Little Pro on 2016-01-13
Explosive limits specify the concentration range of a material in air which will burn or explode in the presence of an ignition source. There are two types of explosive limits: lower explosive limit (LEL) and upper explosive limit (UEL). The explosive limits are usually given as the percent by volume of the material in the air (i.e., 5%). You can often find it in the section 9 of a safety data sheet (SDS).
Lower explosive limit (LEL): the lowest concentration of gas or vapour which will burn or explode if ignited.
Upper explosive limit (UEL): the highest concentration of gas or vapour which will burn or explode if ignited.
From the LEL to the UEL, the mixture is explosive. Below the LEL, the mixture is too lean to burn. Above the UEL, the mixture is too rich to burn. However, concentrations above the UEL are still very dangerous because, if the concentration is lowered (for example, by introducing fresh air), it will enter the explosive range. [Reference]
Exposure limits are only required for materials that may end up in air to cause an explosion. Such materials may include gas, vapor and dusts (i.e, metal powder). Engineering control measures need to be taken to reduce the concentration of such materials in air to avoid potential explosion.
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