What do LEL%/VOL% and ppm mean when used to detect gas?
With the development of technology, gas detectors have become widely used in industries such as petrochemicals, chemical manufacturing, pharmaceutical microbiology, etc. Whether it is detecting gas concentration, gas composition, or detecting gas micro leaks, a useful gas detector can provide a safe environment for our production and life. When we use gas detectors in our daily lives, the detection range on the liquid crystal label of the gas detector often appears with words such as 0-100LEL% or 0-2000ppm, or the words VOL% or ppm may also appear on the liquid crystal display screen of the gas detector. So, what are the specific meanings of these three units and how are they converted? Today, we will give you a detailed introduction.
1, VOL% (gas volume percentage)
VOL is a physical unit that describes the volume of a gas and is expressed as a percentage. It is the percentage of the volume of a specific gas in the air. 5% VOL methane represents 5% of the volume of methane in the air. Our gas detector's detection range is often expressed as VOL%, for example, the detection range is 0-100% VOL, which means that when detecting a certain gas, this gas detector can detect its proportion in the air in the range of 0-100%. We can also set a certain percentage value of VOL as the alarm point. When the content of a certain gas reaches or exceeds this set value, the gas detector will sound an alarm. This involves another unit, LEL%.
2, LEL% (lower explosive limit)
We have previously introduced combustible gases. The concept of combustible gases refers to the ability to mix uniformly with air (or oxygen) within a certain concentration range to form a premixed gas. When encountering a fire source, it will explode. Therefore, the minimum volume percentage concentration at which this combustible gas can detonate in air, which is what we call the lower explosive limit concentration of gas, LEL%, abbreviated as the lower explosive limit. His unit is also a percentage, which divides the lower explosive limit into 100 parts, with each unit being 1LEL%. The concentration of gas volume inside the lower explosive limit is expressed in VOL%.
3, PPM (parts per million of gas volume percentage)
The concept of PPM is similar to VOL, but PPM represents one millionth of a gas volume. For example, 10ppm carbon dioxide refers to carbon dioxide in the air that contains 10 parts per million. Since PPM units are dimensionless, most gas detectors that can detect PPM level leaks are used to detect gas micro leaks in the working environment. Because gas micro leaks are very dangerous, long-term gas micro leaks may cause major accidents, so we need to use PPM level gas detectors to promptly eliminate the location of micro leaks.
4, Conversion of VOL%, LEL%, and PPM
Firstly, there is the conversion between VOL and PPM. The conversion between these two units is relatively simple, as% VOL is the percentage of volume, while PPM is the parts per million of volume. Therefore, 1% (VOL)=10000PPM.
To convert VOL and LEL, we need to first find out the lower explosive limit of the combustible gas. When the concentration of combustible gas in the air reaches its lower explosive limit, we call the explosion hazard level of the combustible gas environment in this place 100%. For example, the LEL of hydrogen is 4% VOL, which means that when its volume percentage in the air reaches 4% VOL, it will explode when exposed to an open flame. Therefore, considering 4% VOL as 100% hazard, it is called 100% LEL, which means 4% VOL=100% LEL, and 1% VOL=25% LEL.
