Temperature monitoring, disinfectant gels, masks, sanitation crews wiping surfaces in public spaces, city portals with disinfectant sprays, and footwear cleaning mats—are all part of the hygiene-theater meant to combat the spread of the pandemic. But one measure is hardly spoken of—ventilation.
The coronavirus attacks our respiratory tract, is emitted through droplets when we breathe, talk, sing, cough, or sneeze. This is considered the primary mode of transmission, hence the emphasis on protecting our mouth, nose, and eyes. It is also the reason for social distancing, since droplets can only travel so far. Of course, we can pick up the virus from surfaces touched by someone infected, a reason for frequent hand washing; but the primary means of infection is through droplets. However, little has been said about the air we breathe, perhaps more important than the constant cleaning of surfaces.
Not all “airborne” transmissions are the same, some (like measles) can rapidly spread to every corner of a house; but the coronavirus doesn’t seem to be as highly infectious. Except when it runs amuck in “super-spreader” events—gatherings with many people talking, chanting or singing—indoor restaurants, bars, clubs, choir practices, weddings, funerals, and cruise ships.
Studies demonstrate that infections are more likely to take place indoors. In a study of 1,200 events both indoors and out, only one person was infected outside, while hundreds were infected indoors. The virus likes crowded, poorly ventilated interior spaces—it stalks us indoors. More health-care workers in the UK—where hospitals are older and ventilation poorer—became sick than those in the US, where many hospital buildings have better ventilation. Vocalization is another aspect of viral transmission. People emit different amounts of aerosols depending on activity: singing more than talking, shouting more than soft speech. Televised indoor events show audience members sitting distanced and masked, listening to a speaker or singer, who is unmasked. This is completely backward—the person who needs to be masked (or remain behind a filtering screen) is the one addressing the audience, not the listeners.
We ought to have different rules for the indoors and the outdoors, not only because of the diluting power of air but because sunlight deactivates viruses. Masks are needed indoors regardless of distancing, but not necessarily outdoors. Why should the solitary person walking a dog have to mask up? What sense does it make to close down beaches but allow gyms and restaurants to open?
The importance of aerosol spread indoors may even help explain why the disease is now exploding in the southern United States, where people often go into air-conditioned spaces to avoid the sweltering heat. But outdated air conditioning systems may be ineffective protection against the coronavirus, unless the filters are upgraded to HVAC systems or use portable HEPA filters. Otherwise, it is simply circulating the virus everywhere.
A key mitigation strategy to counter poor ventilation and virus-laden aerosols indoors is to introduce air from outside by opening doors and windows. This improves air circulation and dilutes any viral particles present. To speed the flow of air from the outdoors, you can place a fan in front of a window and blast it outwards. Any amount of air leaving a room will be replaced by the same amount of air from outside—it’s a fixed volume. Another healthy option is to stay outdoors as much as possible.
(Excerpt of: We Need to Talk About Ventilation, from The Atlantic magazine, 7/20/20)