Wearing a mask while coughing results in a “cloud” of droplets suspended in the air which is up to 23 times smaller than if a face covering is not used, a study has found.
Researchers discovered that the volume of a cough-cloud without a face mask was seven times larger compared to a surgical mask and 23 times larger compared with a N95 mask – the face coverings sometimes used by cyclists which are designed to block the smallest of airborne particles.
They also found that the cough-cloud was present in the air for five to eight seconds, after which the cloud starts dissipating, irrespective of the presence or absence of a mask.
Masks have become a central part of health advice from the World Health Organisation and governments worldwide to tackle the spread of coronavirus.
While there is a large body of evidence that supports their use, the team behind the latest study said the concept of droplets being dispersed in the surrounding air, and therefore the possibility of transmission, was still “poorly understood”.
“The role of air ejected during coughing and sneezing, and its subsequent mixing with the ambient air, is ... crucial in understanding the spread of the pandemic,” said authors Amit Agrawal and Rajneesh Bhardwaj.
“Our analysis suggests that the first five to eight seconds after the commencement of the cough event are crucial for suspending the exhaled droplets in air and the infected air volume is around 23 times more than that ejected by coughing.
“The presence of a mask drastically reduces this volume and consequently, significantly cutting down the risk of the infection to the other persons present in the room.
“Similarly, actions which drastically cut the distance travelled by the cloud, such as coughing into the elbow and use of a handkerchief, can reduce the volume of the cough cloud and therefore chances of dispersion of the virus.”
The researchers, from the Mumbai-based Indian Institute of Technology, said their study, published in the Physics of Fluids journal, could be used to help design ventilation of enclosed spaces to reduce the spread of the disease.
Their work could help in determining how many people could safely be accommodated in a hospital ward, train carriage, aircraft cabin or restaurant, for example.
Numerous studies have shown that wearing any type of face covering over the nose and mouth can help in reducing the spread of viral droplets when a person coughs or sneezes.
An international report published in The Lancet on 3 June, which analysed data from 172 studies in 16 countries, estimated that by wearing a face mask there was just a 3 per cent chance of catching Covid-19.
In July, UK scientists said that mask-wearing should be adhered to in all public places where it is hard to social distance, particularly in crowds.