If you cough or sneeze and you aren’t doing it into the inside of your elbow, you are doing it wrong. (Don’t even think about covering it with your hands. Gross.) A recent study from researchers at MIT have discovered gas cloud properties that allow water droplets and germs to get carried up to 200 times farther than they could travel on their own. The paper was published in the Journal of Fluid Mechanics.
In order to study what the team refers to as “violent expiratory events,” high speed cameras were used. The film was slowed down so they could analyze the size, velocity, and distance traveled by the water droplets.
Ultimately, the team found that water droplets 100 micrometers long are capable of going five times faster than previously predicted. Droplets that are 10 micrometers long can remain airborne up to 200 times farther than previous estimates. This greatly extends the range at which someone with a respiratory illness can infect others.
Extending the range at which these droplets travel are gas clouds that surround the particles. The cloud is comprised of air from the environment as well as water droplets from the sneezer. Co-author John Bush had this to say in a press release:
“When you cough or sneeze, you see the droplets, or feel them if someone sneezes on you, 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.
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, 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.”
By better understanding the means that pathogens have to travel, design of hospitals, airplanes, and other public spaces could be redesigned to minimize the spread of disease. Future studies will continue studying the fluid dynamics of sneezes and coughs in order to get a better handle on epidemics of airborne infectious pathogens.