Nitrogen The inclination to ignition is characterized by an empirical parameter, the ignition temperature i. Depending upon whether or not this parameter is determined-with special test methods-by the use of any ignition source, we distinguish between the piloted ignition temperature and the auto ignition temperature.
In the case of piloted ignition, the energy required for the activation of the materials involved in the burning reaction is supplied by ignition sources.
We will write a custom essay sample on Fire Hazards or any similar topic specifically for you Do Not Waste HIRE WRITER However, there is no direct relationship between the heat quantity needed for ignition and the ignition temperature, because although the chemical composition of the components in the combustible system is an essential parameter of ignition temperature, it is considerably influenced by the sizes and shapes of materials, the pressure of the environment, conditions of air flow, parameters of ignition source, the geometrical features of the testing device, etc.
This is the reason for which the data published in literature for autoignition temperature and piloted ignition temperature can be significantly different. The ignition mechanism of materials in different states may be simply illustrated. This involves examining Essay on fire hazards as either solids, liquids or gases.
Most solid materials take up energy from any outer ignition source either by conduction, convection or radiation mostly by their combinationor are heated up as a result of the heat-producing processes taking place internally that start decomposition on their surfaces.
For ignition to occur with liquids, these must Essay on fire hazards the formation of a vapour space above their surface that is capable of burning.
The vapours released and the gaseous decomposition products mix with the air above the surface of liquid or solid material. The particles induced enter into interaction, resulting in the release of heat.
The process steadily accelerates, and as the chain reaction starts, the material comes to ignition and burns. The combustion in the layer under the surface of solid combustible materials is called smouldering, and the burning reaction taking place on the interface of solid materials and gas is called glowing.
Burning with flames or flaming is the process in the course of which the exothermic reaction of burning runs in the gas phase. This is typical for the combustion of both liquid and solid materials. Combustible gases burn naturally in the gas phase.
It is an important empirical statement that the mixtures of gases and air are capable of gnition in a certain range of concentration only.
This is valid also for the vapours of liquids. The lower and upper flammable limits of gases and vapours depend on the temperature and pressure of the mixture, the ignition source and the concentration of the inert gases in the mixture.
Ignition Sources The phenomena supplying heat energy may be grouped into four fundamental categories as to their origin Sax The following discussion addresses the most frequently encountered sources of ignition. Open flames Open flames may be the simplest and most frequently used ignition source.
A large number of tools in general use and various types of technological equipment operate with open flames, or enable the formation of open flames. Burners, matches, furnaces, heating equipment, flames of welding torches, broken gas and oil pipes, etc.
Because with an open flame the primary ignition source itself represents an existing self-sustaining combustion, the ignition mechanism means in essence the spreading of burning to another system.
Provided that the ignition source with open flame possesses sufficient energy for initiating ignition, burning will start.
The materials inclined to spontaneous heating and spontaneous ignition may, however, become secondary ignition sources and give rise to ignition of the combustible materials in the surroundings.
Although some gases e. Spontaneous ignition, like all ignitions, depends on the chemical structure of the material, but its occurrence is determined by the grade of dispersity. The large specific surface enables the local accumulation of reaction heat and contributes to the increase of temperature of material above spontaneous ignition temperature.
Spontaneous ignition of liquids is also promoted if they come into contact with air on solid materials of large specific surface area.
Fats and especially unsaturated oils containing double bonds, when absorbed by fibrous materials and their products, and when impregnated into textiles of plant or animal origin, are inclined to spontaneous ignition under normal atmospheric conditions.
Spontaneous ignition of glass-wool and mineral-wool products produced from non-combustible fibres or inorganic materials covering large specific surfaces and contaminated by oil have caused very severe fire accidents.
Spontaneous ignition has been observed mainly with dusts of solid materials. For metals with good heat conductivity, local heat accumulation needed for ignition necessitates very fine crushing of metal.
As the particle size decreases, the likelihood of spontaneous ignition increases, and with some metal dusts for example, iron pyrophorosity ensues. When storing and handling coal dust, soot of fine distribution, dusts of lacquers and synthetic resins, as well as during the technological operations carried out with them, special attention should be given to the preventive measures against fire to reduce the hazard of spontaneous ignition.
Materials inclined to spontaneous decomposition show special ability to ignite spontaneously. Hydrazine, when set on any material with a large surface area, bursts into flames immediately.
The peroxides, which are widely used by the plastics industry, easily decompose spontaneously, and as consequence of decomposition, they become dangerous ignition sources, occasionally initiating explosive burning.
The violent exothermic reaction that occurs when certain chemicals come into contact with each other may be considered a special case of spontaneous ignition. Examples of such cases are contact of concentrated sulphuric acid with all the organic combustible materials, chlorates with sulphur or ammonium salts or acids, the organic halogen compounds with alkali metals, etc.
It is worth mentioning that such hazardously high spontaneous heating may, in some cases, be due to the wrong technological conditions insufficient ventilation, low cooling capacity, discrepancies of maintenance and cleaning, overheating of reaction, etc.
Certain agricultural products, such as fibrous feedstuffs, oily seeds, germinating cereals, final products of the processing industry dried beetroot slices, fertilizers, etc.Fire safety becomes everyone's job at a worksite. Employers should train workers about fire hazards in the workplace and about what to do in a fire emergency.
This plan should outline the assignments of key personnel in the event of a fire and provide an evacuation plan for workers on the site. In. Fire Hazards And Precautions. Print Reference this. Disclaimer: Click on this link for a useful flash tutorial on fire extinguishers.
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