Steel Buildings in Europe

Part 6: Fire Engineering 6 - 17 Sprayed non-reactive coatings are mainly cement or gypsum based materials that contain mineral fibre, expanded vermiculite and/or other lightweight aggregates or fillers. This type of protection is applied in situ and it is particularly suitable for members that have complex profiles and are not visible in use. However, spraying the protection in situ may require extensive shielding and affect the construction programme. Intumescent coatings In contrast with the non-reactive boards and sprays, intumescent coatings react in fire, and change their properties from an initial decorative paint into an intumescent layer of carbonaceous char, by swelling to about 50 times their original thickness. Typical initial thicknesses of 0,25 to 2,5 mm can provide a fire resistance of 30 to 120 minutes, as shown in Figure 3.5. Intumescent coatings are similar in appearance to conventional paints, and may be solvent based or water borne. They consist of three layers which include a compatible primer, the intumescent coat and a top coat or sealer coat (often available in a wide range of colours). Currently, most intumescent coatings are applied off site to aid the construction programme. 0.0 1.0 2.0 3.0 4.0 5.0 30 60 90 Fire resistance(mins) Thickness (mm) Figure 3.5 Intumescent coatings Some intumescent coatings are also used for external applications and for heritage applications, where the appearance of the building must be maintained. 3.2.2 Thickness of fire protection materials For a given product, the thickness of fire protection depends on the required fire resistance and on the section factor of the steel members. The section factor varies with the choice of fire protection and with the type and size of steel member. Figure 3.6 gives expressions to calculate the section factor, based on the configuration of fire protection and on the geometric properties of the steel section.