electric fires should not be extinguished by water instead of water use sand explain
Answers
Answer:
How does water extinguish fire? Heat energy from the fire is transferred to the water, isn't that how it works? How does water deprive oxygen and stop combustion? How is the specific heat of water connected to this? If we use hot water instead cold water, does that make a difference?
In certain kinds of fire, using water will not work well (or "at all"). That includes fires with liquid fuel - force of water can disperse the fuel into the air and thus the cooling doesn't happen where the fire happens (actually this can make things worse, since many droplets of fuel can now burst into flame away from the base), chemical fires (you might cause additional reactions, or just speed up the reaction by dissolving the components), and fires in which the fuel would react with water - for example certain kinds of metal fires (e.g. magnesium shavings, alkali metals, and the like). You also don't want to add water when there are other risks related to its use (for example high voltages present).
This is why many "general purpose" extinguishers tend to be of the "deprive of oxygen" kind - foam, powder.
Afterthought based on BeastRaban's answer: when water becomes vapor, it is lighter than air, with an atomic mass of 18 vs 29 for the usual oxygen/nitrogen mixture - but being generally cooler than a flame (most vapor will be around 100°C), it may slow down the rate with which fresh air is being drawn into the fire. As such, it is not only a coolant of the fuel (which slows down the rate of the exothermal reaction taking place), but also an asphyxiant, pushing away oxygen (or at least slowing down the rate at which it is being replenished).
Explanation: