For an Index D classification, what is the minimum total water capacity for foam production across all vehicles?

For an Index D classification, the requirement for foam production includes having a specific total water capacity that ensures effective firefighting capabilities. The correct answer of 4,000 gallons of water and AFFF aligns with the guidelines that dictate the minimum resources necessary for airports to achieve adequate fire protection levels, especially for large aircraft.

An Index D classification involves handling the challenges associated with larger aircraft and potentially more intense fire scenarios. The capacity to use 4,000 gallons, combined with AFFF (Aqueous Film-Forming Foam), is crucial for forming a layer that smothers flames and prevents re-ignition. This specific amount of water not only supports the immediate firefighting needs but also allows for a sustained firefighting effort.

In contrast, lower capacities would not provide sufficient resources during an emergency, risking firefighter safety and effectiveness. Thus, the specification of 4,000 gallons represents a standard within regulatory frameworks for airports operating with larger aircraft, ensuring that they can respond appropriately to incidents that may occur.