The point is that in typical apartment fire, the temperature rises to at least to 800C. Steel has good thermal conductivity, and therefore steel structures star

The point is that in typical apartment fire, the temperature rises to at least to 800C. Steel has good thermal conductivity, and therefore steel structures start to bend greatly when temperature hits 600C in a single floor. This usually causes a collapse. It's very important to quickly evacuate steel building if it's on fire. With massive wood structures the situation is different. The wood is very good heat insulator, so if the skin gets to 1000C the inside might still be lot less than 250C. Wood doesn't burn that quickly as it has to evaporate first (we usually call this smoke) before it can burn. Of course this is all dependent of scale. If you try this out at your fireplace with something that fit's there, the story is completely different. My info comes from Helsinki university of technology construction material lectures. So I can't really paste sources here.