Six feet might not be enough distance if you are around someone who is coughing, a new simulation suggests, and if you are shorter than the person coughing you are at an even greater risk.
“Although the exact transmission mechanism of SARS-CoV-2 remains unclear, it is generally agreed that the airborne transmission route cannot be dismissed,” the researchers wrote in their study, published this week in the journal Physics of Fluids.
For its study, scientists at Singapore’s Agency of Science, Technology and Research used numerical models to simulate what the trajectory of droplets would be if a person suddenly coughs when outside.
The researchers varied the size of the droplets, the heights of the two people in the simulation, wind speeds, air temperature and humidity.
Not only did the team find that some droplets can travel farther than 6 feet, but also that their trajectory can deposit droplets on anyone shorter than the cougher.
“Young children may be at greater risk compared to adults based on the typical downward cough trajectory,” they wrote. “Teenagers and short adults are advised to maintain a social distance greater than 2 m (6 feet) from taller persons. Surgical masks are known to be effective at trapping large droplets and therefore recommended for use as necessary.”
Highlights and recommendations from the study include:
1. Droplets less than 50 micrometers in diameter can remain airborne over long distances. At wind speeds of 2 meters per second, travel distances for droplet sizes 100 micrometers and 1000 micrometers are 21 feet and 4.25 feet, respectively.
2. Large droplets may travel more than 3.28 feet under windless conditions. The travel distance correlates well with the wind speed. For a 100 micrometer droplet, the travel distance increases from 2.62 feet without wind to 19.7 feet at a wind speed of 10 feet per second.
4. Social distancing is generally effective at reducing the droplet volume as well as the viral load deposited on a person nearby.
5. Droplet deposition on skin and clothes may not directly lead to infection. However, secondary transmission modes, including face, mouth or nose touching, need to be avoided. Hygiene measures such as washing of hands and exposed surfaces are highly recommended.
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