Written by Katherine Steck-Flynn
The Fire
Arson
investigation starts with the fire itself. To create and sustain a
fire three factors must be present. The three factors are known as
the fire triangle (Peige ed., 1977). The fire triangle consists of
oxygen, a fuel source, and heat. In most cases the percentage of
oxygen concentration must be above 16% (Peige, ed., 1977). The fuel
may be any flammable substance. The heat source needs only to match
the ignition temperature of the fuel.
In
a fire involving arson the arsonist will have tampered with one or
more of the factors in the fire triangle. The arsonist may increase
the fuel load by introducing flammable material or by adding
accelerants such as kerosene, gasoline or alcohol (French, 1979) The
arsonist may increase the oxygen content of a structure by opening
windows or punching holes in ceilings and walls (French, 1979) Fire
will follow the highest concentration of oxygen to its source. By
ventilating a structure at the top and starting a fire at the bottom
of the structure an arsonist can cause the fire to race upward
through the structure. The fire will rapidly involve the whole
structure rather than be confined to one room.
An
arson fire involves the introduction of a heat source that can be as
simple as a match or as complex as chemicals with very low ignition
temperatures (Battle, 1978). By definition a fire is considered an
arson fire when all other accidental caused have been ruled out. To
say that the cause of a fire was arson and therefore deliberate, the
investigator must have sufficient evidence the one of the factors in
the fire triangle was tampered with.
The Fire Fighters
Arson
investigations start with the observations of the fire fighters who
respond to the scene. The fire fighters may not see any obvious signs
of arson but may get a feeling that the fire is not behaving normally
(Kennedy, 1977) (Battle , 1978) ( French , 1979).
There
may be obvious signs of arson such as multiple points of origin or
the presence of accelerants. What ever it is that raises the
suspicions of the fire fighters at the scene it is their observations
that initiate an arson investigation.
At
this point the investigation deviates from the procedures used in a
normal criminal investigation. In a normal criminal investigation
interviewing witness is usually done after the physical evidence is
processed (Osterburg & Ward, 2000). In an investigation of a fire
where arson is suspected the investigator starts the interviewing of
witness and fire fighters immediately (Kennedy, 1977). It is
essential for the investigator to interview the fire fighters who
were the first to arrive at the fire and those who fought the fire.
Fire will often destroy evidence of arson. As well, the water and
chemical foam used by the fire fighters may destroy evidence. The
first fire fighters on the scene may have noticed evidence that may
not exist by the time the fire is extinguished. The arson
investigator will ask specific questions aimed at revealing
suspicious conditions with in the structure and around the fire
scene. The arson investigator will ask the following questions.
What
was the color of the smoke? Different substances produce smoke in a
variety of colors (Lane, 1992). The color of the smoke can indicate
what is burning. The investigator can then determine whether a
particular substance would normally be found with in the structure.
For example, gasoline produces a yellow or white flame with black
smoke (Lane, 1992). Wood produces a yellow or red flame and grey or
brown smoke (Lane, 1992). If a burning wooden house is producing
thick black smoke this could indicate the presence of gasoline. A
large amount of gasoline being stored in a house is unusual and
raises the suspicion that gasoline was used as an accelerant.
Were
there inoperative hydrants, standpipes, alarm systems or sprinkler
systems? If there were the investigator will direct plumbing and
other trades experts to examine the systems for signs of damage
(French, 1979) (Kennedy, 1977).
What
was the condition of the doors and windows? Signs of forced entry can
indicate an actual break and enter or indicate a staged scene. Doors
and windows propped open could indicate an attempt to ventilate the
building allowing the fire to spread through out the structure. Doors
and windows that have to be forced open could indicate an attempt to
hinder the fire fighters. Doors and windows that have been blocked
out could indicate an attempt to conceal the fire until it is fully
involved (Peige, ed. 1977)
Was
there anything strange about the way the fire was burning? Rapid
spread of a fire can indicate the use of accelerants. Multiple points
of origin, flashes and explosions can also indicate accelerants or
incendiary devices (French, 1979) (Peige, ed., 1977)
Where
there any familiar faces at the scene? It is possible that the fire
fighters have seen the same person in the crowd at several fires.
Some arsonists like to watch the fire or help the firefighters. If
the fire fighters do notice the same person at several suspicious
fires the investigator must try to interview this person as so as
possible (Kennedy, 1977).
Did
the structure contain business equipment or household items normally
expected to be present?
The
absence of normal household items or business equipment can indicate
that they were removed before the fire started. Removal of these
items can indicate that the fire was planned. Removal of sentimental
items such as baby picture, school records and valuables can indicate
a planned fire. Evidence of pre-planning a fire gives the
investigator excellent proof of intent to commit arson.
