Oh yeah up to 16 hours. My friend worked in security and after a 12 hour shift he had to work another 8 hours before he was able to be relieved. Terrible.

To the best of my knowledge, there is no legal limit to how long I can remain at work. Even worse, I'm salaried so I don't ever get paid for it. I've done 24 hours twice - though one of those times was because it was during a snow storm and the governor declared a state of emergency, making it illegal for non-essential traffic; so I legally couldn't leave, and the next shift couldn't come in. I did get compensated with double-time flex time for that instance, at least.

Some places require workers to work 16 hour days here in the U.S.

Yes. Usually in the UK you are limited to a 48hr week unless you opt out of the working time directive. I may have to work 16hr days on occasions, and doctors and nurses work some ridiculous hours.

Up to 16

Only temporarily if there's some urgent work to do. It is stated that there must be an extraordinary reason for that. And then you have to have at least 8-hour break before another shift.

You can never go home for all most places care. As long as they don't have to pay you.

I’m salary
They’ll let me work as much as possible but still only get paid for 8 hour days

Yea. That’s the maximum
Unless you want to work more

I've worked double shifts

Yes I do it all the time

Yeah but I'm not gonna

If you want to, yes.

Yes.