What is equivalent to 100% LEL in terms of gas concentration?

The term "LEL" stands for Lower Explosive Limit, which is the lowest concentration of gas or vapor in air that can ignite if an ignition source is present. When we refer to 100% LEL, we are indicating a gas concentration at the exact threshold where the gas is capable of supporting combustion.

For various gases, this limit is defined by their specific characteristics. In this case, if 100% LEL corresponds to 5% gas concentration, then 5% is indeed the concentration at which the gas reaches its explosive threshold. Understanding how different gases have their own distinct LEL values is crucial for safety practices.

Considering other concentration levels provided in the choices makes it clear that they do not correspond to the LEL definition for the gas in question. Thus, recognizing that 100% LEL equates to 5% gas allows for prudent evaluation in safety protocols and risk assessments associated with gas handling.