@forth I use a mask any time the co2 level (as proxy for adequate ventilation) is over 700. so far I’ve avoided COVID at a number of events where others were infected. Having the co2 meter gives me a quantifiable level of comfort. I mask up on public transport, enclosed spaces, and anything like doctor or hospital areas. And I’ve largely avoided concerts and similar by-choice gathering.

@forth
I wear an n95 I'm likely to be in a place with more than ~5 people I dont know for >~15m, scaled by vibes on how well ventilated and dense the area is. I'll bop into the warehouse grocery store for 5m without a mask outside rush hours, but I'm wearing a mask tight and for the full time at any bar, concert, protest, etc.

(I know this will inevitably be imprecise and somewhat inaccurate. Even just now, I looked back at what I'd written and though, "An uncrowded semi-enclosed space might be preferable to a crowded outdoor space, depending on who is present and how windy it is.")