WORRYING tests have revealed that the two-metre rule isn't enough to stop Covid-19 spreading.
People in the UK have been told to follow social distancing guidance by keeping more than two metres (6ft) apart from anyone they don't live with amid the coronavirus pandemic.
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However, researchers have now discovered that those guidelines may be insufficient – because a mild cough occurring in low wind speeds can propel droplets of the deadly virus a staggering 18ft away.
It comes as the Government is examining whether the Government is examining whether the two-metre rule should be scrapped to allow more schools and businesses to reopen.
Researchers Talib Dbouk and Dimitris Drikakis created a simulation to gain a deeper understanding of how particles travel through the air when people cough.
And they found that with even a slight breeze of 4 kph, saliva travels 18 feet in 5 seconds.
Airborne transmission
Writing in a paper published in Physics of Fluids, from AIP Publishing, Drikakis 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 traveling saliva droplets."
Saliva is a complex fluid, and it travels suspended in a bulk of surrounding air released by a cough.
Many factors affect how saliva droplets travel, including the size and number of droplets, how they interact with one another and the surrounding air as they disperse and evaporate, how heat and mass are transferred, and the humidity and temperature of the surrounding air.
The droplet cloud will affect both adults and children of different heights
To study how saliva moves through air, Dbouk and Drikakis created a computational fluid dynamics simulation that examines the state of every saliva droplet moving through the air in front of a coughing person.
Their simulation considered the effects of humidity, dispersion force, interactions of molecules of saliva and air, and how the droplets change from liquid to vapour and evaporate.
The computational domain in the simulation is a grid representing the space in front of a coughing person.
The analysis involved running partial differential equations on 1,008 saliva droplets and solving approximately 3.7 million equations in total.
"Each cell holds information about variables like pressure, fluid velocity, temperature, droplet mass, droplet position, etc.," Dbouk said.
"The purpose of the mathematical modelling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves."
Further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air and to examine indoor environments, where air conditioning significantly affects the particle movement through air.
"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," said Drikakis.
This work is vital, because it concerns health and safety distance guidelines
Dr Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading, said that this
new study shows the importance of sticking to the two-metre rule.
He said: "This is a reminder that the two-metre rule is recommended, not because staying two-metres away from all other people provides you with a force field against infection, but because it is a reasonable distance to stay away from people to reduce risk of infection.
"While two-metres is better than one metre, ten metres or 100 metres is even better, although the protective effect is not proportional to the distance.
“The most important point to take away from this paper is not that we need to change guidelines on social distancing, but that coughing is one of the best ways to spread infected droplets if you’re ill.
'Protective effect'
"So if you have a cough, stay at home until you’re better – and if you cough unexpectedly when you are out and about, cough into your elbow. Then go home, and stay there."
Despite the new research, scientists say that being outdoors is generally lower risk when it comes to catching coronavirus.
Individuals in England are now allowed to meet with one other person from outside their household if they stay outdoor and keeping more than two metres apart.
However, the UK is reportedly the "only country in Europe" using the measure, with Germany using 1.5 metres and France and Italy using only one metre.
And the advice from the World Health Organisation (WHO) is that people should "maintain at least one metre (3 feet) distance between yourself and others."
Earlier today, former Conservative Party leader Iain Duncan Smith called on the Prime Minister to reconsider the two-metre social distancing rule to "get the economy moving".
He told BBC Radio 4's Today Programme: "We're the only country certainly in Europe that I know of that uses the two-metre rule.
"I think when it comes to the hospitality sector, I think we do need to look at it very carefully.
Easing of restrictions
"So we do need to look at how they manage that process and give them some flexibility."
The Government is said to be examining a number of possibilities for the eventual easing of coronavirus restrictions – including scrapping the two-metre rule.
As the Cabinet preps for an exit strategy, the Scientific Advisory Group for Emergencies (Sage) is said to have been asked to review if people do need to stay two metres apart.
One minister told the Telegraph: "We want to get the country back to work and we want to keep probing so we are not missing any opportunities.
"[Ministers have] asked Sage to get us further and better particulars as to how hard and fast that really is. It is important to understand how much reliance has to be placed on it.
“The response genuinely has been led by the science. It is just about understanding exactly what is required and what isn’t.
“This is not about weakening the rules but it is about trying to test if it is actually necessary to be two metres. What is the empirical evidence on this?"
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