In order to reduce heat transmission in hollow spaces or cavities (such as those between double partitions, walls, an internal lining, or a roof) they are frequently filled with materials, which are of a loose fibrous nature and have a low conductivity. These are typically non-combustible products such as rock or glass wool, foamed slag, or vermiculite. Intumescent Coatings (penetration seals) Intumescent coatings are made from a combination of products. They are applied to the surface like paint and provide a similar finish. They remain stable at ambient temperatures but are designed to produce a chemical reaction in a fire situation. In this type of condition, the coating expands to many times its original thickness to produce a bulky non-flammable layer of bubbles, which offers good insulation protection to the coated material. In the protection of steelwork, the intumescent coating is designed to insulate the steel and prevent the temperature of the steel from rising above a certain point. The steel and other materials are then protected from the high temperatures of fires thus preventing or retarding structural damage during fires. Intumescent coatings can be used on wood but work in a different manner, timber structures are more susceptible to the surface spread of flame and heat propagation. Intumescents are designed to reduce heat propagation and reduce the spread of flame. As well as being used to protect flammable materials and structural elements, intumescent systems are now being incorporated into certain plastics, thus providing an inherent or passive fire protection capacity. Intumescent technology is not only restricted to material coatings, other products use intumescent technology to provide fire retardation and to inhibit the spread of fire. A widely used product is the intumescent 'pillow' . The illustration that follows shows several of these pillows being layered in combination to fill an electrical cabling route through a block-built wall.
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