• Acrylic over locks. • Expanded polystyrene. • Flexible polyether (polyurethane foam). • Polypropylene silver. • Rigid polyurethane foam (low density). Other considerations include the type, quantity, distribution, and reactive nature of the materials stored. The conditions required for, mechanisms of, and impacts of flashover and backdraught Open burning fires and fire in a physical enclosure, defined in literal and simplistic examples are something akin to a bonfire and that of a fireplace, i.e. one is contained the other not. Whilst maintaining the basic principles of containment we also need to understand more sophisticated and larger scale examples. In the construction of a building, rooms or areas could be constructed using fire-retaining materials thus creating a physical fire enclosure, which will inhibit the spread or growth of fire. The obvious opposite is open areas or rooms not constructed from suitable materials, which have little if any effect upon the containment of fire growth. Consider fire growth in a domestic house fire and compare a room with a closed door to an open area such as a staircase. Open burning fires and physically enclosed fires In an open burning fire outside a building, such as a bonfire, the hot gases of combustion rise into the atmosphere with very little effect on the temperature of the materials involved in the fire. As a result, the speed of fire growth is generally much slower than it would be in an enclosed space. Most people will be familiar with a fire outdoors, which people can move back from as it grows. If the wind is blowing the smoke towards them, they can move right away from the fire to a place of safety because they have a choice of escape routes not affected by heat or smoke. A fire in a physical enclosure A fire in an enclosed room is however a very different phenomenon to an open burning fire. The speed of fire growth can be devastating, with two fire phenomena of specific note: • Flashover. • Backdraught. Flashover A flashover can occur when a fire is free-burning in a room. For this to happen there must be a good supply of air, either from the large dimensions of the room, an open door, an open window or a ventilation system. As the item that was initially ignited burns and the fire grows, the radiated heat heats up all the other materials in the room until they reach their spontaneous ignition temperature. Items in the room will then instantly ignite, creating the impression that the fire has flashed from one side of the room to the other. Although this phenomenon is very serious, it is not the most dangerous, as it is obvious that there is a severe fire in progress.
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