"I've never had that feeling in a basement."
I think that soley depends on the cleanliness of the basement in question...
Anyway, reguardless of basement, attic or crawl space, it is accessible, and exposed work, even if the client is not going to go in there... 334.15(A) says follow the surface of framing or running boards... (B)"shall be protected from physical damage where necessary..." So IMO, if it is an accessable basement, attic or crawl space, and you would know of it being accessable, seeing that you are in it, it could be subject to damage, or become a hazard for the next guy down the line. I think 334.15(B)+(C) would apply... If it is accessible it is exposed work...
In an attic type crawl space 320.23 would apply... As 334.23 would direct you there for "accessible attics or roof spaces"
So where is this "Crawl Space", above below or through the building?
"Well - I oughta....." -Jackie Gleason