CAMBRIDGE, United Kingdom — Although the “six-foot rule” has been a staple of coronavirus safety measure since 2020, is it really doing anything to keep people healthy? A new study finds the answer to that appears to be a resounding no. Scientists from the University of Cambridge say the social distancing rule of six feet does not protect against catching COVID-19, even outdoors.
The team calls the social distancing rule an “arbitrary measurement” of safety in the absence of masks. It could have been set anywhere between three to 10 feet, depending on the risk tolerance of the local public health authority putting out the mandate.
Infected individuals spread the virus through coughing, speaking, and even breathing. People expel larger droplets that eventually settle on surfaces or break into smaller aerosols that may float through the air. The study used computer modelling to quantify how these infectious particles travel. Results show coughs vary widely when it comes to expelling particles.
“I remember hearing lots about how COVID-19 was spreading via door handles in early 2020, and I thought to myself if that were the case, then the virus must leave an infected person and land on the surface or disperse in the air through fluid mechanical processes,” says lead author Professor Epaminondas Mastorakos in a university release.
No masks lead to an unknown dynamic when coughing
Scientists say the findings in the Physics of Fluids underline the continued importance of vaccination, ventilation, and masks heading into winter.
Early in the pandemic, health experts focused on hand washing and surface cleaning. However, Cambridge engineers note it’s been clear for nearly two years that COVID spreads through airborne transmission. They have developed various programs to investigate how the virus behaves in different environments.
“One part of the way that this disease spreads is virology: how much virus you have in your body, how many viral particles you expel when you speak or cough,” adds first author Dr. Shrey Trivedi. “But another part of it is fluid mechanics: what happens to the droplets once they’re expelled, which is where we come in. As fluid mechanics specialists, we’re like the bridge from virology of the emitter to the virology of the receiver and we can help with risk assessment.”
Simulations showed how much of the virus would reach another person in the same room from a cough containing 1,000 droplets. The researchers found there isn’t a sharp cut-off once the droplets spread beyond two meters.
When a person coughs and isn’t wearing a mask, most of the larger droplets will fall on nearby surfaces, but smaller droplets suspended in the air can quickly and easily spread well beyond the six-foot mark. How far and how quickly these aerosols spread will depend on the quality of ventilation in a room. In addition to the variables surrounding mask-wearing and ventilation, there’s also a high degree of variability.
“Each time we cough, we may emit a different amount of liquid, so if a person is infected with COVID-19, they could be emitting lots of virus particles or very few, and because of the turbulence they spread differently for every cough,” Trivedi continues.
The 6-foot rule may only be good for COVID messaging
The team’s calculations took into account turbulent flow and detailed descriptions of droplet motion and evaporation.
“Even if I expel the same number of droplets every time I cough, because the flow is turbulent, there are fluctuations,” Mastorakos says. “If I’m coughing, fluctuations in velocity, temperature and humidity mean that the amount someone gets at the two-meter mark can be very different each time.”
The six-foot rule is an effective and easy-to-remember message for the public. However, the study finds it isn’t a mark of safety given the large number of variables associated with an airborne virus. Vaccination, ventilation, and masks – while not 100 percent effective – are vital for containing the pandemic.
“We’re all desperate to see the back of this pandemic, but we strongly recommend that people keep wearing masks in indoor spaces such as offices, classrooms and shops,” Mastorakos concludes. “There’s no good reason to expose yourself to this risk as long as the virus is with us.”
The researchers are carrying out similar simulations for spaces such as lecture rooms to assess the risk as people spend more time indoors. The World Health Organization recommends a distance of at least three feet (one meter) from others — even if they don’t appear to be sick. WHO also advises people to avoid crowds and close contact and to wear a properly fitted mask in poorly ventilated rooms.
South West News Service writer Mark Waghorn contributed to this report.