Have you ever heard a fire alarm that goes "beep, beep, beep"? That alarm is there to warn you when there is a fire in a building. But sometimes, when a fire is really big, one alarm is not enough. In those cases, firefighters might use multiple alarms.
Imagine you are sitting in a big room with lots of toys. Suddenly you smell smoke and see fire coming from one corner of the room. You quickly run to the door and tell your mom to call the firefighters. The firefighters come and use their hoses to put out the fire. But, sometimes the fire can spread so fast that one fire truck is not enough to put it out. That's when firefighters call for backup and more trucks come to help.
When a fire is too big for one firefighter, all the firefighters in the area will come to help. They will use their trucks and tanks to bring lots of water to the fire. They will use big hoses, buckets, and even helicopters to pour water on the fire from above.
To help keep the firefighters organized, they use something called a "multiple-alarm fire." A multiple-alarm fire is a way to tell the firefighters how big the fire is and how many people they need to help put it out.
For example, a one-alarm fire might mean that one truck and four firefighters are needed. A two-alarm fire might mean that two trucks and eight firefighters are needed. A three-alarm fire might mean that three trucks and twelve firefighters are needed, and so on.
So, when you hear about a multiple-alarm fire, it means that there is a really big fire, and lots of firefighters are working hard to put it out. They need many people and trucks to stop the fire from spreading, to keep everyone safe, and to save the building.