What is the primary function of a foam proportioner?

The primary function of a foam proportioner is to introduce foam concentrate into the water stream. This process is critical because it enables the mixing of water with foam concentrate in the right proportion, creating a foam solution that can effectively suppress fire. The proportioner's design ensures that the foam is dispensed at the correct ratio, which is essential for the foam to function properly and provide the desired extinguishing capabilities.

When foam is applied to a fire, it forms a blanket over the burning material, which not only smothers the flames but also prevents re-ignition by cutting off the fire’s access to oxygen. Thus, the proper introduction of foam concentrate into the water stream is vital for achieving effective fire suppression in various scenarios, particularly involving flammable liquids. This is the reason why the choice associated with introducing foam concentrate is the correct one compared to other options that focus on solid barriers, water pressure, or cooling with a water spray, which do not encapsulate the specific role of a foam proportioner.