights the danger from tiny respiratory droplets that circulate throughout a room, which cannot be avoided by maintaining a distance of six feet from other people, as long recommended by the Centers for Disease Control and Prevention.

The authors—Martin Bazant, a professor of chemical engineering and mathematics, and John Bush, a professor of applied mathematics who specializes in fluid dynamics—note that the six-foot rule assumes "the primary vector of pathogen transmission is the large drops ejected from the most vigorous exhalation events, coughing and sneezing." The rule makes sense based on that assumption, since "high-speed visualization of such events reveals that [six feet] corresponds roughly to the maximum range of the largest, millimeter-scale drops."

But "there is now overwhelming evidence that indoor airborne transmission associated with relatively small, micron-scale aerosol droplets plays a dominant role in the spread of COVID-19." The six-foot rule does not address that risk. In fact, Bazant and Bush say, "one is no safer from airborne pathogens" at 60 feet than at six feet when the air is well-mixed.

"We argue that, in the context of airborne transmission in a well-mixed space, the benefits of the six-foot rule are limited," Bazant told Fox News. "As everyone in the room is breathing the same air, they share the same risk. Social distancing may thus be giving you a false sense of security. However, we note that the six-foot rule is valuable in limiting transmission by respiratory jets [such as those emitted by coughs and sneezes], which pose a heightened risk when people are not wearing masks."

Using data from earlier research, including studies of COVID-19 superspreading events, Bazant and Bush developed a model that estimates indoor transmission risk based on factors such as ventilation, the size of the space, the number of people present, the level of activity (e.g., singing, shouting, or exercising vs. quiet speech or resting), the use of face masks, and the amount of time spent in the space. They found that some safeguards can have a dramatic impact on the likelihood that a carrier will spread the virus.

In "a typical American classroom, designed for an occupancy of 19 students and their teacher," for instance, "the safe time after an infected individual enters the classroom is 1.2 [hours] for natural ventilation and 7.2 [hours] with mechanical ventilation." That's assuming "a quiet classroom," where "resting respiration is the norm." When masks are added, "these bounds are increased dramatically, to 8 and 80 [hours], respectively." If students spend six hours a day in the classroom, "a school group wearing masks with adequate ventilation would thus be safe for longer than the recovery time for COVID-19," and "school transmissions would be rare," which jibes with what has been observed after schools are reopened.

Bazant and Bush's estimates are much less reassuring for "elderly homes and long-term care facilities, which account for a large fraction of COVID-19 hospitalizations and deaths." Based on New York City's rules for nursing homes, which allow up to three residents per room and require at least 80 square feet each, and assuming natural ventilation, "the Six-Foot Rule fails after only [three minutes] under quasi-steady conditions, or after 17 [minutes] for the transient response to the arrival of an infected person." Even with mechanical ventilation, "three occupants could safely remain in the room for no more than 18 [minutes]" in the steady-state scenario.

"This example provides insight into the devastating toll of the COVID-19 pandemic on the elderly," Bazant and Bush write. "It underscores the need to minimize the sharing of indoor space, maintain adequate, once-through ventilation, and encourage the use of face masks."

Bazant and Bush's calculations also suggest that government-imposed occupancy limits, a common response to the pandemic, make sense only in some indoor settings. "Our analysis shows that many spaces may be safe to reopen at full occupancy, while others carry significant risk," Bazant told Fox News, "depending on the amount of time people spend together, the ventilation rate, whether face masks are worn, and other factors."

Bazant and Bush have created an online app that calculates the maximum recommended cumulative exposure time (CET) in various settings. The parameters include age group, viral strain, "room specifications" (classroom, living room, church, restaurant, etc.), and "human behavior," including mask use and activity level. The "advanced mode" of the app includes additional factors, such as infection prevalence and population immunity.

After a person infected by the Wuhan strain enters a church occupied by 100 people who are wearing masks and speaking but not singing, for instance, the basic app says the CET should be no more than 17 hours. Assuming a one-hour service, the app recommends an occupancy limit of 211 people. For a commercial airliner with the same number of people, the maximum CET is 54 hours. The recommended maximum occupancy for an eight-hour flight is 160 passengers. Those estimates assume that a 10 percent risk of airborne transmission is tolerable.

"Often times the space is large enough, the ventilation is good enough, and the amount of time people spend together is such that those spaces can be safely operated even at full capacity, and the scientific support for reduced capacity in those spaces is really not very good," Bazant told CNBC, mentioning large university classrooms as an example. "I think if you run the numbers, even right now, for many types of spaces, you'd find that there is not a need for occupancy restrictions."

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  1. which jibes with what has been observed after schools are reopened.

    Now explain how/why it doesn’t jibe with schools that never closed?

    (Not so) Interesting that the app seems to take precisely *zero* account for age.

    1. “The parameters include age group,… ”

      It’s literally the first thing listed in the article. Try reading.

      1. You’re right, I was imprecise. It’s an underlying epistmological issue in that it’s not accounting for morbidity/mortality. It gives 64+ yr. olds a ‘relative susceptibilty’ score of 1.0 and assigns <15 yr. olds a relative score of 0.23. But that doesn't, in any way jibe with the the fact that children are orders of magnitude less likely to suffer symptoms and/or be hospitalized. And that doesn't even address the fact that that a classroom of 15 yr. olds gets the same s[r] as a church of 15-yr.-olds as an office of 15-yr.-olds… I don't know that I've ever been in a church/restaurant/airplane/subway car that was strictly 64+.

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        2. “orders of magnitude less likely to suffer symptoms ”
          some advice: don’t exaggerate

  2. So now with this study, mask efficacy studies, and the reality that the death count will be much lower this year since it killed them this year, plus vaccinations…why was Joe Biden wearing a mask on a zoom call, and Harris standing 20 feet away from her interviewer.

    Optics. That is all the left has, all they want, and they have a willing media to go along with it.

    1. To be fair, do you want to see Biden’s face and would you want to stand closer to Harris if the other option was 20 feet away?

  3. In fact, Bazant and Bush say, “one is no safer from airborne pathogens” at 60 feet than at six feet when the air is well-mixed.

    Well then we’ll just have to stand sixty-one feet apart, smart guy.

  4. Great, now I have to DEFEND the CDC and Fauci?

    1. Yes. Fuck yes! Finally, someone says what we’re all thinking!

      Oh, sorry. I thought you said DEFUND them. My mistake.

      1. Reading is fendemental skill.

  5. Do you want freedom, or subservience to an MIT study and CDC bureaucrats? Time to pick a side.

    I just walked into a post office and shipped a package, all without a mask. Nobody said a thing.

    1. Let me guess; ‘shall issue’ state?

      1. Yeah, No. New Jersey.

        1. probly shoulda been masked starting about 1994

        2. Really? Holy shit; it can’t have been North Jersey, COVID Karen’s natural habitat.

          1. I try my best to avoid those Godless northerners. The South (Jersey) shall rise again!!

            1. The problem with this sentiment is that nobody actually knows what South Jersey is, mostly because there is no consensus on the boundaries for Central Jersey.

              The one thing we should all agree on: Bergen County is an awful fucking place.

              1. If you are truly from south Jersey you tell folks you’re from Philly.

            2. LOL…Indeed. They’re Godless heathen up north. 🙂

            3. Mother Leeds didn’t give birth to 13 babies for nothing.

    2. ANd you’re proud of yourself for declaring that you are an asshole

  6. However, we note that the six-foot rule is valuable in limiting transmission by respiratory jets [such as those emitted by coughs and sneezes], which pose a heightened risk when people are not wearing masks.

    Here we are 14 months later. 6 ft is arbitrary. Don’t cough and sneeze on other people. Old people are at risk.

    The ratio of smart people and stupid people does not change as population increases, but the ratio of the impact each group has on the other rises proportionally for the smart while increasing exponentially for the stupid.

    1. Don’t stupid people reproduce more?

      1. Yes. Because they don’t realize where the little guys come from.

    2. I always thought this was weird for a grocery store/box store since really don’t think I’ve ever passed by someone coughing or sneezing. Not that they don’t cough or sneeze in the store it’s just that it doesn’t happen when your rolling a cart by in any substantial numbers so why require them there if we are not in the store long and the chance of being coughed or sneezed on is rare?

  7. Using the app, it’s really astounding what a huge difference masks make. In a church service with 100 people, if everyone is wearing masks the time until transmission is 17 hours, far longer than a normal church service, which usually lasts 60 to 90 minutes. Without them it decreases to 35 minutes!

    This is really frustrating for two reasons. First, it shows that as long as people masked up, all these economy destroying lockdowns probably weren’t needed. We could have just done business as usual, but with strictly enforced mask mandates, and still contained the virus. The second thing is that it makes anti-maskers look like even bigger jerks. If they’d all worn masks this thing could have been contained months ago, without blowing up the economy.

    1. The second thing is that it makes anti-maskers look like even bigger jerks.

      No, it doesn’t. It makes them look like people reacting to the mandates that you have to wear a mask everywhere you go, outside or not, and maintain six feet separation from all other people, outside or not, which “The Science” has never supported.

      Them suddenly saying “oh, gee, I guess it looks like it only makes a difference for prolonged indoor exposure,” which most people knew already, does not make “anti-maskers look like even bigger jerks.”

      1. Anti maskers refuse to wear masks ANYWHERE! That’s the problem. If they just refused to wear them in outdoor spaces or other places where science shows transmission is unlikely, that would be one thing. But they’re so committed to their conspiracy theories they refuse to wear them even where science DOES show them to be effective. Witness the douche above who was proud of entering an indoor space without a mask.

        1. It’s actually to piss off nanny staters who think immortality is a worthy pursuit.

    2. Say I concede the transmission time part to you, your second part of this that this thing would be contained if they’d all worn masks isn’t true. What about all the state mandates why did numbers go up after mask requirements and keep going up? That doesn’t look like containment from an apparatus to me.

      1. Why make such a concession? Its not as if the proposition that the CET app is accurate, much less irrefutable.

        1. Valid point.

        2. Okay Mike.
          We’ll be looking for your journal article

      2. Yeah, digging for how/where they identified ‘superspreader’ events and what parameters they snatched out of the air for those.

        1. SARS-CoV-2 Superspreading Events (Blog and database by Koen Swinkels and collaborators)

          *follows link*

          Note that the database is NOT a representative sample of superspreading events. Please read this article for more information about the limitations of the database

          Clear as mud.

          1. Column: Face Mask
            2046 total rows
            2038 empty rows
            4 “yes”
            3 “no”
            1 “Air purification”

            Interesting that they chose to extrapolate their mask data from such specious and slightly contradictory, uh, evidence.

            1. And at least one of the ‘no’s and two of the ‘yes’s are highlighted as being uncertain.

      3. Mask mandates are only good insofar as they’re followed or enforced. Eg plenty of Californians completely ignore their state mandates, which is probably a big reason cases are so high there.

    3. In a church service with 100 people, if everyone is wearing masks the time until transmission is 17 hours, far longer than a normal church service, which usually lasts 60 to 90 minutes. Without them it decreases to 35 minutes!

      1. What church do you go to where everyone is speaking for 35 min.?

      2. See above, this is strictly transmission and doesn’t appear to take (e.g.) average age into account, how we know transmission occurred, etc.

      1. Mad one,
        Someone does not have to be speaking or singing all the time, just more frequently than the half-life residence time of the aerosols in the air.

  8. Stay home if you are sick.
    Wash your hands.
    Cough or sneeze into your handkerchief.
    Close nothing.
    Limit capacity nowhere.
    Go to work.
    Go to school.

    Just like every other damn virus.

    1. Just like the “health commercials” said in Feb/March of last year.

    2. If we treated it like any other virus – H1N1 for example – we wouldn’t have been spared the mean-tweets of the Bad Orange Man.
      Keep your eyes on the reason for the panᵈᵉᵐic.
      It had nothing to do with public health.

  9. Robot from Lost in Space on line 2.

  10. Sullum seems like a low key panic porn person. he doesn’t really want you to know he’s all in on his fear but it’s there semi hidden in a trying to be hipster style.

  11. This study is obviously bullshit as all the experts in the comments here have repeatedly assured us masks don’t do anything

    1. definition of expert these days is pretty broad so makes sense

      1. MT,
        since your a liberty-loss paranoid with no concept of how research scientists establish the credibility of their work, your opinion about expertise is worthless.

        1. If you’re not paranoid about losing your liberty, you really haven’t been paying attention.
          Or, you’re only paying attention to those who want to take it.

    2. Now do the 6-foot-rule.

      1. The six foot rule makes a lots of sense with respect to droplet transmission. If you are hit by a droplet you absorbs many times the number of virions, thus increasing your chance of infection.
        Notice that the study did not claim that aerosol transmission is the only means of transmission.
        And even for droplets 6 ft is not quite far enough.

    3. No, the actual data in the actual real world have convinced us that masks do nothing.

    4. When there’s no study that can find a significant effect on transmission of a respiratory disease from mask wearing, a model using a factor 10 difference between masks and no masks seems pretty suspect. A factor of 10x should literally be unmissable in any real world data.

      1. If anyone were actually stupid enough to do that experiment. Perhaps you might.

  12. I knew it! We need to dump our masks and seal ourselves into large garbage bags. No germs can get me in here!

    1. We are just one authority figure away from a Jonestown mass suicide once they announce the best way to prevent the spread is to tie a plastic bag around your head.

      If it weren’t so unethical, I’d really like to see an experiment.

  13. Heh:

    To limit COVID-19 transmission* in a population with an infection prevalence1 of 99,999 per 100,000, this space should have no more than:
    2 people for >14 days
    5 people for >14 days
    10 people for 240 hours (10 days)
    25 people for 39 hours
    100 people for 3 hours

  14. Hey Sullum,
    Are you going to wear your face mask for the rest of your life?

  15. What utter hooey. That completely misunderstands the Wells Curve.

    Yes, the larger droplets fall to the ground within six feet. And the smaller droplets evaporate within six feet. Yes, the Wells Curve makes a lot of assumptions about relative humidity, etc. It’s at best a rule of thumb. But these clowns seem to have ignored that entirely.

    More to the point, most everyone else in the world including the WHO say that 1 meter (3 feet) is adequate and they have no higher incidence of infection because of that.

    As near as I can tell, this “study” was based entirely on computer models with no validation against empirical observations. That’s not Science – that’s hypothesis masturbation.

    1. This was exactly my thought.

    2. …and asymptomatic spread is a lie (0.7%). So the entire premise that everybody has to mask up cause you don’t know who might spread it is garbage. If you don’t have symptoms you aren’t spreading it anyway.

    3. “was based entirely on computer models with no validation”
      Actually the model is completely consistent with many aerodynamics experiments done at MIT.
      ” – that’s hypothesis masturbation.”
      That comment is arrogant mental masturbation

  16. “…maintaining a distance of six feet from other people, as long recommended by the Centers for Disease Control and Prevention.”

    Where “long” in this case means since March of last year.

    And of course course neither the study nor the article about it points out that healthy people don’t spread respiratory diseases.

  17. Fuck it, let’s just make vocalization illegal. We’ll all learn sign language. And everyone will need binoculars to see what the person 61 feet away is trying to say. Full gas masks for all. You can go to the mall but only if you’re wearing a full hazmat suit. If it saves just one life, amiright?

    Or we could finally accept our mortality, recognize that being alive is risky, and that much communication is non-verbal, which is why masks are more than a minor inconvenience.

    I don’t have pandemic fatigue so much as I have “New Study Shows We Were Right the 8th Time” fatigue.

    1. Easy to do in the People’s Republic of NJ = sign language.

      All sign language here begins with a raised middle finger.

  18. If I die of COVID at least I will still be able to vote and cash stimulus checks.


    1/ I’m watching baseball tonight and out of nowhere the announcers start talking about the vaccine, how easy it getting it was, how great it is… and the stadium signage says “Take one for the team. Get vaccinated.” (Not exactly the message I’d send, but I digress.)…

    2/ Two tiny tendrils of this overwhelming campaign, not just nationally but internationally coordinated on so many fronts – get vaccinated and fly to Europe or go to college or get free donuts –

    And help me out here. I cannot think of another example remotely like this…

    3/ Where democratic governments, NGOs, private companies, academia, and the media have massed to dictate an outcome to an obviously reluctant citizenry – but without quite compelling them. I mean, democracies used to draft soldiers, but that basically ended with Vietnam…

    4/ Because that war was so unpopular. But this feels more like trying to recruit a VOLUNTEER army for Vietnam – Save Granny, kill Commies! Enlist, get free donuts for a year –

    And the harder they push, the more anyone on the fence will wonder just WHY they’re pushing so hard –

    5/ But to go back to the original question – can anyone think of any campaign like this? – not just in the democratic era, but before? It feels vaguely Soviet, sure, but the Soviets didn’t have a real private sector or NGOs to play along.

    Honest question. Interested in answers.

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  21. The confirmation that it probably spreads by aerosols is nice. But why do they think that masks make a *factor or 10* difference in transmission rates? Surely we’d have good evidence of mask efficacy if they were that effective. When the literature can’t find an effect of masks on transmission rates, that’s a problem for a model with a factor 10 effect – that should be unmissable.

    1. ” But why do they think that masks make a *factor or 10* difference in transmission rates?”
      Because masks with a smaller than 1 µm filter remove most of the virions

      1. Where’s the data supporting a factor of 10, specifically?

        And why is there no literature documenting such a huge effect size? Even attempts to documement n95 efficiency against transmission of respiratory viruses doesn’t show much in the way of an effect. The literature is painfully against such a huge degree of effectiveness.

        A factor 10 effect is gigantic. You’d see massive significance in the data if it was real. You don’t.

        1. The documenting literature is all smeared from being pulled out of the guy’s ass.

  22. A New Study of COVID-19 Transmission Questions the Adequacy of the Six-Foot Rule and the Rationale for Many Occupancy Limits

    Long before COVID-19, and not for medical reasons, but for general purposes, I have wanted to tell a whole Hell of a lot of people:

    “Don’t limit yourself to 6 feet! There are 2 Continents to the South and 4 Continents to the East! GO!!!”

  23. When masks are added, “these bounds are increased dramatically, to 8 and 80 [hours], respectively.”

    If you added enough cloth masks to overcome the fact they don’t filter “micron-scale aerosol droplets” then you’d asphyxiate the wearer.

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