[Lewis Thomson (OP)]

Alex needs some clarification on this scenario.

"If there's a roomful of people and 1 person has covid and there is a window open for "circulation" ..the person with Covid19 sneezes or coughs, the breeze coming through the window will or won't spread the virus around the room making contact with surfaces and the other people?"

Leave your help in the comments below...

[evan_au]

If an infected person breathes out (say) 1,000 virus particles per minute, and the office air conditioning keeps recirculating the same air for 4 hours, by lunchtime there will be something like a quarter million virus particles floating around - not very healthy air for someone else to breathe!

But if the window and door are open, and there are 5 air changes per hour*, after 4 hours there will be something like 5,000 virus particles floating around in the air. Not great, but much better!

Opening the window and door might be feasible when the outside temperature is ok; but if the outside temperature is far too hot or far too cold, people will be reluctant!

* I heard someone suggesting 5 air changes per hour. Apparently you can use a carbon dioxide monitor to assess whether there is enough air flow for the number of people...

[wolfekeeper]

You really want a through draft, an open door, and an open window for example.

But none of that will matter if the person isn't wearing at least a crude mask.

The reason is physics: when someone with Covid talks, sings, sneezes or coughs they emit a jet of air which carries virus particles long distances across the room. If you're in the way, you'll inhale it.

But if they're wearing a mask, then the jet gets stopped, and comes out of the sides of the mask relatively slowly.

Then, a second effect kicks in- humans are hotter than room temperature. That means there's a hot air plume rising from them all the time, and the covid gets carried up in that plume to the ceiling.

Once it reaches the ceiling, one of two things happens- either it cools back down and rains down on everyone in the room to be inhaled or it gets carried outside by the ventilation.

So you really want ventilation, such as a window to be open high up, and the door or another window or forced ventilation to be open low down to provide a through draft.

But it won't work nearly as well, unless everyone is wearing a mask.