(Throwaway, for obvious reasons.)

Yes, you can just build a wall or a door, even in the USA. I've done it. It may not be according to code, but that's the very issue here: enforcement. Until someone dies, how do they know? Surprise inspections are exceptionally rare. There's just way too many buildings.

I've even had modifications "inspected" by the fire department, multiple times. I put that in quotes because I've only ever seen them count the number of automatic sprinklers in the building (which did not change), or look to see if we had fire extinguisher signs, and a fire extinguisher under each one.

I've even seen the FD (in a modern American city) respond to and put out an actual fire, and not care that the building did not match the permit plans.

I'm curious what your experience is, as there is no aspect of this which I would describe as "heavily enforced".

That’s how it is. When there is a fire however and people get suffocated because of those modifications you did or just because it was a fire. Then you are in for some serious trouble if the changes can be traced back to you. Some jail time possibly, but the litigation from victims and insurance companies is what really is gonna do you in. Possibly also the guilt.

Don’t do it. Those plans and codes are there for a reason.

All of that other than punitive damages also applies in Poland. Yet until the Fire happened plenty of places locked the doors.

Maybe it depends on the city. In the towns I've lived in, it's been pretty strict.

But then again I was a firefighter, so if I see a code violation I'll call the fire marshal. I expect other firefighters would do the same, off duty or not.

Might this not deter someone violating the code from contacting the fire department in a timely manner in an emergency?

So....literally the same as in Poland then. That's heavy enforcement?

As a Canadian, I'm always somewhat amused how fire code is strictly enforced at events in the US. I've often seen inspections during conferences. US and UK have a much stronger fire code safety culture than elsewhere (although, as most things in the US, it can vary greatly between the big cities and more rural areas, including suburbs or sprawled cities like SF).

SF isn’t really a sprawled city by American standards. The cities outside of SF are sprawled (like San Jose) but SF is pretty compact in comparison.

Good examples of sprawled cities include LA and Houston.

I don’t know anything about Europe, but most escape room owners in the US can report multiple visits by the Fire Marshall. (I just got back from the national conference and talked to a lot of them.) It varies by municipality, but most places in the US pay more attention to escape rooms than the average business. They’re probably more safe than the office suite next door to which nobody pays attention.