PPM "is the volume specific concentration. PPM "is a representation of solution concentration, where PPM represents parts per million. For a solution: if there is 1/1000 milliliter of solute in 1 liter of aqueous solution, the concentration is 1 PPM. For gases: One of the methods for expressing the concentration of pollutants in the ambient atmosphere. Volume concentration representation: The volume of pollutants contained in one million volumes of air, known as PPM. Most gas detection instruments measure gas concentrations as volume concentration (PPM). According to Chinese regulations, especially environmental protection departments, gas concentrations are required to be expressed in units of mass concentration. Our national standards and regulations also use mass concentration units to represent gas concentrations. It is manufactured using the principle that the conductivity of some metal oxide semiconductor materials changes with the composition of the environmental gas at a certain temperature.
LEL "refers to the lower explosive limit. The minimum concentration of combustible gases that can explode when exposed to an open flame in the air is called the lower explosive limit - referred to as percent LEL.
The maximum concentration of combustible gases that can explode when exposed to an open flame in the air is called the upper explosion limit - referred to as percent UEL. So what is the lower explosive limit? The concentration of combustible gases is too low or too high, and it is not dangerous. It only burns or explodes when it mixes with air to form a mixture or, more precisely, when it encounters oxygen to form a certain proportion of the mixture. Relevant authoritative departments and experts have conducted combustion and explosion analysis on the currently discovered combustible gas, and established an explosion limit for combustible gas below the lower explosion limit. The content of combustible gas in the mixture is insufficient to cause combustion or explosion, and the oxygen content in the mixture above the upper limit is insufficient to cause combustion or explosion.
Therefore, when conducting explosion measurements, the alarm concentration is generally set below 25 percent LEL of the lower explosion limit. The measurement range of various combustible gas detectors is 0-100 percent LEL. Fixed combustible gas detectors usually have two alarm points: 10 percent LEL is the first level alarm, and 25 percent LEL is the second level alarm. Portable combustible gas detectors usually have an alarm point: 25 percent LEL is the alarm point.
For example, the lower explosive limit of methane is 5 percent by volume ratio. That is to say, divide this 5 percent by volume ratio into 100 equal parts, so that the 5 percent by volume ratio corresponds to 100 percent LEL. That is to say, when the detector value reaches the 10 percent LEL alarm point, it is equivalent to the methane content being 0.5 percent by volume ratio at this time. When the detector value reaches the 25 percent LEL alarm point, it is equivalent to a methane content of 1.25 percent by volume at this time.
