@Glennn,
You are confusing a forced-air-forge with a bloomery or a smelting furnace. A forge is just a bed of burning charcoal, semi-enclosed. It cannot melt iron because it's only semi-enclosed: there is a wide enough orifice to introduce stuff, and air is pumped in the system. I would guess it reaches about 1000 C. It's used to FORGE iron, not to melt it. It can make iron all red and maleable, but not melt it.
The principle of a smelting furnace is different: it is to enclose quite well, almost totally in fact, a heap of slowly flammable material eg charcoal mixed with iron ore. And then lit the fire. The fire NEEDS to be starved of oxygen because the iron itself is in an oxydated form in the ore, and you want to remove the oxygen from the pure metal. So less O2 pumped in the fire is actually better, in a smelting furnace. Carbon monoxide is the reducing agent of choice for smelting. It is easily produced during the heating process with limitted O2 supply, and as a gas comes into intimate contact with the ore. The point is that you don't need to force air in the system for it to reach 1500 C, the temp that melts iron. A slow burn will reach the same temp as a fast burn, only slower.
Your argument on the north tower does not apply to the south tower (where the fire was at mid heigth), so it's moot. The south tower alone explains the presence of a fire deep into the rubble pile.
