What is the lower limit of flammability in air as a percent of vapor in air/gas mixture?

The lower limit of flammability, also known as the lower explosive limit (LEL), refers to the lowest concentration of a gas or vapor in air that can propagate a flame. In the context of LP (liquefied petroleum) gas, which is primarily composed of propane and butane, the LEL is typically around 2.15% by volume in air. This means that when the concentration of the gas vapor in air is below this level, it is too lean to ignite.

Understanding the LEL is critical for safety in handling flammable gases, as working with or around concentrations at or above this limit increases the risk of fire or explosion. This value is determined through specific testing under controlled conditions to determine the minimum proportion of gas necessary for combustion.

While other options may represent concentrations that are above the LEL or entirely incorrect for typical flammable gas mixtures, the value of 2.15% is the recognized standard for LP gas in standard atmospheric conditions. This standard informs safety regulations and practices in the industry, highlighting the importance of monitoring flammable gas levels in various applications.