What term describes the nature of the material first ignited in a fire?

The correct term that describes the nature of the material first ignited in a fire is referred to as the "form of material." This term encompasses the specific characteristics and properties of the material, which can influence how it ignites, burns, and contributes to the development and spread of fire. Understanding the form of a material helps firefighters and investigators determine the behavior of the fire, assess risks, and implement effective firefighting strategies.

The other options do not accurately capture the concept of the material first ignited. "Type of fire" refers to the classification of fires based on the materials involved (e.g., Class A for ordinary combustibles, Class B for flammable liquids) rather than the specific material that ignites first. "Source of ignition" pertains to the origin or cause of the ignition, such as a spark, flame, or heat source, rather than describing the material itself. Lastly, "material classification" generally categorizes materials based on their properties or behaviors but does not specifically address the initial material that catches fire.