The term LEL, in short, is the initial letter of the Lower Explosion Level in English and means the lower explosion limit. The concentration limits of the various gases present in the working environment which do not present a risk of flammability or explosion are called LEL, lower explosion limit. Naturally, each LEL value is different depending on the chemical properties of the gases.

If the gas is to be detected in the measurements, the devices to be measured must be calibrated according to this gas.

LEL values ​​of some gases are as follows: acetone percent 2.5, acetylene percent 2.5, benzene percent 1.2, butane percent 1.9, butyl alcohol percent 1.4, diethyl ether percent 1.9, ethane percent 3, ethyl alcohol percent 3.3, ethylene percent 2.7, hexane percent 1.1, hydrogen percent 4, methane percent 5, methyl alcohol percent 6.0 and toluene percent 1.1.

In our country and in foreign countries, petroleum, petroleum products, natural gas, coal mines, chemical and similar sectors, working environments in various situations such as leaking gases or petroleum vapor are exposed to an explosion risk. It is a legal obligation that employers have taken the necessary measures in order to prevent these situations. Otherwise, there are explosions in many sectors and the desired injuries and deaths are encountered and material damages occur.

Preventing the formation of explosive environments, and if this is not possible to minimize the impact of the explosion, is effective in preventing such accidents.

The Ministry of Labor and Social Security issued the Occupational Health and Safety Law in 2012 in order to regulate the duties, powers and responsibilities of employers and employees in order to ensure occupational health and safety in work environments and to improve existing health and safety conditions. Under this law, employers must ensure the health and safety of employees. In principle, businesses have to avoid risks, analyze risks if it is not possible to avoid, and combat these risks at source.

For this purpose, enterprises have to carry out necessary measurement, test and analysis studies. In this context, LEL gas measurements are made according to the chemical properties of various gases in the environment according to their field of activity. These measurements are carried out by authorized test and inspection institutions. During the measurements, legal regulations in force and standards published by local and foreign organizations are taken into consideration.

Briefly, enterprises must ensure that the working environment is not dangerous for safety and that, in addition to the application of the specified rules, the control of the explosive limits and the mixture of air and gas and the source of explosion, which causes combustion and explosion, are controlled. Essentially for an explosion to occur, there must be oxygen, a combustible substance and an ignition source. LEL is the lowest amount that will cause a volumetric explosion when present in ambient air. In contrast, the UEL is the highest limit value at which it can maintain a volumetric burst when present in ambient air.