Fire safety in wooden structures is interesting. A friend who does research in the area explained that, in some ways, wooden beams are simpler to engineer than steel beams when dealing with fire.

The goal, engineering wise, is to put a number on a given structure - how many hours can it burn before it falls?

A steel beam will maintain most of its strength up to the point it suddenly becomes soft and loses all of it. The exact point in time this occurs is hard to predict, because it varies substantially with several variables.

A wood beam will maintain the full strength of the beam, minus the average thickness of wood that is burned off per hour, which is a reasonably well known quantity.

This makes it simple (though not easy, of course!), relative to steel structures, to put a number on a wooden structure - "this building can burn for 2 hours before it is no longer safe for firemen to try to put it out from inside".