Fire investigators determine the origin and causes of fires.

Fire investigators work on cases where the cause of a fire may be arson (intentional fires) or criminal negligence (neglect of the property). Investigators take photos of fire damage. They examine fire sites and collect evidence of possible causes of fires. Fire investigators test sites and materials to get the facts straight. For example, they test burn patterns and flash points. A flash point is the lowest temperature at which a fire will start.

Fire investigators interview witnesses. They gather information about the fire, including when it started and how it burned. They talk to property owners and building occupants. They sometimes order people to go to court.

Fire investigators analyze the evidence and try to determine the causes of fires. They use air sampling machines to detect gases, or use sniffing dogs. They check wiring to see if it was improperly put together. They keep records of known arsonists in their area. They compare the arson methods in new cases against the methods these arsonists have used in the past.

Investigators prepare reports of the results of their investigations. They have the authority to issue warrants and arrest suspects. They may also testify in court about fire cases.

Some fire investigators investigate their own fire departments. They search for neglect or violation of laws by employees. Some fire investigators educate the public, particularly children, about the dangers of fire.