What is the flammable range of a substance?

The flammable range of a substance refers specifically to the concentration of that substance in the air that can support combustion. This range is defined by two critical points: the Lower Explosive Limit (LEL) and the Upper Explosive Limit (UEL).

At concentrations below the LEL, there is not enough fuel in the air to sustain a fire, while concentrations above the UEL have too much fuel, resulting in insufficient oxygen for combustion. Therefore, the flammable range is the interval between these two limits, where the mixture of air and fuel will ignite if an ignition source is present. This concept is crucial for safety in handling and storing flammable materials, as understanding this range helps prevent potential fire hazards in various environments.