What characteristics define a flammable liquid?

The defining characteristic of a flammable liquid is its flash point, which is the lowest temperature at which it can vaporize to form an ignitable mixture in air. The correct choice highlights that a flammable liquid has a flash point below 100 degrees Fahrenheit, which classifies it as capable of creating flammable vapors at relatively low temperatures. The presence of specific vapor pressure in this context further supports the likelihood of ignition, as higher vapor pressures indicate a greater concentration of vapors that can mix with air and ignite.

A flash point below 150 degrees Fahrenheit captures a broader range of ignitable substances; however, it does not give the precise threshold for defining flammability, which is crucial in safety and handling protocols. Simply stating that a liquid is any liquid capable of igniting in air is too vague and lacks the needed specificity regarding temperature conditions. Finally, the aspect of special storage requirements does not necessarily define a liquid as flammable but rather relates to safety practices for certain hazardous materials, which might include flammable liquids but are not definitive. Therefore, the option focusing on the specific flash point and vapor pressure offers the most accurate and relevant definition of a flammable liquid.