Which property defines a liquid's flammability and helps predict ignition risk?

• A. Boiling Point
• B. Melting Point
• C. Flashpoint
• D. Vapor Pressure

Answer: (C)

Understanding how flammable a liquid is relies on the flashpoint—the lowest temperature at which enough vapor can form an ignitable mixture with air. This temperature shows when ignition is actually possible if a source is present. A low flashpoint means the liquid can ignite at relatively low temperatures, signaling higher ignition risk and a greater fire hazard; a high flashpoint means ignition requires more heat and the material is safer to handle at room temperature or normal conditions.

Boiling point simply tells you when a liquid becomes gas, not when it can ignite at ambient conditions. Melting point describes when a solid becomes a liquid, which isn’t about ignition risk. Vapor pressure indicates how readily a liquid forms vapor, but without tying that vapor to an ignition event at a specific temperature; flashpoint directly ties vapor generation to the possibility of ignition, making it the best measure for flammability and ignition risk.