Sneezes and coughs are so routine that no one really thinks of them as serious health hazards. And health hazards they might not be, but these “violent expiratory events” do aid the spreading of diseases.
At the Massachusetts Institute of Technology in Cambridge, a project lead by Lydia Bourouiba, is studying the fluid dynamics of a sneeze. To record sneezes the team uses high speed cameras that can capture thousands of frames per second.
Played back in slow motion the footage shows mucous and saliva being expelled in a turbulent cloud made up of droplets. It's not a pretty sight. The smaller droplets are carried a long way because of this cloud dynamic, but even the bigger ones can travel farther than previously believed, depending on the environmental conditions.
Footage of mucous and saliva being expelled by people is about as gross as it sounds, but it's really helpful in the interest of science, especially in understanding how infections can spread.
The video above by science journal Nature takes us inside the lab and explains very broadly the research and its implications.
Bourouiba says, “Sneezes are actually really interesting. They are multi-phased, turbulent clouds so there’s all sorts of scales also involved, but at the same time it is a complex flow because you have a gaseous phase, that is coupled with droplets and eventually the final residue of these drops which could be solid residues containing the pathogens and so there’s a lot of very interesting open problems of physics and free dynamics embedded in it”.
The recorded videos help her in measuring everything from the diameter of the droplets to their speed. While previously it was believed that larger droplets didn’t travel than further than 1-2 metres, video evidence coupled with cloud dynamics shows that even the larger ones can. “Up to 8 metres for a sneeze and 6 metres for a cough depending on the environmental conditions, and stay suspended for up to 10 minutes – far enough and long enough to reach someone at the other end of a large room, not to mention the ceiling ventilation system” a report in Nature says.
Another previously held belief was that the droplets from sneezing exited fully formed, but these videos reveal that the fluid breaks up in steps. It emerges from the mouth in sheets, which then stretched by the airflow, puncture and form rings. The rings get fractured into filaments, from which the droplets are finally produced. You can read more about the project here and here.
Oh and how is the sneezing induced? By tickling the subject’s nose. The researchers tried other methods as well, but to induce a natural sneeze, it’s now scientifically proven that nose tickling is the most reliable method.
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