I don't know much about hypochlorous acid fogging; it sounds like it would be corrosive, and probably at least somewhat bad for people?

For air pollution yes, but far-UVC should still work on mold.

Glycol vapors are generally going to be cheaper, but they're less far along. There isn't a product you can buy that will maintain your space at the right concentration. The closest you can get would be Bleu Garde (formerly Grignard Pure) but they're not actually selling their product.

I'd recommend playing around with Illuminate. Depending on the room size and shape, far-UVC can range from mildly less effective as a good air purifier on high to far more effective.

For example, lets say you have an Aerolamp in the corner of a tiny room (10ft x 7ft x 8ft). You'd need to dim the lamp to 70% to protect people who are near the corner. Illuminate calculates (guv) a CADR-equivalent for a range of pathogens, and taking the median I get 216 CFM. Then let's say you instead put it in a cavernous room (50ft x 50ft x 50ft). Now you can easily run it on full power (guv) and I get a median CADR-UV of 1,979 CFM. Even if you run it at 70% power to keep it apples-to-apples the median CADR-UV is still 1,354 CFM. (sheet) Of course most rooms will be well between these two extremes!

Compare to the AirFanta 3Pro at 413 CFM on high (though it's noisy enough on high that I only run mine that high if I need to clear smoke).

there's a cluster of advice I get from folksinger people that... seems totally "correct", but, feels... insufficiently ambitious or something. 

The advice includes things like "try to have people come in singing on the chorus, and not worry so much about the verses". Or "teach people the song beforehand" and "hold practice singalongs before the event or send out music so people can learn it", or "teach people music."

My guess is that the problem is if you're getting advice from people who are in communities where it's uncommon to get large groups of people we're singing is not central to their identity unfamiliar songs. So they don't have a very relevant advice! Instead I would look for material aimed at religious leaders, camp counselors, and teachers. (But I have no idea if there is good advice out there, or if this is one of the many categories where the people who are good at it have not passed on their wisdom, and in many cases don't even realize there could add it.)

try to have people come in singing on the chorus, and not worry so much about the verses

I think this is just massively obsolete, and dates back to people singing along without being able to read lyrics. Either because you didn't have printing, or people weren't (sufficiently) literate.

(Though there are also communities that intentionally don't involve written words in there folk singing, such as pub singers, which I do think can be a nice aesthetic. If that's what you're doing, then the format where someone sings the versus solo and everyone joins in on the chorus works well.)

On the 2012 Solstice, I do expect you had more people who enjoy this kind of singing. For example, @juliawise and I are both reasonably strong singers (including being comfortable picking things up on the fly) and I think a big part of why we were excited to come down from Boston was that the event involved singing. But I don't remember what fraction of the people that would have applied to.

I'm sorry, it's not up anymore. The code is still available if you wanted to host it, but part of why I took it down is that it depends on a Twilio video chat API that they've discontinued, so you would need to find some replacement for that.

How many people do you think this is each day? If it's 1,000 (train runs through busy areas, but most people don't cross tracks illegally) then the annual cost is ~3.7M minutes.

The the average person killed by a train would have had maybe another ~12M waking minutes [1], so fences that prevented even a death every three years would do more good than harm. And the number of tracks-crossers would have to be super high for fencing not to be worth it.

(But adding signaled crossings or overpasses could be worth it!)

[1] 60 min / hr * 16 waking hr / day * 365 day / year * 35 years

this is (slightly) better for humankind in the long run

We don't have to get into this here if you don't want to, but flagging that I'm not convinced of this.

It isn't quite an apples-to-apples comparison ... do worse by a factor of about 10

Thanks for looking into this! I am pretty skeptical of studies that don't explicitly compare the two options, because there are really quite a lot of variables that can go into measuring absolute effectiveness that are nicely factored out when you measure relative effectiveness.

The way it's supposed to work is that going from n95 to n100 should get you from 95% to 99.97% on the worst performing non-oilborne particle size, and then n100 to p100 would get you coverage for oilborne (which we don't expect to need for a pandemic, but is useful in industry). But I haven't looked into studies to verify that it does actually work that way in practice.