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Lecture Arson Analysis of Fire Debris. Arson is defined as purposely setting fire to a house, building or other property . . Rules of a Fire’s Origin. 1997 Arson Statistics. The fire burns up and out (v-pattern). The presence of a combustible material is needed.

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lecture arson analysis of fire debris

Lecture ArsonAnalysis of Fire Debris

Arson is defined as purposely setting fire to a house, building or other property.

1997 arson statistics

Rules of a Fire’s Origin

1997 Arson Statistics

The fire burns up and out (v-pattern).

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.

  • Arson is the second leading cause of death by fire in the U.S. An estimated 500 Americans died in arson-related 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).
arson investigation
Arson Investigation
  • Ignition temperature.
    • Combustion will continue until:
      • 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.
arson investigation5

Ignition temperature and flash points are NOT related!

Arson Investigation
  • Definitions.
    • Flammable liquid.
    • Combustible liquid.
    • Flammable.
    • Flammable or explosive limits.
    • Vapor density.

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


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.

arson investigation7
Arson Investigation
  • 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.
  • 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).

arson investigation9
Arson Investigation
  • 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 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.





Lighter fluids

Charcoal starters

Automobile additives

Camping fuels

classification of accelerants
Classification of Accelerants

1. Light petroleum distillates (LPD)

2. Gasoline

3. Medium petroleum distillates (MPD)

4. Kerosene

5. Heavy petroleum distillates (HPD)

6. Miscellaneous

light petroleum distillates 1

Gasoline (2)

Light petroleum distillates (1)

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.

  • 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.
medium petroleum distillates 3

Kerosene (4)

Medium Petroleum Distillates (3)

Produced by distilling crude oil.

Made from the C9 through C16 range of hydrocarbons.

Class representatives: kerosene, jet fuel, and lamp oils.

  • 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.
heavy petroleum distillates 5

Miscellaneous (6)

Heavy Petroleum Distillates (5)

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.

  • Produced by distilling crude oil.
  • Made from the C10 through C23 range of hydrocarbons.
  • Class representatives: diesel, lamp oils and home heating oils.
evidence of accelerants
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

Steps to Recover and Identify Accelerants
  • The evidence container should have the following qualities:
    • Air tight
    • Highly resistant to breakage
    • Prevents cross-contamination
    • Good integrity seal
  • Collect samples.
  • Extract the fire debris and obtain a sample for instrumental analysis.
  • Carry out instrumental analysis.
  • Interpret the results.
collection of evidence

Common Sampling Errors

Collection of Evidence

Insufficient sample

Taking samples from the wrong places or materials

Ineffective sample preservation techniques

No comparison samples

Not maintaining an evidence “chain of custody”

  • 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.
accelerant identification
Accelerant Identification
  • Identification consists of three steps:
    • Sample preparation
    • Instrumental analysis
    • Data analysis
  • 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.

A gas chromatograph is coupled to a mass selective detector.

  • 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.
an ignitable liquid is detected

No Ignitable Liquids Were Detected

An Ignitable Liquid Is 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.

  • “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.”