What is the smallest percentage of vapor in air that can form an ignitable mixture?

The smallest percentage of vapor in air that can form an ignitable mixture is referred to as the lower flammable limit. This term is specifically defined as the minimum concentration of a flammable substance in air, below which the mixture is too lean to ignite. When the concentration of vapor falls below this limit, there are not enough combustible particles present to sustain combustion if an ignition source is introduced.

Understanding the lower flammable limit is crucial for safety in environments where flammable gases or vapors may be present. It helps determine safe handling procedures and necessary precautions when working in areas where vapors can accumulate. Ignoring this limit could lead to hazardous situations where the potential for ignition exists if proper measures are not taken.