LOUGHBOROUGH, United Kingdom — While social distancing may be the law of the land during the coronavirus pandemic, is six feet really the magic number to keep you safe? Researchers in the United Kingdom say the power of a sneeze or a cough can carry germs far beyond six feet. Their study finds droplets from an unprotected sneeze can act like a “mini atomic bomb” and travel twice as far as social distancing requires.
A team from Loughborough University created a mathematical model to show what happens when people let loose with a cough or sneeze in the open air. Their findings reveal potentially infectious droplets regularly reach over 11 feet (3.5 meters) away without a face mask.
Dr. Emiliano Renzi and student Adam Clarke collected data in the researcher’s home while labs stayed closed during COVID lockdowns. Dr. Renzi says the largest droplets from sneezing consistently landed over six feet away from the origin point.
A vortex of germs
Study authors say this long-distance problem results from the “buoyant vortex,” a turbulent motion of hot and dense air ejected during a cough or sneeze. Making things worse, researchers suggest the range of droplets can be altered significantly depending on how someone tilts their head.
“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,” Dr. Renzi says in a university release. “In some cases, the droplets are propelled in excess of 3.5 meters by the buoyant vortex, which acts like a mini atomic bomb.”
Renzi adds that the current guidelines promoting social distancing of six feet may not be enough to stop virus transmission.
“Our model also shows that the smaller droplets are carried upwards by this mini-vortex and take a few seconds to reach a height of four meters,” Renzi explains. “At these heights, building ventilation systems will interfere with the dynamics of the cloud and could become contaminated.”
Have to sneeze? Look down fast!
Researchers say there is something everyone can do to help control this threat. Their study finds tilting your down when you cough or sneeze can drastically cut the range droplets travel.
“We recommend behavioral 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,” Renzi concludes.
The study appears in the journal Physics of Fluids.