ARSON = purposely setting fire to a house, building or other property.

•Arson is the second leading cause of death by fire.

•Estimated 500 Americans die in arson-related fires each year

•Arson causes more than $2 billion in property damage each year.

•Only 19% of arson cases resulted

in arrest; Only 2% were convicted.

U.S. Arson Stats

Cause of fire • Natural • Accidental• Incendiary (intentional).• Suspicious

• Unknown

The Chemistry of fire

While there are millions of different chemical reactions, chemists tend to group them into three main types:

precipitationacid-baseoxidation-reduction*

Fire is an example of an oxidation-reduction reaction (sometime called a combustion reaction).In an oxidation-reduction reaction there is a transfer of electrons from one chemical… (the reducing agent) to another chemical… (the oxidizing agent).

The reducing agent is simply the fuel.The oxidizing agent in most fires is

oxygen.

The Chemistry of fire

OxidationThe combination of oxygen with other substances to produce new substances

Example: CH4 + 2O2 CO2 + 2H2O

The Chemistry of fire

The Chemistry of fire

Pop quiz:Which is the oxidizing agent and which is the reducing agent?

The Chemistry of fire

The Chemistry of fire

BASIC DEFINITIONSIgnition temperature =Temperature at

which a fuel will spontaneously ignite.

Flashpoint =Temperature at which a liquid fuel will produce enough vapor to burn.

Flashover =Auto Ignition from super heating.

Backdraft = Oxygen is missing…vacuum created

The Chemistry of fireBASIC DEFINITIONS

Pyrolysis = a decomposition reaction that produces small gaseous compounds to combust. All flame fires are burning vapors or gasses

Glowing combustion = smoldering: on the surface of a solid fuel like cigarette or wood

Activation energy = E required to start reaction

Exothermic = means to give off heat

The three things needed to keep a fire going are FUEL, OXIDIZER, and HEAT. This is often called a fire triangle. If you remove any side of the triangle, the fire will go out.

The Chemistry of fire

Oxygen Heat

O2

Fuel

The Chemistry of fire

Can you now explain FIRE EXTINGUISH

Can you now explain FIRE RETARDANT

The Chemistry of fire

An arson investigator, even among the ruins, seeks to answer 2

questions:1-Where was the fire’s point of origin?

and

2-What was the cause of the fire?

The arson investigator uses physical and chemical evidence to seek

these answers.

The investigation of the fire scene

Investigators may use witnesses’ reports to help:

• Locate the point of origin

• Determine whether the fire was accidental or incendiary

• Figure out whether the arsonist used an accelerant

The investigation of the fire scene

Fire behaviorFires typically spread sideways and up from the point of origin; a ‘V’ pattern where the bottom of the ‘V’ points to the origin.

It happens in a perfect scenario where there are no drafts, corners, stairwells, synthetic carpets, etc….these cause unusual burn patterns. The most damage is by the point of origin.

V

The investigation of the fire scene

Multiple points of origin

This happens when an arsonist has started multiple fires within a building by either placing pools of accelerants in various locations or sloshes a path of accelerants.

The investigation of the fire scene

Stored fuels and other flammable liquids can interfere with the true point of origin.

The investigation of the fire scene

IntensityMaterials melt or buckle at certain temperatures. A fire engineer would know that glass melts around 1,500ºF and that steel beams buckle wherever the most intense fire is located

The investigation of the fire scene

Spalling The crackling and flaking on the walls and floors in areas of high heat

Wooden structures will look charred and flakey. Kind of what looks like black alligator skin… Have you seen a burned

log?

The investigation of the fire scene

TimingHaving a series of smoke detector helps. The alarms go off in sequence. This indicates the path of the fire.

The investigation of the fire scene

The investigation of the fire scene

SniffersVTA – A Vapor Trace Analyzer

Is a portable gas chromatograph. Presumptive test for accelerants.

K9 – 100% accuracy=Presumptive?

The best sniffers…

Dogsdetect 0.01

microliter of 50% evaporated

gasoline 100% of the time.

0.01 microliter is about the size of a thousandth

of a drop.

The investigation of the fire scene

Evidence CollectionMost accelerants are some sort of petroleum-based hydrocarbon such as gasoline or kerosene.

Evidence must be placed in a metal container so no fumes diffuse through the container.

Many linoleum flooring, carpet and tile adhesives have hydrocarbons in

them.

Control samples need to be collected

Evidence Collection

Confirmatory Tests• Headspace vapor extraction: The

vapor collected in the space above the material in a closed container is called the headspace. Heating the container really quickens the process. The vapor is removed with a syringe and analyzed for hydrocarbons via GC-MS

• Solvent Extraction: Material is dissolved in a solvent. The hydrocarbons are separated out then analyzed via GC-MS

Confirmatory Tests• Steam Distillation: Charred material is

heated, the steam is collected, condensed and analyzed for hydrocarbons via GC-MS

• Vapor concentration: A sample is heated in a closed container with charcoal inside to absorb the vapors. The charcoal is removed, hydrocarbons are extracted and analyzed via GC-MS

Arson Motives1. Concealment of a crime (theft,

murder…)2. Insurance Fraud/Profit3. Psychological reasons/Excitement4. Revenge5. Vandalism6. Terrorism/Extremist

remember the NOVA video?

Fun Fact…A person who thinks that they can cover up a murder with arson probably did not pass chemistry. Structural fires do not burn hot enough and long enough for a body to be completely destroyed. When a body is cremated, it needs to be exposed to temps around 1,500ºF for 2 or more hours. A structural fire can range from 500 - 2000ºF but not for the amount of hours needed; simply not enough fuel. Its amazing how much a significantly burned body can be well preserved internally. The ME can even search for signs of trauma and poisons.

Investigating Homicidal Fires

Whenever a body turns up at a scene, the M.E. must determine the cause of death. At a fire scene the M.E. must answer the question:

Was the victim alive at the time the fire started?

• What position was the body in? (See next slide.) Are there items of significance around them?

• What was the CO (carbon monoxide) levels in the blood and tissue? CO enters the blood and tissues when inhaled from the smoke. A normal level of CO in the blood is ≤ 5%. In victims of asphyxiation (suffocation) the level ranges from about 45 – 90. Also, too much CO in the lungs make you disoriented, unable to think or to move properly… and unable to escape.

• Was there soot in the lungs? Soot enters the lungs when smoke is inhaled.

Many people believe that a body found curled up shows that the victim was alive the time the fire reached them and that they died a painful death. This isn’t the case. A burning corpse assumes a boxer’s posture called a pugilistic position….arms and legs flexed and fists tucked under the chin. Actually this happens because the muscles are dehydrating rapidly causing them to contract.

Profile of the ArsonistYWM

AGE: majority under 18 (51%) if adult, late 20s, almost never over 35

SEX: 9 out of 10 times (90%) a male

RACE: 3 out of 4 times (75%) a white; black (20%)

CLASS: majority from lower to working class

FAMILY: absent or abusive father, history of

emotional problems with family/mother

SCHOOL: learning problems and usually held back

Profile of the ArsonistPEERS: social misfit, interpersonal problems with opposite sex, appears physically and emotionally

weak compared to peersWORK: usually chooses subservient position and

then resents it. CRIMINAL HISTORY: numerous offenses as

juvenile, almost all have arrest recordsARREST: majority remain at crime scene; some

attempt suicide in lockup; most will easily confess