Do you know what a detective does? They try to figure out what happened when something bad or wrong happens. Fire investigators are like detectives, but they try to figure out what started a fire and how it happened.
When a fire happens, fire investigators go to the place where the fire happened and take a look around. They look for clues like burned things or things that were hot. They might also take pictures or talk to people who saw what happened.
Once they have all the clues, fire investigators try to figure out what happened. They might use special tools like thermometers or cameras to help them. They also use things called "interviews" to ask questions to the people who were there.
After they figure out what happened, they write a report to tell other people what they found. That way, everyone will know what happened and how to keep the same thing from happening again.