Publications
- Infected droplets released through sneezing can have a monumental effect on others, a new study shows
- The researchers used mathematical modelling to investigate how far large and smaller droplets can travel
- Based on their results, they can travel further than 3.5 metres, which is double the WHO's physical distancing recommendation
One of the most common ways the new coronavirus is known to spread is via close contact with infected people. When they breathe, speak, sing, cough, and sneeze, their saliva, respiratory secretions or secretion droplets are released from the mouth or nose, notes the World Health Organization (WHO).
According to WHO, if you are within one metre of an infected person, you risk being infected if those infectious droplets get into your body via your mouth, nose or eyes.
And with more evidence pointing to the virus being airborne (infected particles remaining suspended in the air after being exhaled), maintaining physical distancing is even more critical. But is one metre sufficient? According to a new study, it certainly isn’t.
To understand just how far these microparticles ejected by a sneeze can travel, scientists from Loughborough University in the UK created a mathematical model and put it to the test.
Their model revealed that exhaled droplets can travel more than 3.5 metres (without a face mask), suggesting the standard 1–2 metre physical distancing limit may therefore not be adequate to prevent direct transmission.
"In the majority of our analyses, the predictions made by our model suggest that the largest droplets consistently exceed the horizontal ranges of two metres from the source before settling to the ground," explained study co-author and mathematician, Emiliano Renzi.
Their results were published in the journal Physics of Fluids.
About the study
For their study, Renzi and student Adam Clarke modelled the fluid dynamics of expiratory clouds ejected during coughing and sneezing.
According to their findings, the largest droplets consistently travelled further than two metres.
This, they explained, is due to a theoretical phenomenon in physics called "buoyant vortex" – described as the turbulent motion of hot, dense air that we eject together with the droplets when we cough or sneeze.
“In some cases, the droplets are propelled in excess of 3.5 metres by the buoyant vortex, which acts like a mini atomic bomb,” said Renzi.
Smaller droplets reach heights greater than six metres
The model also shows how the smaller droplets are carried upwards by this mini-vortex and take just a few seconds to reach a height of four metres.
In some cases, the smallest droplets studied (with a diameter of 30 micrometres), which are more easily propelled by the turbulence of the moisture cloud, reached heights greater than six metres. These droplets then remained suspended in the air for the duration of the simulation.
“At these heights, building ventilation systems will interfere with the dynamics of the cloud and could become contaminated," said Renzi.
However, based on their analysis, tilting our head downward as we cough or sneeze significantly decreases the range for the majority of droplet sizes.
“We recommend behavioural and cultural changes in populations to direct coughs toward the ground, in addition to wearing face coverings, which could help mitigate the risk of short-range direct transmission of respiratory viruses,” the researchers advise.
The WHO also advises covering coughs and sneezes with a tissue or bent elbow at all times, and most importantly, avoiding crowded places, close-contact settings and confined and enclosed spaces with poor ventilation.
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