Which action is critical when addressing a fire involving a vehicle's hybrid battery?

Using abundant water to cool down the fire involving a vehicle's hybrid battery is critical for multiple reasons. Hybrid batteries, which are often lithium-ion, can generate significant heat during a fire due to chemical reactions, and controlling that heat is paramount to preventing further combustion or explosion.

By applying a large volume of water, you effectively cool the surrounding metal and battery, which helps to extinguish the flames and suppress any reignition of the fire. Additionally, thorough cooling can help manage the risks associated with thermal runaway—a condition where the battery continues to heat up even after extinguishing the external flames due to its internal reactions.

It's important to note that managing water usage is also a consideration in firefighting, particularly for electrical fires, but in the context of a hybrid battery fire, using an adequate amount of water is integral to ensuring safety and mitigating additional hazards.