Scientific processes used to determine cause and origin of fires

June 4, 2013 By    

NFPA 921 sets the standard for scientific-based investigation of fires and explosions. It is the foremost authority for reaching opinions regarding fire and explosion origin, cause and responsibility.

Ultimately, private and public sector investigators utilize NFPA 921 for purposes ranging from basic fire investigation to insurance claims investigations and litigation preparation.

In conducting a fire or explosion investigation, authorities are looking to classify the cause of the fire by looking at the source and form of ignition, the first materials ignited and factors contributing to ignition. After such evidence and data are collected, the investigators will classify the cause into one of four categories: accidental, natural, incendiary and undetermined.

The first three classifications are self-explanatory. Accidental fires are not the result of deliberate or intentional actions, but also can encompass intentionally ignited fires, such as brush or trash fires, which spread uncontrollably. Natural fires occur without human intervention, traditionally associated with acts of God, such as lightning, wind or earthquakes. Incendiary fires are caused by a person’s intentional conduct and are predominantly criminal in nature, although a fire caused by a person’s negligent or reckless conduct can sometimes be classified as incendiary.

Ultimately, a fire determined to be in the first three classifications is the result of the investigators’ cause and origin hypothesis being directly supported by the data and physical evidence gathered during the investigation.

The fourth classification, however, is easily misunderstood. The official NFPA 921 definition for an undetermined fire is “whenever the cause cannot be proven to an acceptable level of certainty.”

If a fire is found to be undetermined, it generally means the fire simply has not been investigated; the investigation is ongoing and no cause has been determined to date; or after a full investigation the ultimate cause of the fire was not proven to an acceptable level of certainty.

An investigation conducted pursuant to NFPA 921 Chapter 18 requires investigators to identify the “materials, circumstances and factors that were necessary for the fire to have occurred.” This includes locating all devices, appliances or equipment involved in the ignition and locating the presence of a competent ignition source, the type and form of the material first ignited, and the failures, circumstances or human actions that came together to allow the fire to occur. Basically, investigators are looking for valuable evidence that proves what caused the ignition and the materials ignited.

But if after a full investigation, investigators are unable to identify or locate physical evidence of the source and form of the ignition or the first materials ignited, the cause must be classified as undetermined. A lack of physical evidence leading to an “undetermined” classification can occur for a couple reasons.

First, the fire or explosion can destroy valuable evidence of ignition source or first ignited materials, which in turn leads to a lack of data needed to classify the incident.

Second, valuable physical evidence can be destroyed at fire and explosion sites due to spoliation – the intentional or accidental destruction of evidence due to mishandling of the accident scene. Spoliation can occur for a number of reasons, including allowing untrained individuals onto an accident scene. Ultimately, NFPA 921 sets basic procedures to prevent the unnecessary spoliation of valuable evidence.

So ultimately, although unknown to investigators, a fire or explosion could be caused by a person’s intentional conduct or an act of God, but without the proper physical evidence pinpointing the source of ignition, first fuel and other vital facts, investigators may be required to classify the incident as undetermined.

As difficult as fire and explosion scenes can be, the origin and cause of the explosion can be determined many times with sufficient certainty. To get to this result, the site must be protected from spoliation or tampering. So keep this in mind if you have a case awaiting inspection. Keep the scene pristine.

John V. McCoy is with McCoy Leavitt Laskey LLC, and his firm represents industry members nationally. He can be reached at 262-522-7007 or

This article is tagged with , , and posted in Current Issue

Comments are currently closed.