Smoke and heated air and/or asphyxiating gases are responsible for about 75% of fatalities in house fires. A steel frame will not burn. It will not therefore contribute to the fire or its spreading, and will not release smoke and carbon dioxide. Electrical faults cause many fires in wall cavities. An electrical fault cannot ignite a steel frame. If fire gets into the ceiling and ignites timber trusses it can spread very rapidly to the rest of the house. In a bushfire the point of ignition is often the roof cavity when burning embers are blown in under the eaves or tiles. House fires have been known to break through ceilings into the roof cavity. A steel roof truss cannot be ignited in either of these ways.