The load-bearing capacity of corrugated steel without fire protection is 15-30 minutes depending on the structure. The steel is bending in case of fire but the load-bearing capability remains for quite a long time.

When there is no insulation used on top of the corrugated steel board, the heat goes through the metal and dissipates upwards and the steel temperature rises slower.

When corrugated steel is used as a load-bearing structure for the roof construction and insulation is installed on top of the corrugated steel board, the temperature of the metal is rising very quickly. This is why the insulation amount above the corrugated steel board has to be taken into account when designing the fire protection thickness below the corrugated steel construction.