Which item is NOT considered flammable?

Concrete is not considered flammable because it is a non-combustible building material that does not ignite or burn. Instead, it is used for structural applications due to its ability to withstand high temperatures and its inherent properties that make it resistant to fire. In contrast, gasoline, grease, and oils can easily catch fire and support combustion, making them hazardous in environments where flammable substances are present. Understanding the differences between flammable and non-flammable materials is crucial for safety in fire-related situations.