Wildfire Origin and Cause Investigation - Part 2

In Part 2 of “Wildfire Origin and Cause Investigation,” we will continue to discuss the main points for the local fire investigator to focus on when conducting a wildfire investigation. Hopefully, last month’s article was an eyeopener for some local...


In Part 2 of “Wildfire Origin and Cause Investigation,” we will continue to discuss the main points for the local fire investigator to focus on when conducting a wildfire investigation. Hopefully, last month’s article was an eyeopener for some local investigators to expand their education. The topics we will cover this month will be fire cause determination and fire cause categories/ignition sources. Investigators should become familiar with NFPA 921 and NWCG Wildfire Origin and Cause Determination Handbook. These references will aid the investigator when conducting the investigation of a wildfire.

Fire Cause Determination

Remember, as fire investigators it’s our duty to seek the truth. The goal of any fire investigation is to establish the area of origin and establish the cause of fire using the scientific method. Ignition sources may be in the form of open flames, glowing embers, mechanical or electrical sparks, friction and chemical chain reactions. When determining the fire cause, the investigator must consider the conditions and circumstances that bring together the ignition source, fuel and oxidizer. Remember, if the fire was intentionally ignited, the ignition source may have been removed from the scene.

When the point of origin is identified, the investigator should look for indicators of the cause of the fire. When examining the fire scene for ignition sources, keep these few tips in mind. Always search the area systematically, look for items that do not belong in the area, interpret burn indicators correctly and do not get overwhelmed with a large fire. Learn to concentrate on small areas and filter out the background. The investigator should classify the cause according to the ignition source or human act related to the fire. A full list of fire cause categories and classifications are listed in NFPA 921 and the NWCG Origin and Cause Handbook. Let’s briefly discuss the categories and classifications that are associated with these types of fires.

Fire Cause Categories/Ignition Sources

Incendiary: The incendiary fire is intentionally or maliciously set in which the person knows that the fire shouldn’t be ignited. These fires are often set in more than one location and are located in frequently traveled as well as remote areas. When conducting the examination at the point of origin, look for matches, lighters, or time-delay devices as shown in Photo 1. When searching for time-delay devices, look for rubber bands, matchbooks or cigarettes. The firesetter may use a number of ignition sources that include the hot set, direct set and remote set. The hot set is when the firesetter uses an open flame and starts the fire immediately. The direct set is hand carried and placed in the area. The remote set can be projected or thrown to another location. The Molotov cocktail is an example of a remote set.

Lightning: Lightning is discharged static electricity. Lightning is a frequent cause of wildfires in forested areas and can strike trees and power lines. Lightning strike indicators are scars, blowholes or glass-like clumps called fulgurites. These types of fires may smolder undetected for days or weeks before becoming an active wildfire. The investigator should conduct witness interviews if possible to determine if any storm or lightning activity was seen prior to the fire. If the area or point of origin is located in a remote area and no human activity is observed, it is possible that a lightning strike has occurred. Remember to check with the weather service and review the lightning data for at least the 15 days prior to the fire.

Campfires: Campfires are used for cooking, light, warmth and ceremonial purposes. Indicators of a campfire site are a circle of rocks within the burned area. The campfire may have seating or logs around the circle of rocks and unused fire wood. Remains of a tent and discarded food containers may be in the campsite, as shown in Photo 2. The investigator should determine if the campsite is located in an approved location. Remember, many campsites and parks have restrictions on the use of campfires and a permit is required.

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