Why do firefighters put out a fire on a petrol tanker with foam?

Firefighters use foam to extinguish fires on petrol tankers because foam effectively cools the flames and creates a barrier that prevents oxygen from fueling the fire. The foam also adheres to the surface of the burning fuel, suppressing vapor release and reducing the risk of re-ignition. This method is particularly important for flammable liquids like petrol, where traditional water-based methods can be ineffective or even dangerous. Using foam helps ensure a safer and more efficient firefighting operation.