What distinguishes nonflammable materials?

Nonflammable materials are distinguished primarily by their inability to ignite and sustain combustion when exposed to flame or high temperatures. When a material is classified as nonflammable, it means that it does not easily catch fire and is not prone to burning, which makes it a safer choice in environments where fire hazards may be present.

The characteristic of nonflammable materials is crucial for various applications in building construction, manufacturing, and fire safety equipment, as these materials can help mitigate risks and prevent fire-related incidents. For instance, metals or certain treated plastics can fall into this category because they do not support combustion, thereby providing a barrier against fire spread.

In contrast, the other choices suggest characteristics that do not align with what makes a material nonflammable. For example, materials capable of burning easily or sustaining combustion would not meet the definition of nonflammable, and materials that spark when heated could pose ignition risks. These attributes clarify why the distinction of being not prone to ignite when exposed to flame is the defining trait of nonflammable materials.