Fire investigation, sometimes referred to as origin and cause investigation, is the analysis of fire-related incidents. After firefighters extinguish a fire, an investigation is launched to determine the origin and cause of the fire or explosion. Investigations of such incidents require a systematic approach and knowledge of basic fire science.
Investigating fires
The difficulty of determining whether arson has occurred arises because fire often destroys the key evidence of its origin. Many fires are caused by defective equipment, such as shorting of faulty electrical circuits. Car fires can be caused by faulty fuel lines, and spontaneous combustion is possible where organic wastes are stored. A fire investigator looks at the fire remains, and obtains information to reconstruct the sequence of events leading up to the fire.
One of the challenging aspects of fire investigation is the multi-disciplinary basis of the investigator's job. As fires can be caused by or involve many ignition sources and fuels, an individual with expertise in fire chemistry should investigate the incident. For example, if there is a gas appliance at the origin of the fire, an investigator should know enough about appliances to either include or exclude it as a possible cause of the fire. Fire investigators sometimes work with forensic engineers, such as forensic electrical engineers when examining electrical appliances, household wiring, etc.
In the United States, fire investigators often refer to NFPA 921: Guide for Fire and Explosion Investigations (National Fire Protection Association). Also, Kirk's Fire Investigation by David J. Icove and Gerald A. Haynes has long been regarded as the primary textbook in the field of fire investigation.
Conducting investigations
The main steps of a fire investigation include:
Arrive at the scene
Ensure safety of crime scene
Secure the area
Investigate the scene
Evaluate external structure
Evaluate interior structure
Determine point of origin
Document the evidence
Sample and tag evidence
Sketch the scene and damage
Photograph evidence
Conclude the investigation
Finish necessary documents/reports
Interview necessary parties
Present evidence
Fire investigators conduct their investigations using a systematic approach utilizing the scientific method, including the following: When arsonists attack, there is very rarely much evidence left at the scene. However, arsonists usually use accelerants to speed up a blaze. Forensic scientists use technologies to heat samples taken from the scene causing any residue to separate. This sample is then analyzed to determine the chemical structure. Scientists also use other tests such as using liquid nitrogen gas to trap residue which are then analyzed using gas chromatography. The investigator:
Receives the assignment and responsibilities
Plans the investigation and assembles tools, equipment, and personnel
Examines the scene and collects data
Collects, tests, evaluates, and documents evidence
Applies the scientific method to analyze the information obtained
Depending on how much evidence is present, an investigator can use different approaches. Two techniques include process of elimination, or disregarding the causes that the evidence deems not possible. The second is to start investigating the most probable cause first until it is ruled unlikely.
Spoliation
Spoliation is the destruction or alteration of evidence through intention or ignorance. The mere act of extinguishing a fire can destroy potential evidence of arson or what is also known as an "Incendiary fire." Firefighters are educated that the stream of their fire hose or the use of a Pike Pole can destroy evidence and efforts are made to do what is required to extinguish the fire, while not destroying clues to the fires' origin. By taking steps before the investigation starts, destruction of evidence can be avoided. Investigators are encouraged to set barriers and secure the area. This allows for control to be taken over the crime scene and limits the chance of an investigation being compromised. Investigators then document any evidence seen at the crime scene or on the victims (clothes, burns, etc.) While looking for evidence, any findings that impose a threat to evidence, such as excessive use of fire-suppressing chemicals, unusual movement of handles/knobs, and changed position of evidence should be reported.