You're obviously thinking of a well-designed (not to mention, well-maintained) system there, Neil.

Maybe I was unlucky, but I never came across many of those!

Actually, that reads like provisions made for Operating Theatres, and so forth. I don't think you'll find many (expensive) HEPA filters in nurses' accommodation. And fire protection will depend upon the "Code" being followed (zoning, sprinklers etc.).

PS: Have you ever taken a look inside HVAC ducts that have been operational for more than a year or two?

If you don't inspect ... don't expect.