The foam wasn't PUR, apparently, it was Celotex FR5000 PIR, so a bit less flammable, but still a source of flammable gasses as it broke down under heat.  From the photos, it looks like a lot of the charred PIR is still on the building, which suggests that the foam wasn't the primary fuel for the fire.  Also, looking at the flames when the tower was alight, there are clear signs that a lot of the external fire was probably the aluminium itself burning.  As aluminium burns at a very high temperatu