“LEL†refers to the lower explosion limit. The lowest concentration of flammable gas in the air in the event of an explosion of explosives is called the lower explosion limit - referred to as %LEL. The highest concentration of flammable gas in the air in the event of an explosion of explosives is called the upper limit of the explosion - referred to as %UEL. So what is the lower explosion limit? The concentration of flammable gas is too low or too high. It is not dangerous. It only mixes with air to form a mixture or, more specifically, a certain proportion of the mixture of oxygen will burn or explode. . Relevant authorities and experts have made combustion and explosion analysis of the currently found flammable gas, and formulated the explosive limit of flammable gas. Below the lower explosion limit, the content of flammable gas in the mixed gas is insufficient to cause combustion or explosion. The amount of oxygen in the upper limit mixture is insufficient to cause combustion or explosion. In addition, the combustion and explosion of flammable gases are also related to factors such as gas pressure, temperature, and ignition energy. The explosion limit is generally expressed in terms of volume percent concentration.
The explosion limit is the general term for the lower explosion limit and the upper explosion limit. The concentration of flammable gas in the air will only explode between the lower explosion limit and the upper explosion limit. No explosion will occur below the lower explosion limit or above the upper explosion limit. Therefore, when performing an explosion measurement, the alarm concentration is generally set below 25% LEL of the lower explosion limit. The measurement range of various combustible gas detectors is 0-100% LEL.
The fixed flammable gas detector usually has two alarm points: 10% LEL is the first level alarm, and 25% LEL is the second level alarm.
Portable flammable gas detectors usually have an alarm point: 25% LEL is the alarm point. For example, the lower explosion limit of methane is 5% by volume, that is to say, the 5% volume ratio is one hundred aliquots, so that the 5% volume ratio corresponds to 100% LEL, that is, when the detector value reaches 10 When the %LEL alarm point is equivalent to the methane content of 0.5% by volume. When the detector value reaches the 25% LEL alarm point, the methane content is equivalent to 1.25% by volume. Therefore, you don't have to worry about whether it is dangerous at any time after the alarm. At this time, you are prompted to take appropriate measures, such as opening the exhaust fan or cutting off some valves, etc., from the real explosion limit that may be dangerous. There is still a big gap, so that it will play the role of alarm.
"PPM" is the volumetric concentration: "PPM" is a means of expressing the concentration of the solution, and PPM is one in a million. For solution: 1/1000 ml of solute in a 1 liter aqueous solution, the concentration is 1 PPM. For gas: one of the means of expressing the concentration of pollutants in the ambient atmosphere. Volume concentration representation: The volume of contaminants contained in one million volumes of air, ie PPM, the gas concentration measured by most gas detection instruments is the volume concentration (PPM), and according to China's regulations, especially the environmental protection department , the gas concentration is required to be expressed in units of mass concentration, and the standard specifications of our country are also expressed in units of mass concentration. It is made by using some metal oxide semiconductor materials to change the conductivity with changes in the composition of the ambient gas at a certain temperature.
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