Why is water strictly prohibited as an extinguishing agent on Class B hydrocarbon liquid fires and Class C electrical fires

Water is strictly prohibited for Class B hydrocarbon liquid fires and Class C electrical fires due to different hazards:

For Class B hydrocarbon liquid fires:
Water is denser than most hydrocarbons, so it will sink below the burning liquid, causing the fire to spread rather than extinguish. It can also lead to a dangerous boil-over or froth-over effect, where rapidly vaporizing water under the hot oil violently ejects burning liquid, spreading the fire further.

For Class C electrical fires:
Water is an electrical conductor. Using water on live electrical equipment poses a severe risk of electric shock to the user and can cause further damage to the electrical system.