In a large well ventilated fire The bunker would not be efficiently cooled by the sea water adjacent to hull The biggest insulator against the hull is the coal itself . Think of a boiler takes a lot of tube "area" to transfer the fire's heat to the water Coal is burned to hot gas with is then circulated
Now think of the coal in the bunker. The cold hull could keep the coal near it cooler but coal is a much better insulator then steel
the net result is a kind of "coking furnace" where volatiles are driven off the lower temperature coal near the steel wall and consumed in the fire .
I understand this, and one point to probably discuss would be: If this fire was burning for several weeks before Titanic sailed as "experts" assume (I have never actually seen any proof of how long this fire was burning but maybe Sam or others has) and was so hot and hungry for fuel, wouldn't it be basically impossible for a few guys who are not professional firefighters, armed with some shovels, a few carts, and a water hose to extinguish the fire, wait for any residual volatile gasses/heat to dissipate, and then empty out presumably dozens of tons of coal or maybe hundreds in just a few days? They dont have protective/breathing equipment, probably very little/any training on how to supress fires, and very basic tools. The time frame just doesnt make sense unless the fire was tiny and easy to extinguish...