As noted above, the 'fire load' is the real issue. That is, the stuff on board that burns. Same as in buildings. The interest in fire resistance of the structure has more to do with the safety of the occupants than in the structure itself. The time ratings given to structural components are for the amount of time you have to escape or to fight the fire. The ratings are determined by standard tests and thus may bear little resemblance to performance 'in the field' (maintenance, installation, etc.)
Fire safety has infinitely more to do with design and installation of components, maintenance, storage, care by the occupants than it does in the material of the structure.