Answer: The petrol fires are also known as class B fires. Class B fires can be extinguished by foam, powder or carbon dioxide extinguishers.Fire extinguishers with a Class B rating are effective against flammable liquid fires. These can be fires where cooking liquids, oil, gasoline, kerosene, or paint have become ignited. Two commonly used chemicals are effective in fighting these types of fires.
Step-by-step explanation:
When we are applying water on a petrol fire, we cannot stop the supply of the basic three elements which are oxygen, fuel and heat. Since water is heavier than petrol, petrol will come above the water and continue the contact with the atmosphere (oxygen). Already the existing temperature of the atmosphere will be high due to the fire, most of the water poured will evaporate faster. So, we cannot stop the petrol fires using water.