Although I share the reservations of many about the use of windows as an escape route, I think it is naive and unworkable to rely on FR doors and construction to protect occupants on upper floors.
I recently converted my loft and the LA building control team were very stringent about AFD/an escape window/SC fire doors/FR material around steels etc.
Where they were sadly lacking was the smoke stopping between floors. My loft, in common with 1000's of other homes has lots of pipework entering the loft space from below. There was no inspection, supervision or recommendations about smoke stopping around these services.
The result could have been (if I hadn't acted on my own iniative and installed suitable FR material) a fire downstairs would be held back by a three ton fire door to the loft room, but smoke would spread quite freely via holes where plumbing enters the loft into under-eaves cupboards.
I know, in theory, it would be detected by the AFD system allowing escape, but with self closers on all doors, the smoke from a fire in a room may have trouble reaching the heads in the hall, whilst little difficulty finding the gaps to the loft.
In those circumstances, maybe a window isn't such a bad 'fallback' arrangement.