Also note that the averaging is based on the official working week, which to this day still runs from Monday to Saturday, i.e. six days, so anything up to 48 h/week remains fully within the 8 h/working day average.
3x12 on the other would be illegal on the other hand, unless it includes a significant amount of on-call duty or falls within one of the other permitted exceptions (which probably wouldn't apply to your co-worker, though).
If you work 10/12 hour shifts you have no life. No wonder people await the weekend like it’s air.
The thing to note is that the average is based on the official working week, which to this day still runs six days, Monday to Saturday. So as long as you're working less than 48 h/week, it's actually impossible to exceed the 8 h/average day limit and 3x10 h is perfectly fine from that point of view.
Extra pay and/or extra days off are only mandated for night-time work, anything else is a matter for wage agreements or your individual contract.