Lack of science is behind many false arson cause and origin investigations
Arson
investigation, unfortunately, is a field where junk science has been the rule
rather than the exception. A large body
of cause-and-effect mythology has developed in fire investigations over the
years. As far back as 30 years ago we
have been arguing that the opinions stated by many fire investigators were not
based on science and they were in fact false.
Due to these faulty opinions, many people were convicted of arson and
many people lost their home and their livelihood. Some people have allegedly been put to death
having been convicted of arson, based on the same old cause-and-effect
mythology.
Through the 1980s, proponents (including ourselves) of a science-based approach to arson investigations waged an uphill battle, finally winning a major victory in 1992 when the National Fire Protection Association (NFPA) published its Guide for Fire and Explosion Investigations (NFPA 921). NFPA 921 would subsequently become the bible in fire and arson investigations.
Through the 1980s, proponents (including ourselves) of a science-based approach to arson investigations waged an uphill battle, finally winning a major victory in 1992 when the National Fire Protection Association (NFPA) published its Guide for Fire and Explosion Investigations (NFPA 921). NFPA 921 would subsequently become the bible in fire and arson investigations.
Prior to NFPA 921, the fundamental
principles for determining the causes of fires did not involve science per se,
but rather experience-based hypotheses that were not tested to determine their validity.
This process, known as “negative
corpus,” relied on a process of elimination rather than supporting evidence or
scientifically supported conclusions, and some investigators feared that a
science-based approach would establish criteria of proof that would be too
difficult to meet. So, they fought NFPA
921.
The Daubert v. Merrell Dow Pharmaceuticals decision was handed down in
1993, where the U.S. Supreme Court made judges the gatekeepers of expert
testimony. The ruling said that judges
have to determine if expert testimony is reliable, and that using a methodology
that has been peer reviewed, published, and accepted was part of that
reliability test. So in cases that
included fire investigations, courts began gravitating towards NFPA 921, a consensus
document from a group of leaders in the fire investigation community. The U.S. courts began referring to NFPA 921
as the “standard of care” for evaluating expert testimony regarding fire
investigations.
An organization called the Innocence
Project [which works to exonerate the wrongfully convicted] has taken an
interest in arson cases. They are going
back and evaluating the science or lack thereof in investigations and comparing
it with what’s available today. They
estimate that between 200 and 400 individuals may have been wrongly convicted
of arson based on false evidence and false expert testimony using
non-scientific methods.
We
are also very gratified to see state legislatures now trying to reverse some of
the wrongs committed over the years as a result of these false opinions and
wrongful convictions. In this blog lack
of validity of common myths is reviewed, and new forensic engineering analysis
techniques discussed consistent with the NFPA
921.
The COMM. ON IDENTIFYING THE NEEDS OF THE FORENSIC SCI.
CMTY. ET AL., published the report entitled NAT’L RESEARCH COUNCIL OF
THE NAT’L ACADS.,STRENGTHENING FORENSIC SCIENCE IN THE UNITED STATES: A PATH
FORWARD (2009). Therein, the report
stated the following regarding the fire investigations:
By contrast, much more research is needed on
the natural variability of burn patterns and damage characteristics and how
they are affected by the presence of various accelerants. Despite the paucity
of research, some arson investigators continue to make determinations about
whether or not a particular fire was set.
However, according to testimony presented to the committee,[1] many of the rules of
thumb that are typically assumed to indicate that an accelerant was used (e.g.,
“alligatoring” of wood, specific char patterns) have been shown not to be true.[2] Experiments should be
designed to put arson investigations on a more solid scientific footing.
In
the early 1990’s, fire investigators relied heavily upon the teachings of their
mentors regarding the nuances involved in interpreting incendiary indicators. Access to controlled burn experiments and
other practical guidance regarding the science of fire behavior was limited. At the national level, the NAS Report notes the
prevalence of apprenticeship training across forensic disciplines, finding that
reliance on “apprentice-type training” and a “guild-like structure” works
against predictability. (NAS Report at 15-16.) Similarly, the knowledge levels
on which fire investigation practices were based at the time were “extremely
variable” due to the “one-on-one training that dominated.” While scientific papers and textbooks
describing some of the “modern” fire science principles existed in the early
1990’s, it is difficult to determine how widely those materials were disseminated,
or whether they were understood and accepted by fire investigators at the time.
Perceived Gap in Understanding Between Fire Scientists
and Fire Investigators
Many
are concerned about perceived differences in understanding of fire indicators
between the scientists and engineers who study principles underlying fire
indicators, and the state and local professionals who respond to and
investigate fires. One challenge is the
lack of science education on the part of many fire investigators. Though this dynamic is changing as younger
classes of investigators gain exposure to college coursework in chemistry and
physics, most active investigators do not have scientific backgrounds.
Elimination of Accidental Causes
A
critical component of successful fire investigation is the elimination of accidental
causes. The elimination of any single
cause requires an investigator to use his or her judgment, and to request
outside assistance when necessary. For example,
when considering whether a child could have set the fire in a case,
investigators may conclude that the possibility was remote considering the ages
of the children, the fact that no lighters were found near them and that a
child’s gate blocked the bedroom doorway.
This is the sort of judgment that fire
investigators typically must engage in during the course of an investigation. Investigators would be required to make a
similar judgment call today if the same facts were presented.
However,
other components of assessing accidental causes have been assisted by
developments in science and engineering over the last two decades. For example, scientists and engineers have
created methods that allow investigators to conduct a more thorough review of
possible electrical malfunction as a point of origin. In the early 1990’s, investigators routinely
checked for shorts in the line after “pulling” the electrical meter for the
safety of those on the scene, in accordance with the safety requirements of
NFPA 921. (See NFPA 921, 1995 edition at 10-2.4.) If there were no shorts in the line and no
evidence of appliance malfunction, investigators concluded that the cause was
not attributable to electrical malfunction.
Today’s
investigators have additional tools at their disposal. For example, investigators
can use the process of arc mapping (See
2011 edition of NFPA 921) to determine
a fire’s possible point of origin. Many
local investigators are aware of the arc mapping process and often consult
electrical engineers for assistance.
Pattern Indicators
As
previously stated, the value of various incendiary indicators and the manner in
which they are identified has changed since the early 1990’s. Experts have identified indicators that were
present in the Texas arson cases of Willingham (who was executed in 2004) and
Willis (who was freed in 2004) that have since undergone extensive scientific testing
and experimentation.
Such testing has
provided scientists with a better understanding of the limitations of the
indicators. Many of these indicators may
be present in arson cases where accelerants are used, thus requiring an
investigator to use the scientific method as expressed in NFPA 921 to conduct a
systematic review. The discussion below does
not examine every indicator used in the fire investigators’ reports but rather
includes illustrative examples applicable to all arson cases.
Excerpts from fire scene reports and trial
testimony, though inherently incomplete, provide a sense of the investigators’
understanding of incendiary indicators at the time of trial. The question of when, why and how certain
limitations should be applied to incendiary indicators is the subject of
ongoing study by the fire science community.
The classic V thermal damage pattern is
used by analysts to determine the origin of the fire, the base of the V being
the likely origin of the fire
1. V-Pattern as Indicator of Origin
Family room
V-Pattern
A Fire Marshal’s report discusses “V-patterns” as an indicator of fire origin. The report states:
The burn pattern
on the east and west wall of the hallway disclosed a gradual climb in a 45
degree angle toward the south end and clearly showed a “V” pattern. This “V” pattern is an indicator that the fire
originated on the floor near the north end. The north end area of the floor disclosed that
the fire had burned through the tile blocks and caused charring of the wooden
floor underneath. The burn pattern on
the floor and “V” burn patterns on the walls is an indication that a fire
originated at the north end area of the center hallway.
The Fire
Marshal also testified regarding “V” patterns as follows:
The photograph
that sees the V pattern debris, that’s Exhibit No. 23. The one that tells where
the V is, that’s possible origin of the fire.
In
the early 1990’s, many fire investigators based their conclusions of origin in
part on the theory that a “V-pattern” on a wall points to the origin of the fire.
For example, the 1995 edition of NFPA
921 4-17.1 stated: “the angled lines of demarcation, which produce the “V”
pattern, can often be traced back, from the higher to lower levels, toward a
point of origin. The low point or vertex
of the “V” may often indicate the point of origin.” NFPA 4-17.1 (1995 edition).
Scientists
now know that the “V-pattern” simply points to where something was burning at
some stage of the fire, not necessarily the origin.
V pattern suggests a fire origin at the
red arrow in the vicinity of a stove top. There is some drop down burning
debris as shown by the green arrow.
2.
Pour
Patterns
A
Fire Marshal testified as follows regarding his interpretation of pour patterns
in the home he investigated:
So this area
right here are what I call burn trailers. Burn trailers is like a trailer, you
know, like a little path, a burnt path. A
pour pattern, which is a pattern like somebody put some liquid on the floor or
wherever and, of course, when you pour liquid, then it creates a puddle. Liquid creates puddles. When it rains you get
puddles. When the baby drops its milk, you
create puddles. If you ever drop a coke,
you create puddles. All this area has
that, has the burn trailer pour patterns and configurations. This area right
here, which is right here almost in front of this bed is deep charred. The floor, it didn’t burn through the floor,
but it burned the three layers of the floor. And a pour pattern and trailer is an
indication that somebody poured something, you know, either going in or out.
All fire goes
up. All water goes down. Or any liquid goes down unless man changes the course.
Another
Fire Investigator also testified regarding his interpretation of pour patterns
in another case:
It appears to be
burned areas resembling how a liquid would have run and burned on that surface.
(Answer in response to a question regarding irregular floor patterns.)
“I have never
run across that, no, sir.” (In response to the following question: “Now, in
your experience, training, and your reading publications to keep up-to-date,
have you or have you not heard of the phenomenon that radiation can cause
irregular patterns?”)
“That’s
correct.” (In response to counsel’s assertion that “fire burns up, not down.
In
the early 1990’s, many fire investigators reasoned that fire moves upward (at
least flames and hot gases do) and that carpet and flooring is difficult to
ignite. If one pours ignitable liquid on
a floor, the carpet burns away in an irregular path similar to the deposits of
the liquid. Thus,
it was often thought that pour patterns at floor level were “nearly proof
alone” that the fire was started with an accelerant. While such a fire could have been started with an accelerant
(see e.g., NFPA 921 1995 edition, 4-17.7.2) other phenomena of fire
behavior can also cause similar pour-like patterns.
For
example, when a fire approaches or surpasses flashover conditions, all of the
exposed carpet in the room will ignite. Synthetic carpets and pads melt or decompose
to liquid as they burn, producing highly irregular and unpredictable
patterns. The effect of ventilation
conditions, radiant heat, flaming and smoldering debris, and drop-down burning
from things like synthetic mattresses and bedding also affect the irregular
burn patterns.
The term pour
pattern implies that a liquid has been poured or otherwise
distributed, and therefore, is demonstrative of an intentional act.
Because fire patterns resulting from burning ignitable liquids are not visually
unique, the use of the term pour pattern and reference to the nature of the
pattern should be avoided. The correct term for this fire pattern is an irregularly shaped fire pattern.
The presence of an ignitable liquid should be
confirmed by laboratory analysis. The determination of the nature of an
irregular pattern should not be made by visual interpretation of the pattern
alone. See Figures below for examples of fire patterns on floors.
Fire Patterns on Floor Resulting from
Fully Developed (Post-Flashover) Fire in Full Scale Test Burn of Residential
Structure. Floor Was Carpeted and Room Had Typical Residential Furnishings; No
Ignitible Liquids Were Present.
Fire Patterns on Linoleum Floor Resulting
from Fully Developed (Post-Flashover) Fire in Full-Scale Test Burn of
Residential Structure; No Ignitible Liquids Were Present.
•
Holes
in the floor may be caused by glowing combustion, radiation or an ignitable
liquid.
•
There
is no justification that the appearance of large, curved blisters is an
exclusive indicator of an accelerated fire.
•
The
presence or absence of spalling should not, in and of itself, be construed as
an indicator of the presence or absence of a liquid fuel accelerant.
•
Inverted
cone patterns have been interpreted as proof of flammable liquid fires, but any
fuel source that produced flame zones that do not become vertically restricted
can produce inverted cone patterns.
Today,
fire scientists and investigators should have a better understanding of the
nuances of flashover conditions, including how to analyze their effects. Rigorous, ongoing training is the key to
ensuring that all investigators are knowledgeable about developments in the
scientific community’s understanding of the complex chemical and physical
phenomena involved in fires, including but not limited to the effects of
flashover.
3.
Low/Deep
Burning and Multiple Separate Points of Origin
A
Fire Marshal testified as follows regarding his interpretation of low/deep
burning and multiple separate points of origin:
And you got char burning, like for
example, this is the bottom here. It’s burned
down here at the bottom. That is an
indicator in my investigation of an origin of fire because it’s the lowest part
of the fire.
Multiple areas of origin
indicate—especially if there is no connecting path, that they were
intentionally set by human hands.
The first incendiary indicator is the
auto ventilation. The inconsistency of the fire going out of this window and
the fire going out of the door and this window here. That’s inconsistent with fire behavior. That’s
an indicator that it’s a possible incendiary fire. Okay. Puddle configurations, pour patterns, low char
burning, charred floor, the underneath burning of the baseboard, the brown
stains on the concrete, the underneath of the bed, because of the fire right
underneath the bed, puddle configurations in that area, and the total
saturation of this floor is indicated with pour patterns, because that’s all
I’m doing is looking at the facts, at the evidence.
A
Fire Investigator noted low burn as a significant indicator in another case as
follows:
Initially, when we had finished the
view of the exterior of the building and walked into the inside of the
structure, there were a couple of things that caught our attention right off.
First of all, the low burning on the walls almost to floor level.
The most highly significant would be
the low burning to the floor level on some of the walls, and the burn patterns
that I observed on the floor itself.
In my opinion, there was some type of
flammable liquid applied there. There
was no other fuel source there that would have indicated it would have burned
in that manner.
Low
burn patterns may be an indicator of accelerant, but scientific experiments
have also shown that radiant heat transfer causes low burn patterns, and that
the radiant heat of a fully involved room fire can be sustained to penetrate
floors deeply. Scientific testing has
also shown that ignitable liquids alone do not burn long enough to penetrate
floors deeply. Similarly, the appearance
of multiple separate points of origin may provide evidence that a fire was
intentionally set, but is often attributable to radiation and drop down
effects.
Burn Patterns on a Floor of a Room Burned
in a Test Fire in Which No Ignitable Liquids Were Used
Configuration is also of critical
importance when determining area of origin.
For example, fall down of something like curtains could cause an area of
low burning. That’s not an area of origin, but it can easily be mistaken
for one or be taken as ‘evidence’ of multiple fires. Another fire effect
that can cause low burning is radiant line of sight, which is responsible for
1/3 of the heat of a fire
Typically, the
difficulty with burn pattern interpretation happens when there is a strong
factor that tips the fire dynamics physics in a different direction that might
“naturally” occur. An open door at the end of the hall can affect the
ventilation of the fire, possibly pulling it away from the true area of origin
to more heavily damage the area near the ventilation source. Once ignited
by radiant heat or flame impingement, an unusually heavy fuel load in one part
of the room can cause greater damage than less loaded areas. The good
news is that these conditions can be observed at the scene and their effect
included in the fire flow analysis. But, the investigator must look for
them and actively analyze their potential effects, not blindly go by the adage
of “least to most, lowest part, there’s your area of origin.”
And then, there’s the
postflashover scene. When a fire proceeds through flashover and into the
full room involvement phase, the chaotic air flow and “firestorm”-like
conditions can alter, obscure, or obliterate the original fire patterns, as
well as cause unusual physical damage. The
full room involvement stage typically produces heat flux readings at floor
level of 170 kW/m2, which is sufficient to ignite most floor coverings and
construction materials, creating extensive areas of low burning that may or may
not be proximate to the area of origin. Full room involvement can burn
exposed wood on floors, window sills, and baseboards, even taking advantage of
small gaps in wall construction to draw in air that causes ventilation effects.
Some of these
potential postflashover effects mimic effects that can be caused by ignitable
liquids, such as curling of vinyl floor tile and spalling of concrete. Anytime a room reaches flashover, concrete
will spall. Unusual effects, like
charring of the undersides of furniture, burning of floor coverings under
furniture, burning under doors, and burning holes in floors have been observed
with full room involvement fires. The
myth that effects like burning under furniture can only be caused when an
accelerant is poured under the furniture does not hold true when everything in
the room is on fire. In a postflashover
fire, the turbulent mixing between combustion gases and fresh air being drawn
into the room causes high and variable heat fluxes that can cause irregular
damage to floors and floor coverings. They can also cause more intense burning
around ventilation openings and melt synthetic fabrics and carpets. In fact, in a post-flashover fire, the fire
becomes ventilation-controlled and the most intense fire, and therefore the
most intense thermal damage, may be near the air supply, such as open windows
or doors. Ventilation-controlled fires
can, near ventilation sources, produce the characteristic V-pattern that is
typically seen as an indication of fire origin. In a ventilation-controlled fire, if a
V-pattern is found near a door, for example, the investigator must consider whether
this might have been an effect of the postflashover burning, rather than an
area of origin. As these effects show, flashover makes the determination of the
first material ignited much more difficult, as heavy burning may now occur in
many places.
In summary, The key
in tracing fire flow and finding the area of origin is, in reality, far more
complex than the myth of most damage and lowest burning. The investigator
must observe and take into account all the physical properties of the
compartment, including ventilation, fuel load, configuration, the stage of the
fire (and whether or not flashover was achieved)—and the interaction between
all of these factors plus the unique characteristics of that environment.
Today,
fire scientists and investigators should have a better understanding of the
nuances of low burn and deep burn patterns, as well as the various factors that
create the appearance of separate multiple points of origin. Continuous, targeted education regarding these
indicators will ensure that investigators understand and effectively analyze
the extent to which patterns are attributable to accelerant and/or other
factors.
4.
Spalling
A
Fire Marshal report includes an assessment of spalling evidence as follows:
The examination
of the porch concrete floor disclosed an area of brown discoloration at the
base of the north wall and in front of the door to the central hallway. This
discoloration, or brown condition, is also an indication that a liquid accelerant
burned on the concrete.
Spalling
(i.e., brown discoloration or chipping or pitting of concrete or
masonry surfaces) occurs when concrete, masonry or brick is exposed to a high
rate of heating by flame or high levels of radiation from fuel. Spalling is characterized by the loss of
surface material resulting in cracking, breaking, and chipping or in the
formation of craters on concrete, masonry, rock, or brick. Fire-related spalling is the breakdown in
surface tensile strength of material caused by changes in temperature,
resulting in additional mechanical forces within the material.
Concrete spalling above a doorway caused by
fire
A mechanism of spalling is the expansion or
contraction of the surface while the rest of the mass expands or contracts at a
different rate; one example is the rapid cooling of a heated material by water.
Spalled areas may appear lighter in color than adjacent areas. This lightening can be caused by exposure of
clean subsurface material. Adjacent areas may also tend to be darkened by smoke
deposition. Another factor in the
spalling of concrete is the loading and stress in the material at the time of
the fire. Because these high-stress or high-load areas may not be related to
the fire location, spalling of concrete on the underside of ceilings or beams
may not be directly over the origin of the fire.
Controlled
laboratory experiments have shown that while spalling may be caused by burning
accelerant, it is more often caused by sustained heat from other sources. It is critical that today’s investigators
understand how to properly analyze spalling evidence. For example, investigators should identify
appropriate samples of adjacent materials and send those materials for
laboratory testing to determine whether accelerant is present.
The presence of spalling at a fire scene
cannot be taken as a definitive indicator that an accelerant was used in the
fire. Rather, the presence of the
spalling should be explained, if possible, and then treated as one of many
factors that enter into assessing the totality of the circumstances at the
scene and their relationship to determining the heat source and first material
ignited.
5.
Fire and Burn
Intensity
Pulled
bulb, showing that the heat was from the right
A
Fire Marshal Vasquez testified as follows regarding his interpretation of burn
intensity:
And aluminum melts at 1200 degrees
normal. Wood fire does not exceed 800 degrees. So to me, when aluminum melts,
it shows me that it has had a lot of intense heat. It reacts to it. That means
its temperature is hot. The temperature cannot react. Therefore, the only thing
that can cause that to react is an accelerant. You know, it makes the fire
hotter. It’s not normal fire.
So when I found that the floor is
hotter than the ceiling, that’s backwards, upside down. It shouldn’t be like
that. The only reason that the floor is hotter is because there was an
accelerant. That’s the difference. Man made it hotter or woman or whatever.
Human being made it hotter.
The fire, itself, tells me that it’s a
very aggressive fire; and, therefore, the fire was not a planned fire. It was a
spur-of-the-moment fire.
Wood
and gasoline burn at essentially the same flame temperature. In
the early 1990’s, the “widely held belief” among fire investigators was that
the flames of a wood-fueled fire are cooler than those fueled by petroleum products. Thus, investigators would often conclude that
a “hot fire” must have had an accelerant ignition. Scientists now know that flame temperatures
for normal fuels against liquid fuels are similar, and compartment temperatures
alone cannot be used to distinguish whether ordinary or liquid fuels were
involved. It is critical that today’s
fire investigators understand the significance of flame temperature and heat
release rates, and how these factors should be viewed within the context of
other indicators.
If
the investigator knows the approximate temperature required to produce an
effect, such as melting, color change, or deformation a material, an estimate
can be made of the temperature to which the material was raised. This knowledge may assist in evaluating the
intensity and duration of the heating, the extent of heat flow, or the relative
rates of heat release from fuels. When using materials such as glass, plastics, and white pot
metals for estimating temperature, the investigator is cautioned that there is
a wide variety of material properties for these generic materials. The best method for utilizing such materials
as temperature indicators is to take a sample of the material and have its
properties ascertained by a competent laboratory, materials scientist, or
metallurgist.
In
addition to the wood and gasoline burning at essentially the same flame
temperature, the turbulent diffusion flame temperatures of all hydrocarbon
fuels (plastics and ignitable liquids) and cellulosic fuels are approximately
the same, although the fuels release heat at different rates. Burning metals
and highly exothermic chemical reactions can produce temperatures significantly
higher than those created by hydrocarbon- or cellulosic-fueled fires.
In summary, fire patterns are generated by one of two
mechanisms: the spread of the fire or the intensity of burning. As discussed above, fuel composition, rate of
heat release, location, and ventilation differences may lead to differences in
the intensity patterns that do not necessarily point to the area where the
first fuel was ignited. Patterns that
arise from the growth and movement (spread) of the fire are invariably better indicators
of the area of origin. It may be
difficult, however, to distinguish movement patterns from intensity patterns. Further, some patterns display a combination
of intensity and movement (spread)
indicators.
•
Holes in the floor may be caused by glowing
combustion, radiation or an ignitable liquid.
•
There is no justification that the appearance of
large, curved blisters is an exclusive indicator of an accelerated fire.
•
The presence or absence of spalling should not, in
and of itself, be construed as an indicator of the presence or absence of a
liquid fuel accelerant.
•
Inverted cone patterns have been interpreted as
proof of flammable liquid fires, but any fuel source that produced flame zones
that do not become vertically restricted can produce inverted cone patterns.
6.
Crazed
Glass
Crazing of glass in a fire where no
accelerants were used
Crazing
is a term used in the fire investigation community to describe a complicated
pattern of short cracks in glass. A Fire
Marshal made the following statement regarding crazed glass in his report in an
arson case:
The pieces of broken window glass on
the ledge of the north windows to the northeast bedroom disclosed a crazed
‘spider webbing’ condition. This condition is an indication that the fire
burned fast and hot.
Crazing
is the result of the rapid cooling of glass in a hot environment by the
application of water spray. Fire scientists
and investigators have concluded that it no longer has any value as an indicator. Today’s investigators should not mention the
presence of crazed glass in a fire scene report. If crazed glass were mentioned, corrective
action would be taken immediately.
Incendiary
indicators, including but not limited to those discussed above, are subject to
numerous variables that require continuous study and evaluation. Scientific understanding of the indicators has
continued to advance as additional experiments are conducted. Training must ensure
that fire investigators clearly understand all incendiary indicators and their limitations,
including the possible effects of phenomena such as flashover and associated
radiation, ventilation, smoldering debris and drop-down effects. Whatever training is provided must include an
environment in which investigators and scientists are free to exchange
information and engage in honest and open dialogue regarding fire behavior and
incendiary indicators.
Confirmation of Accelerant Through Laboratory Testing
In
one arson case, ten samples were sent for testing. None of the samples tested
positive for accelerant. In another case,
an unspecified number of samples were sent for testing, and one (under the aluminum
threshold of the front door) tested positive for accelerant.
At
the time these cases occurred, positive laboratory results were accepted if
they were available, but they were not considered necessary to reach the conclusion
that the fire involved intentional use of an accelerant.
As
technology advanced, fire scientists and investigators developed a better understanding
of the importance of confirmatory testing. Experts have also noted that
technology used in gas chromatography/mass spectrometry and other laboratory testing
is more sensitive today than it was in the early 1990’s. As a result,
laboratory tests are better able to detect evidence of accelerant than they were
two decades ago. Due to the passage of time, re-testing of samples taken in the
Willis and Willingham cases is not an option.
The
Five Most Common Arson Myths
1.
The lowest and
deepest charring indicates the point of origin in a fully involved room.
2. In a fully involved
room, an experienced investigator can identify patterns produced by ignitable
liquids on the basis of visual observation alone.
When
a fire breaks out, a phenomenon called flashover can occur. Flashover is a
transition point at which heat causes almost everything in a room to catch
fire. When it happens, the natural patterns of the fire can be obscured or
destroyed. V-shaped burn patterns, which often occur after a flashover, can be
misinterpreted to indicate arson.
3. Flammable liquids
burn at a higher temperature than ordinary combustibles.
It's a common
misconception that gasoline burns at a higher temperature than wood. It's
actually the amount of ventilation that determines the temperature of the fire,
not the nature of the fuel.
4. Spalling or flaking
of concrete, especially in a "puddle" shape, is an indicator of the
presence of burning ignitable liquids.
Fire
tests have shown that "puddle" shapes can occur after a flashover.
5. Heat rises and fire
always
burns upward. Floor
level burning is therefore an indication of an incendiary fire.
The
idea that a fire will not burn downward unless it has "help" is a
simplistic explanation of fire behavior that doesn't take into account the
flashover phenomenon. It was widely believed that burning on the floor,
particularly under furniture, indicated an origin on the floor, and pointed
toward arson.
Additional
Myths Still in Favor in Some Quarters Today
6. Multiple low burns,
or multiple V-shaped burn patterns, even if they are burned together, indicate
multiple origins.
7. Using models, it is
possible to calculate fire behavior precisely.
8. A narrow V-pattern
indicates a rapidly burning fire, whereas a wide V-pattern indicates a
"normal" fire.
9. Although flashover
and full room involvement can generate ambiguous patterns, flashover is rare.
(Flashover is a transition point at which you go from having a fire in a room
to a room on fire).
10.
A melted aluminum threshold is unusual in a
"normal" fire, and tends to indicate the presence of ignitable
liquids.
Myths
That Have Been Largely Discredited, And Are Only Used By Those Profoundly
Unaware Of The Science
1. "Crazed"
glass, broken throughout, indicates that the glass was rapidly heated. Further,
the size of the crazing can provide information about the origin.
2. The size and
appearance of char blisters can provide information about what was burning, and
how rapidly it was burning.
3. An unconfirmed
canine alert constitutes valid evidence of an accelerant.
4. The temperature of
a fire follows a "standard time-temperature curve."
5. The heat release
rate of a fire can be predicted by knowing the weight of combustible fuels in a
room.
Metropolitan Engineering, Consulting &
Forensics (MECF)
Providing Competent, Expert and Objective Investigative Engineering and
Consulting Services
P.O. Box 520
Tenafly, NJ 07670-0520
Tel.: (973) 897-8162
Fax: (973) 810-0440
E-mail: metroforensics@gmail.com
http://metroforensics.blogspot.com/
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account. Please make sure to follow us at @MetropForensics or
@metroforensics1
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Feel free to recommend our services to your friends and colleagues.