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I would also like to correct one of my previous references:
The office spreading example https://wwwnc.cdc.gov/eid/article/26/8/20-1274_article was more likely an example of extended contact time than of air crossflow, although both were likely involved. However, CFD outputs can be presented in such a way as to provide profiles of various calculated parameters, such as velocity, residence time within an area, and potentially "safe distance-risk zones", by correlating (a) virus shedding rates and (b) the necessary contact time at various concentrations of travelling viral particles, to present lines of constant "safe" contact time, e.g. only 1 minute is safe at X distance to the host, whereas 5 minutes or 15 minutes may be safe at Y distance.
The 2m distancing criterion will be ineffectual on tube trains where air flows are along the carriage at sometimes considerable velocity, especially when the carriage-end communicating door windows are open, as they will be in the approaching summer. Such an arrangement will virtually guarantee cross-infection of other passengers from a COVID host unless much greater distancing than 2m is adopted. These matters can be demonstrated using Computational Fluid Dynamics, such as was carried out for a supermarket scenario by Aalto University in Finland https://www.aalto.fi/en/news/researchers-modelling-the-spread-of-the-cor... , with the possibility therein of establishing realistic criteria and strict carriage loading limits.
Re: Covid-19: Return of Monday morning rush hour
Dear Editor,
Further to my Rapid Response yesterday, I would like to draw attention to the very Computational Fluid Dynamics work which I have been calling for.
This may be found at https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/artic... and demonstrates the value of the CFD modelling technique and its surrounding sciences in the fight against COVID-19.
I would also like to correct one of my previous references:
The office spreading example https://wwwnc.cdc.gov/eid/article/26/8/20-1274_article was more likely an example of extended contact time than of air crossflow, although both were likely involved. However, CFD outputs can be presented in such a way as to provide profiles of various calculated parameters, such as velocity, residence time within an area, and potentially "safe distance-risk zones", by correlating (a) virus shedding rates and (b) the necessary contact time at various concentrations of travelling viral particles, to present lines of constant "safe" contact time, e.g. only 1 minute is safe at X distance to the host, whereas 5 minutes or 15 minutes may be safe at Y distance.
Competing interests: No competing interests