[fireftr18]

It will be some time before the official cause is released to the public. I suspect the investigators will go through it very thoroughly and take a lot of time with it before reaching an official conclusion.

alboverburn, outside exit is a good thought. It's not done anymore because of issues with weather and maintenance. I can't speak for Britain, but I suspect it's similar to the US. The interior stair wells are isolated from rest of the building with a fire wall enclosure. Some buildings have pressurized stair wells. The hallways are supposed to be divided up with fire doors to limit smoke movement. If properly constructed, the stairwells and hallways should remain smoke free and safe. If not properly constructed, or if the safety features are over-ridden, they will not work as efficiently as designed. History shows it has tragic results.
I saw a layout of the building. It's what's called pedestal construction. There is a central supporting frame. Inside that frame is the stairwell, elevators and utility supply. The floor supports are attached to this, and often an auxiliary external frame. The external wall panels are what is called curtain walls. Very common with this type of construction. The panels simply hang from a framework and are there for waterproofing. As I understand, the panels were a composite of an insulating material and aluminum sheeting. Given how black the smoke was, I guess the insulation was petroleum based and not properly treated for fire proofing.