https://www.erinbromage.com/post/the-risks-know-them-avoid-them

Commonality of outbreaks

The reason to highlight these different outbreaks is to show you the commonality
of outbreaks of COVID-19. All these infection events were indoors, with people
closely-spaced, with lots of talking, singing, or yelling. The main sources for
infection are home, workplace, public transport, social gatherings, and
restaurants. This accounts for 90% of all transmission events. In contrast,
outbreaks spread from shopping appear to be responsible for a small percentage
of traced infections.

Importantly, of the countries performing contact tracing properly, only a single
outbreak has been reported from an outdoor environment (less than 0.3% of traced
infections).

So back to the original thought of my post.

Indoor spaces, with limited air exchange or recycled air and lots of people, are
concerning from a transmission standpoint. We know that 60 people in a
volleyball court-sized room (choir) results in massive infections. Same
situation with the restaurant and the call center. Social distancing guidelines
don't hold in indoor spaces where you spend a lot of time, as people on the
opposite side of the room were infected.

The principle is viral exposure over an extended period of time. In all these
cases, people were exposed to the virus in the air for a prolonged period
(hours). Even if they were 50 feet away (choir or call center), even a low dose
of the virus in the air reaching them, over a sustained period, was enough to
cause infection and in some cases, death.

Social distancing rules are really to protect you with brief exposures or
outdoor exposures. In these situations there is not enough time to achieve the
infectious viral load when you are standing 6 feet apart or where wind and the
infinite outdoor space for viral dilution reduces viral load. The effects of
sunlight, heat, and humidity on viral survival, all serve to minimize the risk
to everyone when outside.

When assessing the risk of infection (via respiration) at the grocery store or
mall, you need to consider the volume of the air space (very large), the number
of people (restricted), how long people are spending in the store (workers - all
day; customers - an hour). Taken together, for a person shopping: the low
density, high air volume of the store, along with the restricted time you spend
in the store, means that the opportunity to receive an infectious dose is low.
But, for the store worker, the extended time they spend in the store provides a
greater opportunity to receive the infectious dose and therefore the job becomes
more risky.