What is the defining characteristic of combustible materials?

The defining characteristic of combustible materials is that they are capable of undergoing combustion. This means that they have the potential to ignite and sustain a fire when exposed to a sufficient heat source. Combustible materials can be solids, liquids, or gases, and their ability to burn is a fundamental principle in fire investigation, as understanding what materials may ignite can help in determining fire causes and behaviors.

In contrast, materials that cannot burn are classified as non-combustible, and those that require high temperatures to ignite could be considered less flammable or have a higher ignition point but are still considered combustible if they can eventually catch fire under the right conditions. Additionally, the assertion that combustible materials are always solid is not accurate; many liquids and gases are also combustible. Therefore, the capacity to undergo combustion is truly what defines combustible materials.