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.
This has me thinking about my own work and when we might return to open planned office space. Although we do not hot desk, it would seem that time and space are key ingredients to spread. No matter what strategies are put in place (one person in the lift, hand sanitiser units, limit to the size of meetings) it would seem that spread is somewhat inevitable given the right conditions?