Free Republic
Browse · Search
General/Chat
Topics · Post Article

Skip to comments.

In the cloud: How coughs and sneezes float farther than you think
MIT News Office ^ | April 8, 2014 | Peter Dizikes

Posted on 04/08/2014 1:33:52 PM PDT by glorgau

The next time you feel a sneeze coming on, raise your elbow to cover up that multiphase turbulent buoyant cloud you’re about to expel.

That’s right: A novel study by MIT researchers shows that coughs and sneezes have associated gas clouds that keep their potentially infectious droplets aloft over much greater distances than previously realized.

“When you cough or sneeze, you see the droplets, or feel them if someone sneezes on you,” says John Bush, a professor of applied mathematics at MIT, and co-author of a new paper on the subject. “But you don’t see the cloud, the invisible gas phase. The influence of this gas cloud is to extend the range of the individual droplets, particularly the small ones.”

Indeed, the study finds, the smaller droplets that emerge in a cough or sneeze may travel five to 200 times further than they would if those droplets simply moved as groups of unconnected particles — which is what previous estimates had assumed. The tendency of these droplets to stay airborne, resuspended by gas clouds, means that ventilation systems may be more prone to transmitting potentially infectious particles than had been suspected.

With this in mind, architects and engineers may want to re-examine the design of workplaces and hospitals, or air circulation on airplanes, to reduce the chances of airborne pathogens being transmitted among people.

“You can have ventilation contamination in a much more direct way than we would have expected originally,” says Lydia Bourouiba, an assistant professor in MIT’s Department of Civil and Environmental Engineering, and another co-author of the study.

The paper, “Violent expiratory events: on coughing and sneezing,” was published in the Journal of Fluid Mechanics. It is co-written by Bourouiba, Bush, and Eline Dehandschoewercker, a graduate student at ESPCI ParisTech, a French technical university, who previously was a visiting summer student at MIT, supported by the MIT-France program.

Smaller drops, longer distances

The researchers used high-speed imaging of coughs and sneezes, as well as laboratory simulations and mathematical modeling, to produce a new analysis of coughs and sneezes from a fluid-mechanics perspective. Their conclusions upend some prior thinking on the subject. For instance: Researchers had previously assumed that larger mucus droplets fly farther than smaller ones, because they have more momentum, classically defined as mass times velocity.

That would be true if the trajectory of each droplet were unconnected to those around it. But close observations show this is not the case; the interactions of the droplets with the gas cloud make all the difference in their trajectories. Indeed, the cough or sneeze resembles, say, a puff emerging from a smokestack.

“If you ignored the presence of the gas cloud, your first guess would be that larger drops go farther than the smaller ones, and travel at most a couple of meters,” Bush says. “But by elucidating the dynamics of the gas cloud, we have shown that there’s a circulation within the cloud — the smaller drops can be swept around and resuspended by the eddies within a cloud, and so settle more slowly. Basically, small drops can be carried a great distance by this gas cloud while the larger drops fall out. So you have a reversal in the dependence of range on size.”

High-speed imaging has helped MIT researchers determine that some droplets from coughs and sneezes may carry much farther than previous studies had estimated.

Video courtesy of the researchers

Specifically, the study finds that droplets 100 micrometers — or millionths of a meter — in diameter travel five times farther than previously estimated, while droplets 10 micrometers in diameter travel 200 times farther. Droplets less than 50 micrometers in size can frequently remain airborne long enough to reach ceiling ventilation units.

A cough or sneeze is a “multiphase turbulent buoyant cloud,” as the researchers term it in the paper, because the cloud mixes with surrounding air before its payload of liquid droplets falls out, evaporates into solid residues, or both.

“The cloud entrains ambient air into it and continues to grow and mix,” Bourouiba says. “But as the cloud grows, it slows down, and so is less able to suspend the droplets within it. You thus cannot model this as isolated droplets moving ballistically.”

Ready for a close-up

Other scholars say the findings are promising. Lidia Morawska, a professor at Queensland University of Technology in Brisbane, Australia, who has read the study, calls it “potentially a very important paper” that suggests people “might have to rethink how we define the airborne respiratory aerosol size range.” However, Morawska also notes that she would still like to see follow-up studies on the topic.

The MIT researchers are now developing additional tools and studies to extend our knowledge of the subject. For instance, given air conditions in any setting, researchers can better estimate the reach of a given expelled pathogen.

“An important feature to characterize is the pathogen footprint,” Bush says. “Where does the pathogen actually go? The answer has changed dramatically as a result of our revised physical picture.”

Bourouiba’s continuing research focuses on the fluid dynamics of fragmentation, or fluid breakup, which governs the formation of the pathogen-bearing droplets responsible for indoor transmission of respiratory and other infectious diseases. Her aim is to better understand the mechanisms underlying the epidemic patterns that occur in populations.

“We’re trying to rationalize the droplet size distribution resulting from the fluid breakup in the respiratory tract and exit of the mouth,” she says. “That requires zooming in close to see precisely how these droplets are formed and ejected.”

Funding for the study was provided by the National Science Foundation.


TOPICS: Health/Medicine
KEYWORDS: cold; cough; flu
Money line is that stuff goes 200 times further than previously thought.
1 posted on 04/08/2014 1:33:52 PM PDT by glorgau
[ Post Reply | Private Reply | View Replies]

To: glorgau

We hide from this stuff we’re never gonna build up resistance.


2 posted on 04/08/2014 1:37:17 PM PDT by Vaquero (Don't pick a fight with an old guy. If he is too old to fight, he'll just kill you.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: glorgau
I will never laugh at these people again...


3 posted on 04/08/2014 1:38:03 PM PDT by cuban leaf
[ Post Reply | Private Reply | To 1 | View Replies]

To: Vaquero

Antibodies - Use them or lose them.


4 posted on 04/08/2014 1:38:41 PM PDT by dfwgator
[ Post Reply | Private Reply | To 2 | View Replies]

To: glorgau

Gesundheit.


5 posted on 04/08/2014 1:39:05 PM PDT by Constitution Day
[ Post Reply | Private Reply | To 1 | View Replies]

To: glorgau

The way I read it was five to 200 times farther.


6 posted on 04/08/2014 1:39:50 PM PDT by loungitude (The truth hurts.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: glorgau

So the stupid custom of coughing or sneezing into one’s hand is really a dumb idea because the hand then touches doorknobs, surfaces, papers, books, hands, etc?


7 posted on 04/08/2014 1:42:54 PM PDT by I want the USA back (Media: completely irresponsible traitors. Complicit in the destruction of our country.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: cuban leaf

I never did


8 posted on 04/08/2014 1:44:32 PM PDT by knarf (I say things that are true .. I have no proof .. but they're true.)
[ Post Reply | Private Reply | To 3 | View Replies]

To: glorgau

I sneezed once into my elbow joint and got a torn rotator cuff. I can’t ever win.


9 posted on 04/08/2014 1:46:08 PM PDT by Safetgiver ( Islam makes barbarism look genteel.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: glorgau

bookmark


10 posted on 04/08/2014 1:47:31 PM PDT by GOP Poet
[ Post Reply | Private Reply | To 1 | View Replies]

To: glorgau

11 posted on 04/08/2014 1:48:27 PM PDT by DannyTN
[ Post Reply | Private Reply | To 1 | View Replies]

To: glorgau
I sneezed a sneeze into the air
It fell to the earth I know not where
But hard and froze were the looks of those
In whose vicinity I snoze.
12 posted on 04/08/2014 1:49:02 PM PDT by Sgt_Schultze (A half-truth is a complete lie)
[ Post Reply | Private Reply | To 1 | View Replies]

To: Safetgiver

Chuck Norris sneezed twice. He has never again given permission after what happened to Nagasaki.


13 posted on 04/08/2014 1:51:43 PM PDT by DariusBane (Liberty and Risk. Flip sides of the same coin. So how much risk will YOU accept? Vive Deco et Vives)
[ Post Reply | Private Reply | To 9 | View Replies]

To: glorgau

Don’t tell me...another cause of “global warming?”


14 posted on 04/08/2014 2:10:17 PM PDT by goodnesswins (R.I.P. Doherty, Smith, Stevens, Woods.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: dfwgator
Bubble boy: the Moors

George: you're wrong. The answer is The Moops.


15 posted on 04/08/2014 2:11:02 PM PDT by Vaquero (Don't pick a fight with an old guy. If he is too old to fight, he'll just kill you.)
[ Post Reply | Private Reply | To 4 | View Replies]

To: glorgau
This is one of the reasons to install UV Duct Lights as part of your furnace air circulation system.
16 posted on 04/08/2014 2:13:40 PM PDT by PA Engineer (Liberate America from the Occupation Media.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: Safetgiver
"I sneezed once into my elbow joint and got a torn rotator cuff."

That was one heck of a sneeze.

17 posted on 04/08/2014 2:31:45 PM PDT by Flag_This (Liberalism: Kills countries dead.)
[ Post Reply | Private Reply | To 9 | View Replies]

To: Vaquero

That’s what I say.


18 posted on 04/08/2014 2:42:59 PM PDT by FrdmLvr ("WE ARE ALL OSAMA, 0BAMA!" al-Qaeda terrorists who breached the American compound in Benghazi)
[ Post Reply | Private Reply | To 2 | View Replies]

To: Sgt_Schultze

Haha! Pretty good!


19 posted on 04/08/2014 2:44:22 PM PDT by FrdmLvr ("WE ARE ALL OSAMA, 0BAMA!" al-Qaeda terrorists who breached the American compound in Benghazi)
[ Post Reply | Private Reply | To 12 | View Replies]

To: PA Engineer

Thanks for the info!


20 posted on 04/08/2014 2:47:11 PM PDT by FrdmLvr ("WE ARE ALL OSAMA, 0BAMA!" al-Qaeda terrorists who breached the American compound in Benghazi)
[ Post Reply | Private Reply | To 16 | View Replies]

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.

Free Republic
Browse · Search
General/Chat
Topics · Post Article

FreeRepublic, LLC, PO BOX 9771, FRESNO, CA 93794
FreeRepublic.com is powered by software copyright 2000-2008 John Robinson