In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Situation**: In the event of a fire, firemen need to use water hoses to extinguish the flames. However, before doing so, they take a precautionary step by shutting off the main electrical supply in the area.

2. **Properties of Water**: The water used in fire hoses is not pure distilled water; it is regular tap water, which contains minerals, ions, and salts. These impurities make tap water a good conductor of electricity.

3. **Risk of Electric Shock**: If the electrical supply is not turned off, there is a risk that the water, being a conductor, could carry electrical current. If the firemen are in contact with this water while the electrical supply is active, they could receive an electric shock.

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