Solution:

At airports and petrol pumps, a foam-type fire extinguisher is used.

The foam type of fire extinguisher is also called a soda acid fire extinguisher. It consists of sulphuric acid and sodium bicarbonate (soda). When it is released under high pressure in the form of foam, it covers the surface of fire and controls it by cutting off oxygen. Water cannot be used as it is heavier than petrol, oil, and kerosene. Sand and blankets are used for small fires. So foam-type of fire extinguisher is idle for fire at airports and petrol pumps.