What temperature defines a flammable substance?

A flammable substance is defined as one that can ignite and sustain combustion at relatively low temperatures. In the context of this question, a substance is considered flammable if it has a flash point below 140 degrees Fahrenheit (approximately 60 degrees Celsius). The flash point is the lowest temperature at which the vapor of a substance can ignite in air, hence making it capable of causing a fire.

Substances that are classified based on a flash point below this threshold are commonly recognized as flammable materials because they pose significant risks in terms of fire hazards in various environments. This is crucial knowledge for personnel involved in handling or storing chemicals, as it informs safety protocols and risk assessments. The other temperature options do not align with the established definition of flammable substances, as higher temperatures (like those mentioned in other options) would typically indicate non-flammable or less flammable characteristics.