2m social distance may be too close as coughs can propel saliva much further

Standing 2m apart may not be enough to protect people against contracting the coronavirus outdoors, according to new US research which suggests saliva particles can travel around three times that far when someone coughs – even in a light wind.

Scientists at the American Institute of Physics say the distance saliva can cross varies depending on environmental conditions such as wind speed, temperature, pressure and humidity.

They have also warned that children could be at greater risk of exposure to airborne particles because of their smaller size.

The conclusions, which are at odds with advice based on other scientific research, come after fluid dynamics simulations showed droplets expelled through coughing can cover nearly 6m in five seconds in a breeze of just 2.5mph.

Dimitris Drikakis, who carried out the work with colleague Talib Dbouk, said: “The droplet cloud will affect both adults and children of different heights.

“Shorter adults and children could be at higher risk if they are located within the trajectory of the travelling saliva droplets.”

Airborne transmission of viruses such as Covid-19 is not well understood, but the researchers believe their findings provide important evidence of how saliva particles can travel through the air when people cough.

“This work is vital because it concerns health and safety distance guidelines, advances the understanding of spreading and transmission of airborne diseases and helps form precautionary measures based on scientific results,” Mr Drikakis said.

He says further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air.