What does LEL stand for in flammable vapor terms?

• A. Minimum concentration of flammable vapor that can ignite.
• B. Maximum concentration of flammable vapor that can ignite.
• C. The rate at which a vapor ignites.
• D. The temperature at which a vapor ignites.

Answer: (A)

Lower Explosive Limit is the minimum concentration of flammable vapor in air that can ignite if an ignition source is present. It marks the lower end of the flammable range; mixtures leaner than this won’t burn because there isn’t enough fuel in the air. The flammable range extends from the LEL up to the Upper Explosive Limit, beyond which the mixture is too rich to ignite. LEL is usually expressed as a percent by volume in air and helps you assess ignition risk and ventilation needs in a workspace. If vapor concentrations get close to the LEL, ignition becomes possible with a spark or flame. The other options describe different ideas: the maximum concentration that can ignite is the UEL; the rate of ignition isn’t defined by the LEL; and the temperature at which a vapor ignites relates to ignition temperature or autoignition/flash point, not the explosive limit.