What geometric depiction represents how fire is sustained by a chain reaction?

The correct depiction of how fire is sustained by a chain reaction is represented by the fire tetrahedron. The fire tetrahedron expands upon the traditional fire triangle by adding a fourth element: the chain reaction. This addition highlights the critical factor in sustaining combustion, which is the self-perpetuating reaction of the free radicals generated during combustion.

In the fire tetrahedron, the four components necessary for fire are heat, fuel, oxygen, and the chemical chain reaction. This understanding is essential in fire protection and prevention strategies, as interrupting any one of these components can help extinguish a fire. The fire triangle, while informative, only includes heat, fuel, and oxygen, and does not account for the chain reaction aspect that is vital to understanding how fires sustain themselves.

Options such as the fire diamond and the fire pentagon do not depict the sustenance of fire through a chain reaction but are instead related to other aspects of fire safety and hazard identification, thus they do not serve as accurate representations in this context.