Transcript Arson Investigation - St. Edward's University

Lecture Arson
Analysis of Fire Debris
Arson is defined as
purposely setting fire to
a house, building or
other property.
1997 Arson
Statistics
Arson is the second leading
cause of death by fire in the
U.S. An estimated 500
Americans died in arsonrelated fires.
Arson caused more than $2
billion in property damage.
Only 19% of arson cases
resulted in arrest, and only 2%
were convicted.
50% of arsonists are under the
age of 20 (40% are under 15
years old).
Rules of a Fire’s
Origin
The fire burns up and out (vpattern).
The presence of a combustible
material is needed.
The fire needs fuel and oxygen
to continue.
The fire’s spread will be
influenced by air currents, walls
and stairways.
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Ignition temperature.
Combustion will continue until:
1.
2.
3.
4.
Fuels are consumed.
Oxidizing agent has been removed.
Fuels are cooled below their ignition temperature.
Flames are chemically retarded.
Transfer of heat. :
Conduction.
Convection.
Radiation.
Direct flame contact.
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Definitions.
Flammable liquid.
Combustible liquid.
Ignition temperature and flash
points are NOT related!
•Liquid
•Flash
Point
Flammable or
explosive limits.
•Gasoline
-45oF
536oF to
853oF
Vapor density.
•Kerosene
100oF
410oF
Flammable.
•Ignition
Temp
Flash point - The temperature at which a particular flammable liquid
gives off vapors (vaporizes) and therefore can ignite.
The ignition temperature is the temperature required for a liquid to
continue to emit vapors that can sustain
combustion.
A flammable liquid in its liquid state will not burn. It only will
ignite when it vaporizes into a gaseous state. All flammable liquids
give off vapors that can ignite and burn when an ignition source such as
a lighted cigarette or spark is present.
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Point of Origin (POO).
Defined as where the fire originated.
Cause of fire may be near the POO.
Fire usually burns longer at POO.
If accelerants or ignition devices
used, they may be present at the
POO.
Multiple POO’s MAY indicate arson.
“V” patterns usually point to the
POO.
Extensive ceiling damages may be
present above the POO.
Point of Origin (POO).
Interior Examination.
Work backward in relation to
fire travel and from least to most
damage.
Ceiling damage may lead to
POO.
In accidental fires, floor damage
is limited in respect to the
ceiling damage.
“V” patterns may help locate
POO.
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Metal
Solder
Tin
Lead
Zinc
Magnesium
Aluminum
Silver
Gold
Copper
Iron
Chromium
Melting Temperature, oF
361
449
618
878
1202
1220
1761
1945
1981
2781
3497
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Investigation of Vehicle Fires.
Vehicular fires are investigated just as structural
fires.
Accidental fires tend to be isolated to one area of
the vehicle.
Incendiary fires tend to consume the entire
vehicle and are very hot.
The loss of temper of the seat strings may be
observed.
Accelerants
Accelerants are any liquid, solid or
gaseous material that will sustain or
enhance flammability.
Liquid materials are commonly used
because of ease of ignition and
familiarity of use.
Accelerants are nearly exclusively
derived from hydrocarbons.
Straight chain hydrocarbons are the
backbone of the oil industry.
Hydrocarbons are molecules made up of
the elements hydrogen and carbon.
Octane is a term familiar to all. It
consists of a hydrocarbon having 8
carbons.
Examples:
Gasoline
Kerosene
Diesel
Lighter fluids
Charcoal starters
Automobile additives
Camping fuels
Classification of
Accelerants
1.
2.
3.
4.
5.
6.
Light petroleum distillates (LPD)
Gasoline
Medium petroleum distillates (MPD)
Kerosene
Heavy petroleum distillates (HPD)
Miscellaneous
Light petroleum
distillates (1)
Produced by distilling
crude oil.
Made from the C4
through C11 range of
hydrocarbons.
Class representatives:
petroleum ether, cigarette
lighter fluid, some
camping fuels and
solvents.
Gasoline (2)
A refined petroleum
mixture of the C4 through
C12 range.
Produced from crude oil
using the ‘cracking and
reforming’ production
method.
All brands and grades of
automotive gasoline fit
within this category.
Medium Petroleum
Distillates (3)
Produced by distilling
crude oil.
Made from the C8
through C12 range of
hydrocarbons.
Class representatives:
paint thinners, mineral
spirits, dry cleaning
solvents and charcoal
starter containing mineral
spirits.
Kerosene (4)
Produced by distilling crude
oil.
Made from the C9 through C16
range of hydrocarbons.
Class representatives:
kerosene, jet fuel, and lamp
oils.
Heavy Petroleum
Distillates (5)
Produced by distilling
crude oil.
Made from the C10
through C23 range of
hydrocarbons.
Class representatives:
diesel, lamp oils and
home heating oils.
Miscellaneous (6)
Produced by collecting and
recombining certain fractions
of distilled crude oil.
Made from a wide range of
hydrocarbons.
Class representatives: brush
cleaners, thinning agents,
strippers, products for home,
automotive and industrial use.
Evidence of Accelerants
Large amounts of damage
Unusual burn patterns
High heat stress
Multiple sites of origin
“Sniffers”
Portable gas chromatographs
Chemical tests
Canines
Portable detectors
Detect change in oxygen level on a
semiconductor
Guides to the best place to collect
samples
Dogs can detect 0.01 mL of
50% evaporated gasoline
100% of the time.
0.01 mL is about the size of
a thousandth of a drop.
Steps to Recover
and Identify
Accelerants
Evidence
Containers
Collect samples.
Extract the fire debris
and obtain a sample
for instrumental
analysis.
Carry out instrumental
analysis.
Interpret the results.
The evidence container
should have the following
qualities:
Air tight
Highly resistant to
breakage
Prevents crosscontamination
Good integrity seal
Collection of
Evidence
Begin the search by looking
for objects that do not seem
to belong.
Concentrate the search
beginning where the
suspected accelerant
container was found.
Store the samples in
containers where they will
not be contaminated.
Common
Sampling Errors
Insufficient sample
Taking samples from the wrong
places or materials
Ineffective sample preservation
techniques
No comparison samples
Not maintaining an evidence “chain
of custody”
Accelerant
Identification
Identification consists of three steps:
Sample preparation
Instrumental analysis
Data analysis
Extraction
Common methods used today:
Steam distillation
Vacuum distillation
Solvent extraction
Charcoal sampling
Swept headspace .
The can containing the debris is first identified by a unique case and item
number
A hole is punched in the lid.
A rubber plug containing two carbon sampling strips are inserted into the
can.
The can with the sampling strips is put into the oven and heated.
After heating, the carbon strips are put in separate glass vials.
One strip is sealed dry and is stored for re-testing purposes, if necessary .
The other is placed in carbon disulfide, a solvent.
Analysis
The vial is automatically
injected on the gas
chromatograph / mass
selective detector
(GC/MSD).
The GC will separate all
of the sample’s
components.
The MSD will identify
the sample’s components.
A gas chromatograph
is coupled to a mass
selective detector.
An Ignitable Liquid
Is Detected
“Sample contains a medium
petroleum distillate (MPD),
some examples are paint
thinners and mineral spirits”.
“Sample contains a mixture of
gasoline and a heavy petroleum
distillate (HPD). Some
examples of a HPD are diesel
fuels and heating oils.”
No Ignitable
Liquids Were
Detected
We can look at this in four different
ways...
No ignitable liquids were ever used
Ignitable liquids were used to start the
fire, but have been totally consumed.
Ignitable liquids are still present;
however, not in the collected sample.
Ignitable liquids are still present in the
collected sample; however, they are
too dilute to be detected.