Yes, helium costs would be a problem for large-scale use of airships. Yes, it's possible to use hydrogen in airships safely. This has been noted by many people.
Hydrogen has some properties that make it relatively safe:
and some properties that make it less safe:
Regardless, the FAA does not allow using hydrogen in airships, and I don't expect that to change soon. Especially since accidents still happen despite the small number of airships.
In any case, the only uses of airships that are plausibly economical today are: advertising and luxury yachts for the wealthy. Are those things that you care about working towards?
IKEA already sells air purifiers; their models just have a very low flow rate. There are several companies selling various kinds of air purifiers, including multiples ones with proprietary filters.
What all this says to me is, the problem isn't just the overall market size.
Apart from potential harms of far-UVC, it's good to remove particulate pollution anyway. Is it possible that "quiet air filters" is an easier problem to solve?
I'm not convinced that far-UVC is safe enough around humans to be a good idea. It's strongly absorbed by proteins so it doesn't penetrate much, but:
And really, what's the point? Why not just have fans sending air to (cheap) mercury vapor lamps in a contained area where they won't hit people or plastics?
As you were writing that, did you consider why chlorhexidine might cause hearing damage?
https://en.wikipedia.org/wiki/Chlorhexidine#Side_effects
It can also obviously break down to 4-chloroaniline and hexamethylenediamine. Which are rather bad. This was not considered in the FDA's evaluation of it.
If you just want to make the tooth surface more negatively charged...a salt of poly(acrylic acid) seems better for that. And I think some toothpastes have that.
EDTA in toothpaste? It chelates iron and calcium. Binding iron can prevent degradation during storage, so a little bit is often added.
Are you talking about adding a lot more? For what purpose? In situations where you can chelate iron to prevent bacterial growth, you can also just kill bacteria with surfactants. Maybe breaking up certain biofilms held together by Ca? EDTA doesn't seem very effective for that for teeth, but also, chelating agents that could strip Ca from biofilms would also strip Ca from teeth. IIRC, high EDTA concentration was found to cause significant amounts of erosion.
I wouldn't want to eat a lot of EDTA, anyway. Iminodisuccinate seems less likely to have problematic metabolites.
On the other hand, the hydrogen pushing against the airship membrane is also an electrostatic force.