Beside the type of steel, defining the dimensions, geometry and number of exposed sides is crucial for classifying the fire resistance of a particular building element, which are expressed by the profile cross-sectional factor fp = Fp/V (m-1 ). It describes the relationship between the effective volume of the profile exposed to fire (Fp) and the cross-sectional area of the profile (V).
Steel profiles with a higher cross-sectional factor, for example fp = 300 m-1 (large circumference and small cross-sectional area) have low fire resistance and therefore need a high level of fire protection, i.e. greater film thickness of the expanding coating to meet the required duration of fire protection.
Steel profiles with a smaller cross-sectional factor, for example fp = 160 m-1 (small circumference and large cross-sectional area), have higher fire resistance and therefore require less fire protection or less film thickness of the intumescent coating.