Coronavirus particles from a cough linger in the air BEHIND an infected person in a corridor – posing an infection risk to children, study warns
- Researchers used computer models to see how space changes air flow
- Found close walls like in a corridor changes behaviour of particles from a cough
- In open space they latch on to the cougher’s back and form a ‘tail’
- But in a corridor they detach and create a ball of suspended particles several feet behind the person that can last for several seconds
Coronavirus particles expelled from a person’s uncovered mouth in a tight space like a corridor can linger at waist-height behind them for several seconds, a study warns.
The finding comes from computer simulations which show how particles behave after being coughed out by someone who is walking forward.
Swirling air and vortexes allow the particles to float in the air up to 16 feet (five metres) behind the infected person, posing significant problems for social distancing and increasing infection risk for children.
Pictured left: the detached mode created in a narrow corridor which sees a highly-concentrated mass of suspended coronavirus particles several feet behind an individual. Right: the same person walking at the same speed but in an open corridor. It shows an ‘attached’ form of circulation which sees particles stick to the person’s back and shoot out like a waist-high tail
Researchers from the Chinese Academy of Sciences in Beijing used a man of 1.8m (5ft 11in) walking at 1.5m/s (3.5mph) as an example.
They modelled what would happen if he coughed, without a face mask on, in both wide open spaces and also a narrow corridor.
Previous studies have focused almost exclusively on the spread of infectious particles in places with no confinements. This new study investigated how particle behaviour differs if they are physically penned.
They found that when walking in confined spaces, airborne droplets carrying the deadly virus follow a specific pattern, dubbed the ‘detached mode’.
Computer visualisation show particles are flung behind a person by the air currents made as they walk and a cloud of droplets separates from the body and forms a levitating blob of infectious aerosols several feet behind the individual.
This graphic shows what happens when a 5ft 11inch man walks at 1.5m/s and coughs in a corridor (left) and in an open space (right). For the latter, the particles are attached to the individuals back, and for the former they create a separate ball several metres behind
It is highly concentrated and is formed as a direct result of the walls buffeting and funnelling air in one direction.
However, in an open space, the researchers found virus-laden droplets from a cough follow a different course.
As air surges over a person’s shoulders and down their backs it also flows around their waist and up the back, with both streams meeting in the middle.
As a result of this, the particles produced by a cough in an open space get tangled in a ‘re-circulation bubble’.
The bulk of the particles sit here, but some also trail out behind the person as they walk, forming a long, thin and invisible tail of coronavirus particles.
The researchers say this so-called ‘attached mod’e puts children at particularly high risk of catching the virus in this manner as it is at an adult’s waist height but this is a child’s head height.
Professor Xiaolei Yang, author of the study, added: ‘The results reveal a higher transmission risk for children in some instances, such as behind quickly moving people in a long narrow hallway.’
‘For the detached mode, the droplet concentration is much higher than for the attached mode, five seconds after a cough.
‘This poses a great challenge in determining a safe social distance in places like a very narrow corridor, where a person may inhale viral droplets even if the patient is far in front of him or her.’
The findings were published in the journal Physics of Fluids.