How is a flammable substance defined?

A flammable substance is defined as any material that can catch fire easily and sustain combustion. This definition emphasizes two critical aspects: the ease with which the material ignites and its ability to continue burning once ignited. Flammable substances typically have low flash points, meaning they can ignite at relatively low temperatures, making them hazardous in many environments, especially where heat sources or sparks are present.

In contrast, the other options describe characteristics that do not align with the definition of flammability. The first option implies that the material is non-combustible, which lacks the fundamental characteristic of flammability. The third option suggests that burning occurs only at high temperatures, which could describe a combustible material but does not apply to flammables, as they can ignite at lower temperatures. The fourth option refers to the release of gases upon heating, which can happen with many substances, but does not inherently indicate that the material is flammable. Therefore, recognizing a flammable substance as one that can easily catch fire and maintain combustion is crucial for understanding and assessing explosion hazards.