Ventilation must be improved in buildings and aeroplanes to reduce the risk of covid-19 spreading via the air, according to recommendations from several organisations, including the European Union Aviation Safety Agency. However, it is unclear if this advice is being followed.
We know the coronavirus can spread via air, but there is still debate about the details and how much this form of transmission contributes to the disease鈥檚 spread. What is clear is that the risk is greatest if you spend a long time in a confined, poorly ventilated space with others who might be infected 鈥� something that many workers cannot avoid.
For this reason, scientists and safety experts think there should be more emphasis on improving ventilation, in addition to measures such as handwashing and social distancing. 鈥淭he most significant measure is to increase ventilation to remove the virus-laden droplets from the indoor environment where they were exhaled,鈥� says Lidia Morawska at the Queensland University of Technology in Australia, who thinks much more needs to be done to prevent the spread of covid-19 via air.
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When infected people cough, sneeze, shout, sing, talk or even just breathe, they emit droplets containing the coronavirus into the air. The closer you are to them, the more likely these droplets are to end up in your eyes, nose or mouth. This much everyone agrees on.
In January, 10 people from three different groups became infected after eating at a restaurant in Guangzhou, China. It is thought the air flow from an air conditioner blew droplets from an infected person to nearby tables.
And in March, a single person infected at least 32 of the 61 people at a choir practice in a small church in Washington state, according to a by the US Centers for Disease Control and Prevention. The choristers say they used hand sanitiser, didn鈥檛 touch and tried to maintain social distancing.
According to the World Health Organization, the coronavirus is carried by relatively large droplets that rapidly fall out of the air. The WHO calls this 鈥渄roplet transmission鈥�, and reserves the term 鈥渁irborne transmission鈥� for spread by droplets less than 5 micrometres in diameter that can remain in the air for long periods, forming an aerosol. Airborne transmission is possible, according to the WHO, but only when medical procedures, such as intubating a person to put them on a ventilator, generate aerosols.
Some researchers think this distinction is both confusing and wrong. 鈥淚t鈥檚 not helpful,鈥� says Linsey Marr at Virginia Tech. She says the virus-carrying droplets emitted by infected people range in size from microscopic ones to those large enough to be visible, with no clear dividing line. However, people emit thousands of times more smaller droplets than large ones, and she thinks these are what infect people.
鈥淚t鈥檚 airborne in that it is transmitted in microscopic droplets that are inhaled,鈥� says Marr.
When asked to comment, the WHO simply restated its position.
While microscopic droplets can travel further in the air than larger droplets, says Marr, their concentration falls off rapidly with distance, like exhaled cigarette smoke. Outdoors, people are unlikely to breathe in enough virus to infect them unless they remain close to an infected person for an extended period. Indoors, the risk is much higher.
There is plenty of evidence that the risk of getting infected is higher in confined spaces. For instance, one person in South Korea infected 94 of the 216 people .聽However, to what extent airborne spread contributes to such clusters remains unclear.
A from China does attribute coronavirus infections among bus passengers in Hunan province to airborne spread, with one person sitting 4.5 metres away from another passenger who infected them. It suggests the virus can remain airborne for at least 30 minutes.
Several studies have failed to detect the virus in the air near covid-19 patients, says Morawska. But these studies were done in medical facilities with good ventilation. 鈥淚f you remove the virus, you cannot find it,鈥� she says.
鈥淕iven the growing body of evidence suggesting airborne transmission may be a route of infection鈥� it is prudent to ensure ventilation is operating appropriately to protect occupants,鈥� said the UK鈥檚 Chartered Institution of Building Services Engineers (CIBSE) in guidance to its members.
Its recommendations include using only outside air if possible, rather than recirculating some of the air within buildings as is usually done. Where air has to be recirculated, HEPA filters or ultraviolet sterilisers could be used to eliminate any airborne virus.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers in the US has issued similar advice, as has the Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA) in Belgium.
So too has the European Union Aviation Safety Agency in Germany. Aircraft operators should either install and use HEPA filters, or avoid recirculating cabin air completely, according to the agency.
A spokesperson for Public Health England told 快猫短视频 it supports the REHVA and CIBSE guidance. However, these are recommendations only. It isn鈥檛 clear to what extent they are being implemented.
