Actually, the first metal frame (iron, IIRC) had a bad problem with quickly collapsing in fires that would not have brought down a timber frame building for a while. The very thick timber beams, girders and columns would char on the outside, but it took some time for the interior wood to burn & loose strength.
However, the iron would crack from thermal stresses or the steel would warp fairly soon. In many cases, current buildings are required by code to have insulation over the metal frame members. What sort of insulation?
Sprayed on wood fiber pulp and clay mix is one method.
Seems I recall something about absence of asbestos in the WTC towers.
As far as construction materials and fire safety, though, the combination of concrete and steel was marketed as being almost fireproof and they were by comparison to wood framed structures butted side by side.