“Unveiling the “Limits of Explosion”

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This post was last edited by yinkuilin6868 on 2015-11-23 08:51. 1. Explosion limit: Combustible materials (combustible gases, vapors, and dusts) must be evenly mixed with air (or oxygen) within a certain concentration range to form a premixed gas; only when exposed to an ignition source will an explosion occur. This concentration range is known as the explosion limit, or explosive concentration limit. 　　For example, the explosion limit of a mixture of carbon monoxide and air is 12.5%–74%. The lowest and highest concentrations at which a flammable mixture can explode are referred to as the lower explosion limit and the upper explosion limit, respectively; these are sometimes also called the lower ignition limit and the upper ignition limit. It does not explode nor catch fire when below the explosion threshold ； It will not explode when the temperature is above the explosion limit, but it can burn. This is because the combustible material concentration in the former is insufficient, and the cooling effect of the excess air prevents the flame from spreading ； The latter is due to a lack of air, which prevents the flame from spreading. The greatest explosive power is achieved when the concentration of the combustible material is roughly equivalent to the stoichiometric concentration for the reaction (i.e., the concentration ratio calculated based on the complete combustion reaction equation). Controlling gas concentration is an essential aspect of occupational safety. Add an inert gas or other non-flammable gas to reduce the concentration. Before releasing the gases, explosive gases can be removed using scrubbers or adsorption methods. 2 Influencing factors The explosion limit varies depending on the components of the mixture. In the same mixture system, the explosion limit can change due to factors such as the initial temperature, system pressure, amount of inert medium present, the volume in which the mixture is contained, the material of the container walls, and the magnitude of the ignition energy. 　　The general rule is that as the initial temperature of the mixture increases, the explosion limit range expands, that is, the lower limit decreases while the upper limit increases. As the system temperature rises, the internal energy of the molecules increases, turning what was originally an non-flammable mixture into a flammable and explosive one. As system pressure increases, the range of explosion limits also expands. This is because higher pressure brings the molecules closer together, increasing the likelihood of collisions and thus facilitating the combustion reaction. As pressure decreases, the explosion limit range shrinks ； When the pressure drops to a certain value, its upper and lower limits coincide; the pressure corresponding to this point is known as the critical pressure of the mixture. When the pressure drops below the critical pressure, the system is no longer a explosive system (with some gases exhibiting abnormal behavior). As the amount of inert gas in the mixture increases, the range of explosive limits narrows; once the concentration of inert gas reaches a certain value, the mixture can no longer explode. The smaller the diameter of the container or pipe, the smaller the explosion range. When the diameter of the flame channel becomes small enough, the heat dissipated by the solid cooling surface per unit volume of flame exceeds the heat generated, causing the flame to be interrupted and extinguished. The maximum pipe diameter beyond which the flame cannot propagate is known as the critical diameter of that mixture system. A high ignition energy, a large area of the hot surface, and varying contact times between the ignition source and the mixture can all increase the explosion limit. 　　In addition to the factors mentioned above, the material of the enclosed housing in which the mixed systems are in contact, mechanical impurities, light exposure, surfactants, and other elements can all affect the explosion limit range. 3 Hazards The greater the explosion range of a flammable mixture, the lower its lower explosion limit, and the higher its upper explosion limit, the greater its explosion hazard. This is because the wider the explosion limit, the greater the chances of conditions for an explosion occurring ； The lower the explosion threshold, the more likely it is that even a slight leakage of flammable substances will create conditions for an explosion ； The higher the explosion limit, the more air can penetrate into the container, where it can mix with the flammable substances inside to create conditions for an explosion. It should be noted that when the concentration of a flammable mixture exceeds the upper limit for explosion, no ignition or explosion occurs; however, if it escapes from a container or pipeline and comes into contact with air again, it can burn, and there is still a risk of fire. 4 represents the method: Igniting a gas in air; the gas may explode or it may stop burning very quickly. Which situation it is is determined by the concentration of gas in the air. When the gas concentration is too low, there isn’t enough fuel to sustain the explosion ； When the gas concentration is too high, there isn’t enough oxygen for combustion. A gas can explode only between two concentrations, which are referred to as the lower explosive limit (LEL) and the upper explosive limit (UEL), expressed as percentages. They are the explosion limits of gases (also known as explosion boundaries). The explosion limit of a gas or vapor is expressed as a percentage (%) of the volume occupied by the flammable substance in the mixture; for example, the explosion limit of a hydrogen-air mixture is 4% to 75%. The explosion limit of combustible dust is expressed as the mass ratio of the combustible substance to the total volume in the mixture, in units of g/m^3; for example, the explosion limit of aluminum powder is 40 g/m^3. 1 Explosion limit: Combustible materials (combustible gases, vapors, and dusts) must be evenly mixed with air (or oxygen) within a certain concentration range to form a premixed gas; only when this premixed gas comes into contact with a fire source will an explosion occur. This concentration range is known as the explosion limit, or combustion concentration limit. 　　For example, the explosion limit of a mixture of carbon monoxide and air is 12.5%–74%. The lowest and highest concentrations at which a flammable mixture can explode are referred to as the lower explosion limit and the upper explosion limit, respectively; these are sometimes also called the lower ignition limit and the upper ignition limit. It does not explode nor catch fire when below the explosion threshold ； It will not explode when the temperature is above the explosion limit, but it can burn. This is because the combustible material concentration in the former is insufficient, and the cooling effect of the excess air prevents the flame from spreading ； The latter is due to a lack of air, which prevents the flame from spreading. The greatest explosive power is achieved when the concentration of the combustible material is roughly equivalent to the stoichiometric concentration for the reaction (i.e., the concentration ratio calculated based on the complete combustion reaction equation). Controlling gas concentration is an essential aspect of occupational safety. Add an inert gas or other non-flammable gas to reduce the concentration. Before releasing the gases, explosive gases can be removed using scrubbers or adsorption methods. 2 Influencing factors The explosion limit varies depending on the components of the mixture. In the same mixture system, the explosion limit can change due to factors such as the initial temperature, system pressure, amount of inert medium present, the volume in which the mixture is contained, the material of the container walls, and the magnitude of the ignition energy. 　　The general rule is that as the initial temperature of the mixture increases, the explosion limit range expands, that is, the lower limit decreases while the upper limit increases. As the system temperature rises, the internal energy of the molecules increases, turning what was originally an non-flammable mixture into a flammable and explosive one. As system pressure increases, the range of explosion limits also expands. This is because higher pressure brings the molecules closer together, increasing the likelihood of collisions and thus facilitating the combustion reaction. As pressure decreases, the explosion limit range shrinks ； When the pressure drops to a certain value, its upper and lower limits coincide; the pressure corresponding to this point is known as the critical pressure of the mixture. When the pressure drops below the critical pressure, the system is no longer a explosive system (with some gases exhibiting abnormal behavior). As the amount of inert gas in the mixture increases, the range of explosive limits narrows; once the concentration of inert gas reaches a certain value, the mixture can no longer explode. The smaller the diameter of the container or pipe, the smaller the explosion range. When the diameter of the flame channel becomes small enough, the heat dissipated by the solid cooling surface per unit volume of flame exceeds the heat generated, causing the flame to be interrupted and extinguished. The maximum pipe diameter beyond which the flame cannot propagate is known as the critical diameter of that mixture system. A high ignition energy, a large area of the hot surface, and varying contact times between the ignition source and the mixture can all increase the explosion limit. 　　In addition to the factors mentioned above, the material of the enclosed housing in which the mixed systems are in contact, mechanical impurities, light exposure, surfactants, and other elements can all affect the explosion limit range. 3 Hazards The greater the explosion range of a flammable mixture, the lower its lower explosion limit, and the higher its upper explosion limit, the greater its explosion hazard. This is because the wider the explosion limit, the greater the chances of conditions for an explosion occurring ； The lower the explosion threshold, the more likely it is that even a slight leakage of flammable substances will create conditions for an explosion ； The higher the explosion limit, the more air can penetrate into the container, where it can mix with the flammable substances inside to create conditions for an explosion. It should be noted that when the concentration of a flammable mixture exceeds the upper limit for explosion, no ignition or explosion occurs; however, if it escapes from a container or pipeline and comes into contact with air again, it can burn, and there is still a risk of fire. 4 represents the method: Igniting a gas in air; the gas may explode or it may stop burning very quickly. Which situation it is is determined by the concentration of gas in the air. When the gas concentration is too low, there isn’t enough fuel to sustain the explosion ； When the gas concentration is too high, there isn’t enough oxygen for combustion. A gas can explode only between two concentrations, which are referred to as the lower explosive limit (LEL) and the upper explosive limit (UEL), expressed as percentages. They are the explosion limits of gases (also known as explosion boundaries). The explosion limit of a gas or vapor is expressed as a percentage (%) of the volume occupied by the flammable substance in the mixture; for example, the explosion limit of a hydrogen-air mixture is 4% to 75%. The explosion limit of combustible dust is expressed as the mass ratio of the combustible substance to the total volume in the mixture, in units of g/m^3; for example, the explosion limit of aluminum powder is 40 g/m^3.