concrete, resulting in collapse. In a severe fire, 'spalling' (or breaking off) of the surface material occurs and is aggravated if the hot concrete is suddenly chilled, for example with a jet of water. Note: Concrete made with limestone or lightweight aggregates is very much less susceptible to spalling than those made with more dense aggregates, hence the fire resistance of structural concrete is classified differently. Fire and Smoke Penetration and transfer of excessive heat The requirement for resistance to fire penetration is often referred to as ' Integrity ' , which means, in simple words, the element of a structure's ability to prevent a local failure such that under fire conditions, fire and if required smoke, will not penetrate through the structure. After a fire breaks out in a building, hot smoke is generated in the immediate vicinity, and cold smoke can spread quickly through the building, which can affect other people and properties some distance away from the fire. Fire and smoke protection products can be used to prevent or restrict some of these conditions occurring, such as putting in place, dampers, air transfer grilles or other fire-resistant materials. Fire-resistant materials can be added to the structural elements to improve their integrity. Maintenance and repairs should be carried out where possible, such as doing the correct repairs of any holes found in walls or doors. The requirement for resistance to the transfer of excessive heat is often referred to as 'Insulation' . This means, in simple words, the ability to prevent heat transfer through a structure under fire conditions such that the heat will not ignite items on the remote side of the structure. It should now be identified that the insulation of steelwork is paramount to the level of resistance to the collapse of the building or structure. Although metals commonly used in the construction of a building are not combustible and present no risk of fire spread from direct burning, unprotected metal surfaces can constitute a serious risk in a fire because all metals heat up and expand when exposed to fire and are a potential cause of fire spread by conduction. A method used frequently in construction to prevent the transfer of excessive heat is the encasement or 'boxing' in of steelwork and wooden beams, typically more so on steelwork. In this application, the material used to encase the steelwork is of a high fire rating and is used to insulate the metal from the heat source therefore greatly reducing the potential for the steel to become heated, this in turn reducing the potential for the metal to conduct heat elsewhere. Also, by reducing the amount of available heat to the steel construction, the potential for the structure to warp and fail is also greatly reduced. In the illustration that follows, we can see how the encasement of both a cross-member and an upright steel girder has been achieved. The encasing 'boards' are depicted in pink, the materials used to make the boarding are of low heat conductivity, thus protecting the steel beams and columns from the heat source.
©SHEilds – All rights reserved FC V 5 JUN 2021
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