Investigative Challenges in Todays Wildfires

The wildfire season started early in 2002. Colorado experienced significant wildfires in early April at altitudes up to 10,000 feet. Snow is usually still falling at this time in the mountains and foothills, but low snow pack and warm temperatures led to an early wildfire season.

As portions of the U.S. experience extreme drought with an uncertain future, for the next few seasons we can expect to see an increase in the amount of wildfires. According to the National Interagency Fire Center in Boise, Idaho, in 2002 there were 73,457 reported wildfires in the U.S. with over 71,847 acres burned. With wildfires destroying hundreds of homes in the western United States last year, determining the cause of the wildfires has become an important issue for many insurance companies.

In some cases, the wildfire started in a structure and then spread to the adjacent forest. A standard structural investigation can usually reveal the cause if the fire started in a home; however, an added component is then to determine how and where the fire was communicated to the forest or adjacent structures.

Wildfire investigation presents several unique challenges for even the most seasoned fire investigator. Many fire investigators “learn the ropes” and have the most experience on structure fires and are intimidated by seeking an origin and cause in the outdoor arena. While some parallels can be drawn between structural and wildfire investigations, investigators have to be well versed in several different approaches.
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Where does one start when investigating a 50,000 acre wildfire? A systematic approach will help narrow down the search area. A good place to start is with dispatch information. Where was the fire first reported? Who was the reporting party and what did they see? Information from first-responding law enforcement or fire personnel can often assist in determining a general area of origin. Other factors to be explored include: detailed weather information such as wind speed, wind direction, relative humidity, fuel moistures, spread components, flame length, energy release components, ignition components, and the burn index. Add to this information the general topography such as aspect of the slope, angle of the slope, and fuel types, and we can further narrow down the area of origin. Additional analysis, consisting of “running fires” such as those that move rapidly in one direction due to wind and or topography versus a “backing fire,” which is pushed back by wind or topography, assists in origin determination. Field investigators use colored flags to indicate running and backing fires. This process often leads them back to the area of origin.

An experienced investigator will also examine char patterns on trees or fences, angled or bent grass and shrubs, cupping of burned-out trees, and staining or soot on rocks. The area of origin is then sufficiently narrowed down to conduct a search for cause. All of this is supplemented by standard practices such as detailed photography, extensive interviews, and, when possible, aerial observations. Mapping the extent of the fire and overlaying it on a topographic map, as well as analysis of some of the above items, will often pinpoint the area of origin.

Once an area of origin is identified, a grid pattern has proved effective in finding the cause. One method is by using different colored string to grid out the area. An overall map of the grid and findings is then initiated. Each section is meticulously searched for possible ignition sources. The drawback to this process is that it can be very labor-intensive; however, in multi-structure losses, the stakes are equally high. Common ignition sources include: lightning, a matchbook, cigarette lighter, welding or cutting operations, sparks from train or vehicle brakes, catalytic converters, and electric fences. The most popular ignition delay device is a cigarette wrapped with stick matches. Despite the widespread damage; through careful sifting, one can often find a cigarette, matchbook, or other ignition source. In fact, fingerprints have been obtained on such items even after some heat damage. Additional causes include human factors such as ditch burning, slash burning, welders’ torches and unattended campfires. Detailed and persistent interviews will often assist in these cases. In agricultural areas, hay piles have been found to spontaneously combust, causing a fire. One case in Wyoming even revealed that a meteorite started a fire.

Wildfire investigation can be frustrating to a fire investigator whose experience has been limited to structural fire investigation. Additional training is available from the U.S. Forest Service. Several excellent texts such as Kirks Fire Investigation (5th edition) by Dr. John DeHaan and IFSTA‘s Wildland Firefighting and Wildfire Tactics and Strategy by Donald Perry were used as references for this article and can provide some basic knowledge. This should be supplemented by supervised field investigations. Parties interested in obtaining a comprehensive wildfire investigation should seek individuals and firms who have investigators who are well-versed in this arena.


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