BURN PATTERN RECOGNITION FOR FIRE ORIGIN ANALYSIS
Charles C. Roberts, Jr., Ph.D., P.E.
(Published in Insurance Adjuster Magazine, July 1987)
Determination of the origin of a fire is a necessary part of an investigation. Burn patterns at the loss site typically aid in the determination of the fire origin. The following are some thoughts to consider when
assessing the origin of a building fire based on burn patterns.
The concept of low burn is often invoked as a way to determine the fire origin. The low burn area usually is the fire origin since the fire typically travels upward in a V shaped pattern. Figure 1 shows a low burn area where severe damage has occurred characterized also by deep charring of the wood. The well known phenomenon, that hot gases from a fire rise, accounts for the fire spreading towards the upper portion of the building (V pattern). In Figure 1 the pattern is typical of a single origin at the bottom of the V.
Figure 2 shows multiple V patterns in a building which is often construed to be multiple origins. Since multiple accidental fire origins are unusual, suspicion of arson is often opined. Other alternative possible causes should be investigated thoroughly. During one fire, the fire department began to fight a fire in a residential building until a substantial natural gas leak occurred. They were withdrawn from the scene until the gas could be turned off. As a result of holes chopped in walls and roofs by the fire fighters, the fire caused severe burnouts in several locations looking like a multiple origin fire.
The common characteristic of fire origins shown in Figures 1 and 2 are the lack of pattern distortion from other influences such as wind. Figure 3 shows burn pattern distortion from wind. During windy conditions, a fire can easily spread downwind yielding a distorted V pattern. In some instances it is tempting to place the origin in the vicinity of the center of the burn (False origin Figure 3). If high winds were present, searching for an origin upwind from the center of damage may be fruitful.
Structural interactions with the fire can also result in a burn pattern distortion and false origin analysis. Figure 4a shows a fire starting above the doorway. As the fire progressed, it weakened the roof structure causing a collapse, resulting in the fire dropping to a lower level (drop down fire). This can result in a false origin determination as shown in Figure 4b.
Flammable materials located in a building can cause distortion to a fire burn pattern. In Figure 5 a fire started to the right of the main entrance. However heat transfer from the fire ignited flammable materials nearby causing a low burn area that can be mistaken as the origin.
In other instances the fire may be so devastating that burn patterns may be inconclusive as far as the origin is concerned. Figure 6 shows a severe burnout of a building with no discernable pattern pointing to the origin. In these instances some other means may be required to find the origin.
Burn pattern recognition is quite useful in analyzing the origin of building fires. Thorough examination of burn patterns is necessary to avoid some of the pitfalls of false origin determinations.