It's a little more difficult than just "ambers which were put out once they got to that part of the coal starage". These coal bin fires were not uncommon however they were nothing short of very hard to contain.
These pockets of spontanious combustioned coal were oftain deep into the bin and low to the bottom near damp floors, which meant many may burn for days before discovery and even then these coal bin fires were usually commomplace and left to extinguish on there own.
One unknown factor is the reaction to the steel's compounds to intense heat and the cold steel which was cooled by the steel conduction from the frigid ocean's 32 degree waters. It has been debated that this cold/hot reaction could weaken or could cause a more brittle characteristic unknown factor.
There are many threads already posted on this topic and are worth ready. However you are on the right trail I believe myself that the coal bin fires are just a red herring.