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Fire Investigation – Procedures

July 15, 2011

We’ve all seen it on TV news.  The reporter is covering a fire story and indicates that the cause is “under investigation”.  So what is it that fire investigators do?  On TV the CSI people solve every case in one hour or less.  Is that reality?  Not really.

Washington State law tasks fire agencies to determine origin and cause of a fire.  Origin is the point where the fire started.  Cause has three parts:  the ignition source, the first fuel ignited and the act that brought them together.  Once the fire investigator can document those four things, he’s done.  Sounds simple, right?  Remember, unlike the standard crime scene, a fire scene has also had much of the evidence destroyed by fire.  So fire investigation has an added degree of difficulty over standard crime scene investigation.

Consequently fire investigators follow procedural checklists that originate from a number of places.  For starters, the Supreme Court of the United States has determined that to be admissible in court, a fire investigation must follow scientific method.  If a fire investigator cannot prove that standard scientific method was followed, her testimony can be thrown straight out of court.  Secondly, we must provide all the protections against unreasonable search and seizure guaranteed by the fourth amendment of the Constitution.  Lastly we have to understand the burden of proof demanded by the courts.  In a criminal case (where someone needs to go to jail for the crime of arson) we must prove our case beyond a reasonable doubt.  In a civil case (one party is suing another to pay for costs) the burden of proof is only a preponderance of evidence (a much easier burden of proof to meet).  Since we never know when we roll up on a fire what type of case this will be, we tend to pursue proving our case beyond reasonable doubt just to be safe.

Those three elements drive a lot of fire investigation procedures.  Our investigators normally start by securing the scene, interviewing witnesses, taking photos and recovering any evidence that may get damaged by the fire.  Once those things are addressed we start sifting through the ashes, reconstructing the scene and drawing scale sketches of what we’ve found.  Normally we look for the origin first and the elements of cause should be located around the origin.  Using scientific method, our investigators build hypotheses based on the facts they collect and then test them out.  If a hypothesis does not stand up to rigorous examination, it gets discarded and another hypothesis is built.  In some cases multiple hypotheses have been built and discarded because the facts didn’t bear them out.  When the facts support a final hypothesis, we publish that as our report on the origin and cause of the fire.  Obviously this can take some time but we don’t want to discuss a hypothesis until it has been proven out by facts.  Our final report has to be an accurate description of what we did and the findings that resulted.

Next time out, we’ll discuss how that investigation report is used.

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