Which type of foam proportioning system is used in ARFF apparatus?

The correct answer, direct-injection foam proportioning system, is widely utilized in ARFF (Aircraft Rescue and Firefighting) apparatus due to its efficiency and effectiveness in delivering concentrated foam directly into the fire stream. This system allows for an immediate mixing of the foam with the water, ensuring that the foam is optimally concentrated at the point of application.

Direct-injection systems are advantageous in aviation firefighting because they provide a reliable method to produce a consistent foam solution, allowing firefighters to respond quickly and effectively to various fire situations involving aircraft. This direct integration enhances the performance of the foam, improving extinguishment capabilities against flammable liquids typically associated with aviation incidents.

In contrast, the other systems mentioned, such as balance pressure, spray-dispersal, and mixing chamber systems, while they may have their specific applications, do not offer the same level of immediate integration and concentration control that direct-injection systems provide. These alternate systems might involve more complex processes or slower response times, which can be a significant drawback in the fast-paced environment of aircraft firefighting.