The best is to try them on and see how well they fit your particular face. But very roughly the bigger the distance between your chin and the bridge of your nose is the bigger a mask you need.
Aren't those less effective at protecting other people than using a mask without a valve?
Yes. On the other hand they have less condensation, are easier to breathe in, and are generally much easier to find in higher protection factors (I'm not aware of any valveless 99%+ efficacy masks)
I think cost much more than doubles: at the beginning of covid high-quality masks were essentially not available at all. If you imagine something like uncontained SARS I expect this would be even worse.
You're can substitute your own value for "what would I pay not to die", but unless your expected number of remaining life years is really low I doubt this changes much?
What was the rationale behind cleaning the air above people's heads - was eye safety the main concern for you?
To clean the air between the people you need UVC on the ceiling pointed down, and you need a lot of lamps. This isn't something we'd be able to set up in a hall we don't own. Additionally, the efficacy of UVC is proportional to the distance the rays traverse, so we're getting a lot more benefit from an emitter aimed above people than we would from downward facing ceiling-mounted ones.
Eye safety is something we're thinking about, but the risk is at close range. With all of the options we're considering the lamps are at least five feet from anyone's eyes, which is more than enough for safety.
Did you also do any prior modeling of the space before the setup?
We did a little modeling on the UV setup, yes!
when in the future would you expect that kind of data to be easily accessible from the NAObservatory website?
Sorry for being slow (this came out in June) but this data is now linked from our website for the treatment plants that have given permission: https://dholab.github.io/public_viz/001-make-by-city-and-by-virus-dashboards/index.html
1the two respirators I know of that do not were designed by amateurs during the COVID pandemic
I'm aware of at least the ElastoMaskPro, Flo Mask Pro, and Envo Pro N95. Are these what you're talking about?
almost all industrial respirators have valves
Sure, but they're also not designed for infection control. If you're using them in a situation where you don't need source control, then a valve is great. But ones designed for medical contexts generally don't have valves.
maybe my concern about evaporation vs making droplets is irrelevant
I think that's the case -- if you look at more recent work they've used a wide range of ways of getting glycol into the air.
I wonder whether fog machines that are already installed in crowd-gathering venues could be used for infection control!
It's more than that: fog machines used today (when used with glycols, which is the normal fog juice) are already performing infection control!
Are you planning any measurements of how far the TEG travels or how effectively the humidifier-generated droplets clean the air?
I'm not, though if anyone wanted to come test efficacy I'd be happy for them to measure the effect of us having it on sometimes and off other times.
it's possible that you were wearing well-insulated shoes
I was barefoot, but I'm also not sure shoes would be that big a component since I was fully in the water?
you just didn't notice the sensation because of adrenaline
I don't remember feeling any shock, and I think I still would have noticed?
The first one on this page, the ElastoMask Pro, filters bidirectionally. I have one and like it, very breathable, good deal. Though it's one of the worst for intelligibility.