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
Figure 1
Figure 2
Figure 3
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They were withdrawn from the scene until the gas could be turned off.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.
Figure 4a
Figure 4b
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.
Figure 5
Figure 6