Grand Theft Auto: San Andreas/Missions/Firefighter

Prerequisites

Vehicle: Fire Truck. You can attract them by setting fires (for example, by shooting cars in their gas tanks or by throwing grenades at them), or go to a fire station to find one parked. One such station is located just south of the Doherty garage in San Fierro.

Aim the water hose above the heads of the victims, not at them (no water canon style hitting). The fire should be put out almost within one second upon you sprinkle the water over them.
Get close to the flaming vehicle. It allows for faster extinguishing of the fire. Note that the flames you fight will not catch the fire truck on fire. Every level adds one person to be saved, and when you have more than three people you will have more than one vehicle. Levels 1-4 have people in the same vehicle, 5-8 will be divided into two vehicles, 9-12 into three, and so on.

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