Other Laboratories and Technical Experts
By B. Wesley Sherman
Professor of Electrical Engineering
University of Missouri, Columbia
During the course of your investigation you may find that you need to
go beyond the criminal investigation laboratories to determine the cause
of an accidental fire. There are several reasons for this. For example,
you may need to use expertise not normally needed in criminal investigations.
Examples would be those cases involving failures in vehicles, household
appliances, commercial equipment or other systems. Considerable work has
been done by civilian scientists and engineers to analyze and document such
product and system defects. Usually, these experts are pleased to cooperate
with local and federal agencies to determine, record and disseminate the
desired information. Many of these investigators also are willing to respond
to requests to seek new information related to fire investigation.
As an example, consider that it has been desired to know details about
the behavior of electrical circuit breakers when subjected to the conditions
in a fire. The ordinary inverse-time circuit breaker used in most residences
and offices has two mechanisms that cause it to trip. One is the magnetic
field resulting from the electrical current, and the other is the heat caused
by that same current. The magnetic trip is for rapid, extreme overloads,
while the heat-initiated trip is for long-term overloads that are not extreme.
The heat sensitive mechanism can be actuated by the heat of the fire in
addition to the intended electrical current. Furthermore, the fire can trip
the breaker, even if it is already in the off position. Often, an investigator
needs to know whether the breaker tripped from an electrical overload, or
from the heat of the fire. Also, the investigator usually needs to know
what position the breaker was in before the fire.
Some investigators have developed the ability to determine the above
information in many important situations. X-ray examination of the breaker
after the fire can reveal the positions of its internal parts, even though
the hand-operated lever and other external indicators have been destroyed.
Movements of the internal mechanisms during the fire are related to the
prior positions and to the cause of tripping. By testing and experimenting,
investigators have learned in many cases to interpret the results of x-ray
examination, and to obtain the desired information. Figure 1 shows x-ray
images of circuit breakers examined in the above manner.
Similar studies have been performed to obtain fire-related information
from kitchen appliances, entertainment centers, lighting fixtures, vehicle
sub-systems, heating and air conditioning systems, metallurgical interactions,
and many other specialties.
An accidental fire may result from the configuration of an overall system
rather than from a defect in an individual component. A simple example would
be the use of a fuse that is too large for a particular application. If
a fire results, there may be no single component of the system that would
exhibit evidence of a defect. The expertise of a systems designer may be
required to accomplish the proper evaluation.
At times, it is appropriate to bring a technical person from the laboratory
to the fire scene. If the investigator believes, for example, that an appliance
may be the cause of the fire, he or she must always allow for the fact that
the appliance may be determined by the expert to be free of involvement
in the cause of the fire. In that case, it may be necessary to continue
work at the fire scene. If the scene has been released, it may not be possible
to continue the analysis. In such cases, it is often wise to bring the expert
to the scene, so that work may continue if the suspected appliance is found
to be free of involvement in the cause of the fire.
Locating Technical Assistance
Locating the appropriate expert is a normal part of the investigation
process. The various professions have national and state associations that
provide services ranging from training and certification to technical publication
and political lobbying. However, few of the professional societies have
reason to maintain information specifically related to fire investigation.
Exceptions would be specialized organizations such as the International
Association of Arson Investigators. Also, for several reasons, some experts
choose not to advertise. The fire investigator should be willing to make
an appropriate effort to locate the best technical assistance for a particular
The most direct way to locate an expert may be to talk to someone who
has solved a similar problem. The information pool would include other investigators,
insurance companies, state and local departments of public safety, fire
and police departments, colleges and universities, the internet, and other
technical experts. Some investigators have identified suitable experts by
reviewing pleadings, depositions, and transcripts of litigation. It is the
responsibility of the investigator to be sufficiently creative to locate
the needed technical assistance. In any event, we strongly suggest that
you locate and develop rapport with several technical experts prior to having
the need in a critical investigative situation. Some suggestions of the
types of technical experts to locate are, Electrical Engineers, Mechanical
Engineers, Structural Engineers, Metallurgists, etc. If you develop these
technical contacts in advance, you will find that your investigative efforts
can be focused on solving the case.
Reprinted with permission from the author.