Which property defines the flammability range of a vapor in air?

• A. Upper/lower flammability or explosive limits
• B. Flash Point
• C. Relative Density
• D. Solubility

Answer: (A)

Flammability range is defined by the lower and upper flammability limits—the minimum and maximum vapor concentrations in air that can support ignition. Below the lower limit the mixture is too lean to burn, and above the upper limit it’s too rich to ignite. The other properties describe different concepts: flash point is about the temperature needed to produce ignitable vapor, while relative density and solubility don’t determine the burning range in air.