“LEL” is an acronym which stands for “Lower Explosive Limit.” The lower explosive limit is the absolute lowest concentration, in percentage, of a gas or a vapor in an environment that would be able to ignite and procure a flash fire in the presence of heat, flame, or an arc.
Gas-detection systems present the wearer with a reading that is a percentage of the Lower Explosive Limit. What this means is that if your gas detector takes a reading that is 100%, you are at the lower explosive limit of the particular gas you are measuring for and should take immediate effort to clear the area, either of yourself or the gas. If your gas detector reads 5%, then you are 5% of the way to the Lel.
If the concentration of gas in a given area is below the Lower Explosive Limit, this means that the gas is too lean to ignite. There’s not enough volume present to ignite the mixture, and it is not flammable. There are also concentrations that are deemed too rich to ignite. To find the lower and upper explosive limits of any gas, look up charts online to find the measurements that you should be concerned about. There are excellent resources out there that keep you informed and safe.
Below is a table with the Lower and Upper Explosive Limits for a multitude of gases. I’ll include a link to the page below as well so that you can print the entire sheet out for your own records.
Below is a video that will demonstrate the Lower Explosive Limit for gasoline vapors.
If you need to calculate the Lower Explosive Limit for a particular gas, please visit this link and use their online calculator that will do the calculation for you automatically.
Above all else, stay safe! Thank you for reading.