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Class “B” fires
It is the vapour of a flammable or combustible liquid, rather the liquid itself, that burns or explodes when mixed with air and ignited. These liquids will vaporize when exposed to air – and at an increased rate when heated. They should be stored in the closed containers of proper type to minimize the fire hazard; even in use they should be exposed to air as little as possible. Flammable vapour explosions most frequently occur within a confined space such as a container, tank, room or a structure. The violence of a flammable vapour explosion depends upon: 1). The concentration and nature of the vapour. 2). The quantity of vapour air mixture presence. 3). The type of enclosure in which the mixture is confined. The flash point is commonly accepted as the most important factor determining the relative hazard of a flammable or combustible liquid. However, it is not the only factor involved. The ignition temperature, flammable range, rate of evaporation, reactivity when exposed to heat, density and rate of diffusion of the vapour also determine how dangerous the liquid is. However, once a flammable or combustible liquid has been burning for a short time, these factors have little effect on its burning characteristics. The burning rates of flammable liquids vary somewhat, as do their rates of flame travel. The burning rate of gasoline is 15 – 30 cm of depth per hour; for kerosene the rate is 13-20 cm of depth per hour. For example, a pool of gasoline of 1,27 cm of depth could be expected to burn itself out in 2,5 to 5 minutes. TEXT 4 Дата добавления: 2015-09-18 | Просмотры: 651 | Нарушение авторских прав |