Final answer:
The Lower Explosive Limit (LEL) is the least concentration of vapor or gas in the air that is flammable.
Step-by-step explanation:
The term you are looking for is the Lower Explosive Limit (LEL). The LEL is the least concentration of vapor or gas in the air that is flammable. It is the minimum amount of a substance required to produce a fire or explosion when mixed with air or oxygen.
For example, if the LEL of a particular gas is 4%, it means that any concentration of that gas in the air below 4% will not support combustion and is considered too lean to ignite. However, once the concentration reaches or exceeds 4%, it becomes flammable and poses a fire hazard.