I once did 3-12 hour shifts waiting for a boiler to be shut down so we could change out a relief valve.
The crew was 12 guys. I was on nights and there was also a day crew that worked 12's.
When the boiler was finally shut down in the middle of our 3rd shift, it took us 3 hours to remove, replace, and run all the tests we needed to pass inspection. The tests took two hours.
So in 36 hours, I worked for one. 12 of those hours were double time.
The whole crew slept on the roof of the boilerhouse for most of the job.
I have no idea what the bill was, but we were told that the downtime cost the company well over a million an hour. Anything they paid us for immediate response was well worth it.