Familiar measures and adequate ventilation prevent airborne spread of coronavirus
Coronavirus is spread by droplets and fine aerosols. Both are expelled, when speaking, singing, and shouting, for example. The main difference between a droplet and an aerosol particle is their size. The largest droplets fall down quickly, but lighter aerosols hover in the air and can sometimes cover long distances over a long time following air movements.
The airborne spread of the coronavirus can be prevented through measures that are like those used against droplet transmission. Using a dense facemask is recommended especially in crowded indoor spaces. It is generally good to avoid large crowds, or at least to keep a distance to others, if many people congregate in the same space. It is also a good idea to limit the time spent in such places.
The airborne spread of coronavirus can also be prevented through ventilation.
“According to research, more efficient ventilation can reduce the risk of aerosol transmission, especially in small spaces with poor ventilation. In homes and in other spaces where people are constantly present, ventilation should be kept on without interruption”, says THL Senior Researcher Hanna Leppänen.
Coronavirus spreads by droplets, through the air, and by direct contact
In addition to droplets and aerosols, coronavirus can be spread directly through touch, for example, when an infectious person coughs in their hands and shakes the hand of another person, who then touches the mucous membranes of their own mouth, for example, allowing the virus to enter their body.
Larger-sized droplets contain more viruses than smaller aerosol particles, increasing the likelihood of infection. On the other hand, small-sized aerosols can be inhaled deeper into the respiratory tract, and exposure is possible anywhere in the space, while exposure to droplets only happens near the person who is infected.
“It is clear that no single means of fighting a disease is sufficient on its own to fight coronavirus infections; all means should be used – staying at home if symptoms are present, washing the hands, using a dense mask, avoiding crowds, limiting the time spent in spaces with other people outside one's own household, and increasing ventilation when needed”, Leppänen says.
“And most important of all is to take the coronavirus vaccine”, she adds.
THL publishes instructions on improving ventilation efficiency
THL has published instructions on its website on indoor ventilation during the coronavirus period. The instructions are directed at places such as schools and educational institutions, but they can be utilised by anybody.
Instructions have been published since May 2020 and they have been updated with the accumulation of new research information on the airborne spread of the coronavirus.
“By international comparison, Finnish buildings have efficient ventilation, but in some buildings, ventilation is not very good. The condition of ventilation is worth checking, and filters should be changed regularly to ensure that the ventilation is working properly”, Leppänen says.
If ventilation is inadequate, air purifiers can also help reduce the number of viruses in indoor air.
“According to research, mechanical filtration, or so-called HEPA filters, remove particulate impurities, which viruses are classified as. The effectiveness of ventilation can also be improved by using window ventilation, preferably for cross-draught, as often as possible, taking weather conditions into account.”
Further reading:
SlideShare presentation (in Finnish): Koronan ilmavälitteinen leviäminen ja sen torjuminen
Coronavirus and safety of indoor air
Further information:
Hanna Leppänen
Senior Researcher
tel. +358 29 524 6386
[email protected]
