Reading the news, I have been struck by how important “viral load” seems to be for the novel coronavirus. Being exposed to a large quantity of the virus seems to be much more dangerous than being exposed to a small quantity of the virus. The two big consequences of this are (a) how long one is near other people matters a lot and (b) it matters whether one has good ventilation—as is typical outdoors—or bad ventilation—as is typical indoors. To put a point on it: if you can help it, don’t spend a lot of time indoors with other people from outside your bubble; and if you have to, use a mask, distance yourself and make efforts to get better ventilation. For example, if you have to fly, you can put the air vent on at full blast and point it straight at yourself. (Airplanes tend to have high quality HEPA air filters.)

Caitlin McCabe, in the article shown above, “Key to Preventing Covid-19 Indoors: Ventilation,” lays out some key details. (All the quotations below are from that article.) Experts are beginning to emphasize the importance of good ventilation:

After urging steps like handwashing, masking and social distancing, researchers say proper ventilation indoors should join the list of necessary measures.

Contrary to the way many people are acting, being far away from someone isn’t good enough if you are with them indoors with bad ventilation for a long time:

Driving the thinking is mounting evidence that the new coronavirus is transmitted through the air among people with prolonged exposure to the pathogen. Especially troublesome, epidemiologists and other scientists say, is evidence from numerous indoor outbreaks suggesting the virus’s ability to spread to others even when close contact is avoided.

What counts as good ventilation? Turning over the air in a room something like six times every hour:

Ideally, they say, public spaces like a standard classroom should aim to have air replaced with clean air between four to six times an hour to dilute Covid-19 particles that might accumulate.

Common-sense measures can improve ventilation:

[Increasing the rate of air turnover] can be done, aerosol scientists and building engineers say, through strategies that introduce outdoor air and filter indoor contaminants. Those include opening windows and doors, installing window fans, using portable air purifiers with high-efficiency particulate air, or HEPA, filters and upgrading heating, ventilation and air-conditioning systems …

Unfortunately, many school rooms, for example, have air turnover only about once or twice an hour.

Note also that because indoor restaurants and bars are a hard place to use masks as well as often having quite poor ventilation, and often being quite crowded, they are a perfect storm for Covid-19 transmission. And indoor parties are often a lot like indoor restaurants and bars. If you are going to do a party during this pandemic, do an outdoor party!