What should you use to extinguish an on-board fire if you don't have an extinguisher?

Using sand to extinguish an on-board fire is an effective method due to its ability to smother flames. When sand is poured over a fire, it helps to cut off the fire's access to oxygen, which is essential for combustion. In a vehicle fire scenario, you typically want to use materials that can safely suffocate the flames without causing additional hazards.

Water can sometimes exacerbate certain types of fires, especially if the fire involves flammable liquids or electrical components, as it might spread the flames or conduct electricity. Baking soda is occasionally used for small grease fires, but it might not be practical for an extensive vehicle fire. Flour is not recommended as it can be highly flammable and may even lead to an explosive situation if aerosolized.

Thus, using sand is the safest and most effective alternative when an extinguisher is not available, as it will effectively smother the fire and reduce the risk of it spreading.