Which is a two-dimensional fire?

A two-dimensional fire is characterized by its ability to spread over a flat surface without significant vertical extension. An ignited flammable liquid spill on open ground exemplifies this as it primarily spreads along the ground, maintaining a flat plane, and its intensity and behavior are dictated largely by the characteristics of the liquid and the surface it’s on.

In contrast, a ground cover fire can also spread across a surface but tends to involve vegetation, which may have varying heights and densities, resulting in a more complex behavior that can include vertical flames. A roof fire typically involves a structure and the flames can spread upward, exhibiting a vertical component and leading to a three-dimensional character. Lastly, a fire contained within a void space is inherently three-dimensional as its characteristics and growth patterns are influenced by the limitations of the enclosed area, including the ceiling height and structural elements. Therefore, the ignited flammable liquid spill is the clearest representation of a two-dimensional fire.