What should be secured after all fire extinguishers have been expended during an engine fire?

Securing the fuel supply after all fire extinguishers have been expended during an engine fire is critical to preventing the fire from reigniting or spreading. Fuel is the primary source that sustains a fire, and by cutting off the supply, it minimizes the risk of re-ignition or worsening the situation.

In the context of an engine fire, it is essential to understand that even if the flames are extinguished, fuel that remains in the system can create a hazardous environment. This can lead to potential flare-ups if there is any residual heat or spark that could ignite the remaining fuel.

Though the other options—water, air, and electrical supplies—can play significant roles in fire management and safety, they do not directly address the central issue at hand following a fire extinguishing effort. Water supply may be used to cool surfaces or prevent re-ignition, and managing air supply can be critical for fires involving certain materials, but focusing on the fuel supply is paramount for safety after a fire is under control.