Arson

1
Arson
2
Whats Arson?

• Arson is defined as purposely setting fire to a
  house, building or other property.
• Legal Question Did someone purposefully set the
  fire, and if so who?
• Since most materials dont easily ignite, an
  arsonist will often employ an ignitable fluid to
  start the fire
• Presence of an ignitable fluid does not, in and
  of itself, establish the legal crime of arson

3
Arson Statistics (2001)

• Arson is the second leading cause of death by
  fire in the U.S. An estimated 475 Americans died
  in arson-related fires and 2,000 were injured.
• 50 of arson fires occur outdoors, 30 in
  structures and 20 in vehicles.
• 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).

4
The Fire Triangle

• Fire requires fuel (carbon), heat and oxygen the
  fire triangle.
• If any one component is missing, a fire will not
  start or it will be extinguished.
• Water helps put out a fire by removing heat and
  the steam produced pushes oxygen away.

5
The Heart of a Fire Combustion

• A reaction in which a hydrocarbon reacts with
  oxygen and produces carbon dioxide and water.
• Also called oxidation-reduction or redox since
  oxidation and reduction always occur together.
• Examples
• CH4 2 O2 ----gt CO2 2 H2O (addition/loss of O
  or H)
• 4 Fe 3 O2 ---gt 2 Fe2O3 (addition/loss of e-
  rusting)
• 4 C3H5N3O9 --gt 12 CO2 10 H2O 6 N2 O2

6
Chemical Reactions What Makes Them Happen?

• Potential energy is stored in the chemical bonds
  and energy is required to break them.
• A reactions driving force is its ability to
  rearrange the bond to give a lower energy.
• The net energy from breaking old bonds and making
  new ones bonds is either released or absorbed
  when a reaction occurs.
• Exothermic reactions net energy release.
• Endothermic reactions net energy loss.

7
Arson
8
Reaction Energy Diagrams
9
Chemical Reactions What Starts Them?

• Heat is needed to convert the fuel to vapor and
  to get reactants to collide with enough force.
• To initiate a reaction, colliding molecules must
  have enough energy to break bonds.
• This energy required to initiate a reaction is
  called the activation energy.
• The energy required to overcome the activation
  energy comes from molecular collisions.
• Increasing the heat increases the number and
  force of molecular collisions.

10
Chemical Reactions What Keeps Them Going?

• When new bonds in the products form, energy is
  released.
• If more energy is produced making bonds in the
  products than was used in breaking them in the
  reactants, then there is a net surplus of energy.
• This energy surplus is used to make the remaining
  reactants collide faster and with more force so
  even more overcome the activation energy.
• When no more reactants are left, the reaction
  stops.

11
Fire Event Sequence
Taken in part from a seminar by Jim Kahoe and
Greg Brown
12
Sequence of Events During a Fire

• Incipient stage
• Stage begins with ignition of fire
• Hot gases rise in the room
• Oxygen dives to the bottom of the flames
• Free-burning stage
• Fire consumes more fuel and intensifies
• Flames spread upward and outward
• Dense layer of smoke and gases accumulate near
  ceiling
• Smoldering stage
• All fuel or oxygen is consumed and the fires
  open flames disappear
• If oxygen suddenly enters the area, the hot soot
  and fire gases can ignite with explosive force,
  or backdraft.

13
Starting a Fire

• Molecules of fuel must be in gaseous state to
  produce a flame. Liquids and solids must be
  heated to form gases.
• Molecules of fuel must be mixed with a sufficient
  quantity of air (oxygen).
• An ignition source supplies the initial
  activation energy and starts the reaction
• Ignition sources are usually chemical, mechanical
  or electrical (match, flint steel, static
  spark, etc.)

14
Starting a Fire

• Ignition temperature is when the heat produced
  can create a self sustained reaction.
• Flash point the minimum temperature at which a
  liquid fuel will produce enough vapor to burn
• Flammable liquids flash points lt 100 F
• Combustible liquids flash points 100 F
• Once a liquid reaches its flash point, fuel can
  be ignited by an outside source of heat
• Ignition temperature gt flash point (Table 10-1)

15
Keeping A Fire in Balance

• As fire burns, it raises the temperature of the
  fuelair mixture and creates more fuel vapors,
  which increases the rate of reaction. For every
  increase of 10C or 18F, the burn rate doubles.
• Flammable range the range of concentrations of
  gaseous fuel that will support combustion.
• Lower explosive limit lowest concentration that
  will burn. The LEL of gasoline is 1.3.
• Upper explosive limit highest concentration that
  will burn. The LEL of gasoline is 6.

16
Fueling a Fire

• Wood, plastic or other hydrocarbon materials will
  burn when heated to a temperature that is hot
  enough to decompose the solid and produce
  combustible gaseous products.
• Fats are slowly rendered to grease and oils that
  produce flammable vapors.
• Liquid accelerants form flammable or explosive
  vapors even at room temperature.

17
Accelerants
18
Accelerants

• Accelerants are any liquid, solid or gaseous
  material that will sustain or enhance
  flammability.
• Solid and gas accelerants Group 1 2 metals,
  black powder, natural gas, spray can propellants,
  etc.
• Liquid accelerants are commonly used because of
  ease of ignition and familiarity of use.
• Liquid accelerants are usually mixtures of
  alkanes and aromatic hydrocarbons.

19
Classification of Ignitable Liquids
20
Properties of Ignitable Liquids

• Behave like any liquid before ignition
• Float on water (can create a rainbow sheen)
• Dont dissolve
• Often form vapors at room temperatures that are
  heavier than air
• Powerful solvents of other hydrocarbons readily
  absorbed by organic matter
• Dont spontaneously ignite

21
Properties of Ignitable Liquids
Flash point - The temperature at which a
flammable liquid gives off enough vapors to
ignite. The ignition temperature - the
temperature required for a liquid to reach its
activation energy.
From Table 10-1
Ignition temperature and flash points are NOT
directly related!
22
Properties of Ignitable Liquids
23
Fire Investigations
24
Fire Investigation Basics

• Work from the least damaged areas to the most
  heavily damaged areas.
• Document with notes, photographs, and videos.
• Collect evidence (accelerant samples, fire items,
  and other crime scene evidence.)
• Interview witnesses
• Determine the point of origin.
• Try to recreate events just before and after the
  start of the fire.

25
Questions to Be Asked

• What was the heat source?
• What was the fuel?
• What provided the oxygen supply?
• Evidence of an ignition device?
• Evidence of a accelerant or ignitable fluid?
• Accident or arson?

26
Accident or Arson?

• Accident
• Heating System malfunction
• Electrical appliance malfunction
• Lightning
• Children playing with matches
• Smoking
• Arson
• Odor or smoke from accelerants
• Locked windows, blocked doors
• Ignition devices
• Two or more points of origin
• Inverted V-pattern or hourglass burn pattern
• Pour patterns or trailers that lead the fire from
  one place to another

27
Examination of a Fire Scene

• Work backward in relation to fire travel and from
  least to most damage.
• Photograph and document the condition of doors,
  windows, and locks.
• Look for unusual burn patterns.
• Point of origin gives a starting point for
  evidence collection.
• Look for accelerant residues at the edges of burn
  patterns.

28
Point of Origin Fire Patterns
29
Point of Origin (POO)

• Defined as where the fire originated.
• Fires tends to go up and/or follow ventilation or
  fuel paths and the POO will be near the most
  burned area.
• Sometimes multiple patterns will appear due to
  burning debris which may fall in the path of the
  fire
• If accelerants or ignition devices were used,
  they may be present.
• Dig out samples for analysis since the accelerant
  may have been absorbed by the ground material.

30
Fire Patterns
(C)
(A)
(B)
(E)
(F)
(D)
31
Fire Patterns in Evidence
32
Fire Patterns as Evidence
33
Fire Patterns as Evidence
34
Finding Accelerants

• Accelerants are found where there are
• Large amounts of damage
• Unusual burn patterns
• High heat stress on metals
• Multiple sites of origin
• To find the best place to collect samples use
• Your nose or better, a dogs!
• Rainbow sheen in water
• Portable detectors or sniffers (detects change
  in oxygen level on a semiconductor)

Dogs can detect 0.01 mL of 50 evaporated
gasoline 100 of the time.
35
Collecting Arson Evidence
(Plastic bags must be nylon)

• Do NOT use
• plastic containers (may react with evidence)
• paper bags (might soak up evidence)

36
Collecting Arson Evidence

• Ignitable fluids are volatile so used tightly
  sealed containers that also wont soak up
  hydrocarbons.
• Collect a large quantity of ash soot for
  suspected point of origin since it may contain
  remnants of unburned or partially burned
  ignitable fluid.
• Suspects clothing may also contain fluid
  residue.
• Collect substrate samples of materials similar to
  those from point of origin but far enough away to
  allow a clear comparison.

37
Sample Preparation Headspace Analysis

• Material collected in an airtight can is gently
  warmed inducing a vapor which rises to occupy the
  empty top space.
• A sampling device such as a syringe is used to
  puncture the can and collect a sample of the
  headspace.

38
Sample Preparation Solid-phase Microextraction

• Hydrocarbon vapors are collected concentrated
  on an adsorptive strip of charcoal-coated teflon.
• A strip is sealed in a container with the
  evidence and warmed to release vapors which are
  adsorbed by the charcoal.
• The strip is washed with a small quantity of
  solvent to remove the sample for analysis.

39
Sample Preparation Direct Solvent Extraction

• Pentane or other solvent is added to evidence
  sample
• Pour off solvent
• Allows you to concentrate the sample
• Not the best method since it destroys the sample.

40
Debris and Accelerant Analysis
41
Analysis of Fire Scene Evidence

• GC (Gas Chromatography) and GC-MS (Mass
  Spectrometry) are the most commonly used
  techniques. GC is inexpensive, MS is expensive.
• IR (Infrared Spectroscopy) can analyze for
  different functional groups but will not easily
  discriminate between different alkanes or
  mixtures. More expensive than GC but cheaper to
  maintain.
• HPLC (High Performance Liquid Chromatogrpahy) Not
  suitable for gas samples. It can be used to
  separate heat sensitive mixtures not suitable for
  GC (explosives). More expensive than GC.

42
What Information Can Be Obtained from GC?

• The number of components in a mixture.
• The relative polarity or molar mass of the
  components.
• Common origin of evidence reference sample. For
  example, a sample from the scene and from a gas
  can in suspects car.
• Becomes more difficult if volatiles evaporated or
  are burned away.

43
GC of Gasoline

• Gas chromatograph of vapor from debris recovered
  at a fire site. (top)
• Gas chromatograph of vapor from a genuine
  gasoline sample. (bottom)
• Note the similarity of the known gasoline to
  vapor removed from the debris.

44
Identification of Accelerants
You can classify the substance by the pattern of
peaks, for example gasoline vs. kerosene
unevaporated gasoline
90 evaporated gasoline
unevaporated kerosene
90 evaporated kerosene
45
Gas Chromatography

• Used to separate mixtures of volatile organic
  compounds
• Distributes components of a mixture between an
  gaseous mobile phase and a solid stationary phase
  to separate them.
• Each component exits the instrument at a
  different time, depending on its interaction with
  these two phases and is detected.
• Components produce peaks where the area under
  each peak is proportional to the amount.

46
Schematic of a GC
The sample is separated in the column, and the
carrier gas and separated components emerge from
the column and enter the detector (5). Signals
developed by the detector activate the recorder
(7), which makes a permanent record of the
separation by tracing a series of peaks on the
chromatograph (8). The time of elution identifies
the component present, and the peak area
identifies the concentration. Courtesy Varian
Inc., Palo Alto, Calif.
47
Gas Chromatography (GC)

• Volatile materials are heated to high
  temperatures so that they will become a gas and
  flow through the GC column.
• They are carried by a mobile phase, usually
  helium or nitrogen .
• The stationary phase is a thin film of liquid.
  Usually a type of silicone polymer coated to the
  wall or on a support material.
• After a mixture has traversed the length of the
  column, it will emerge separated into its
  components.

48
The Basics of Chromatography

• Different compounds will stick to a solid surface
  with different degrees of strength.
• This stickiness is determined by the magnitude
  of the intermolecular forces between the sample
  and the stationary phase.
• When a mixture of compounds flows over a surface,
  the molecules will stick unstick many times as
  they are swept along.
• Over time, the molecules with different amounts
  of stickiness will become physically separated
  from each other.

49
The Basics of Chromatography
50
The Basics of Chromatography
51
The Basics of Chromatography
52
The Basics of Chromatography
53
The Basics of Chromatography

• When the components reach the far end of the
  stationary phase, they are detected or measured.
• Chromatography is non-destructive and does not
  alter the molecular structure of the compounds it
  separates.
• The components could be collected and/or their
  amounts measured.
• The time required for each component to escape
  the apparatus can be measured.

54
GC Retention Time
55
GC Data Analysis

• The time required for a component to emerge from
  a GC column is known as retention time.
• Retention time can be used as an identifying
  characteristic of a substance
• retention times may not be unique
• GC is not an absolute method of identification
• An extremely sensitive technique
• area under a peak is proportional to the quantity
  of substance present
• allows quantitation of sample

56
Problems with GC Analysis

• The GC gives only relative amounts, polarity or
  molar mass. It cannot easily identify compounds.
• To overcome this problem
• a reference liquid may be run for comparison or
  mixed with the sample to see which peaks are
  enhanced
• the GC may be attached to a mass spectrometer
• Mass spectrum indicates the exact molar mass of
  each component.

57
GC-MS Analysis

• A sample is automatically injected on the gas
  chromatograph / mass spectrometer (GC/MS).
• The GC will separate all of the samples
  components.
• The MS will identify the samples components from
  their unique mass patterns.

58
If No Accelerants are 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.