Imagine there’s a small fire in your kitchen. Your fire alarm goes off, warning everyone nearby about the danger. Someone calls 911. You try to put the fire out yourself – maybe you even have a fire extinguisher under the sink. If that doesn’t work, you know how to safely evacuate.
By the time you get outside, a fire truck is already pulling up. Firefighters use the hydrant in front of your house to extinguish the flames before any of your neighbours’ homes are ever at risk of catching fire.