In vehicle fires, which of the following is NOT a fuel category?

In the context of fire investigation, fuels are typically categorized based on their physical state and characteristics during combustion. The three primary fuel categories are solid, liquid, and gaseous. Each of these categories describes the form that the material takes before it is ignited and how it behaves when it burns.

Electrical materials, while they play a significant role in a variety of fire scenarios, are not classified as a fuel category in the same way that solids, liquids, and gases are. Electrical energy itself does not fall under a physical fuel state; rather, it can lead to a fire by providing an ignition source for flammable materials. Therefore, it does not fit into the conventional classification of fuels, which is why choosing electrical in this scenario is the correct answer to the question about fuel categories in vehicle fires.