Final answer:
The lower flammability level of a gas or vapor of a flammable liquid is the concentration at which it can ignite and sustain a flame. It is important to handle and store flammable liquids safely to prevent fires and explosions.
Step-by-step explanation:
The lower flammability level of a gas or vapor of a flammable liquid is the concentration at which the gas or vapor can ignite and sustain a flame when exposed to an ignition source. This level is also known as the Lower Flammable Limit (LFL) or Lower Explosive Limit (LEL).
For example, gasoline has an LFL of approximately 1.4% volume concentration in air. This means that gasoline vapors in the air must be at least 1.4% concentration before it can ignite and sustain a flame.
It is important to note that different flammable liquids have different LFLs and it is essential to handle and store them safely to prevent fires and explosions.