The explosive limits define a flammable range between which two concentrations?

• A. LEL and UEL
• B. Flashpoint and LEL
• C. Autoignition and flashpoint
• D. Ignition temperature and flashpoint

Answer: (A)

Explosive limits describe the flammable range of a vapor in air as the span between the lower explosive limit and the upper explosive limit. The lower explosive limit is the minimum concentration of fuel in air that can sustain combustion, while the upper explosive limit is the maximum concentration above which the mixture is too rich to ignite. When the vapor concentration in air falls between these two limits, an ignition source can cause combustion or an explosion. Outside this range, the mixture is either too lean to burn or too rich to sustain ignition. So the two concentrations defining the flammable range are the lower explosive limit and the upper explosive limit.