I think it also depends if the pit is mainly for inspection or repairs. Also a drop pit section will have an influence on pit depth

If the pit is too deep or the worker too short, he can stand on something to reach the higher parts of the equipment.

It isn't unknown to have pits of varying depths depending on tasks. I'd expect people will want to carefully consider their needs before starting to dig - or stopping digging, depending. Just digging without knowing how deep and why is about the only real mistake possible.

dave