The workers admitted it was dangerous, and came down from their 40' ladder. But, they didn't have an anchor point to tie off to, and had to wait for their supervisor. I happened to be there when the boss came. He was friendly, told me his plan to tie off to some eye-screws in the wall, talked about his and the workers' home country Brazil, and offered me some pizza. I declined.
I didn't have time to check up on them, but my mother walked by later and reported that they were back up on the ladder without a harness again. Kinda frustrating. Makes me wish I'd gotten a picture. I could have sent the picture to OSHA...
Turns out sending a picture wouldn't have done anything. Working 40' up on extension ladders isn't banned. According to this official interpretation and others, working without tie-off is okay on "portable ladders," even though it isn't allowed above 24' on permanent bolted-to-the-building "fixed ladders." What a confused and wimpy interpretation. If the fall protection system broke for a 40' high bolted-on ladder, like the ones on the cylindrical fuel storage tanks, then you could put a far less-stable extension ladder right next to it and do the same work without any fall protection!
I guess I would have to scour up some fatality statistics records and write some editorials if I wanted to follow through. Ultimately, it's a hole in the regulation.