Forensics Arson/Fire Investigation

What is Arson?

When a person sets something on fire on purpose. Can be to destroy property, hide a crime, or just because they like fire.

What makes arson investigations difficult?

1) The perpetrator thoroughly planned the act

2) The perpetrator is not present when the fire starts

3) Fire is extremely destructive → must work backwards to find the cause.

What questions must you find in an arson investigation?

1) How did the fire start? (what caused it? - igniter mechanisms)

2) Where did it start/point of origin?

3) What evidence supports your claim?

4) How can I recreate the scenario

What is ignition?

When gases burn to create a fire. Solids and flammable liquids don’t directly burn. They first turn into a gas, and then burn.

What is the chemistry of fire?

1) It is an oxidation reaction (a substance + oxygen = new substance)

2) It has an ignition temperature (the minimum temp. needed to ignite fuel)

3) It is an exothermic reaction gives of a heat of combustion ( the heat/energy liberated during combustion)

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What factors explain a fire?

1) How much energy is liberated (heat of combustion)

2) The rate/speed of oxidation reaction

3) What kind/type of fuel is consumed (Synthetic or natural? A lot or little? Gasoline?)

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What is oxidation?

Hydrocarbon + Oxygen = new substance

What is ignition temperature?

The minimum temperature required to ignite a fuel (spontaneously)

What is heat of combustion?

The heat liberated/involved during combustion

What is flashpoint?

The minimum temp. at which a liquid is heated enough to vaporize.

What is pyrolysis?

The decomposition of a solid into a gas (by heat/ that produces heat)

What is a flammable range?

The entire range of possible gas/vapor fuel concentrations in air that are capable of burning.

What is glowing combustion? What is another word for it?

Combustion on the surface of a solid fuel in the absence of heat high enough to pyrolyze fuel.

AKA. The glow at the air-face interface that has contact with the fire.

Smoldering.

What is spontaneous combustion?

Rather rare, but when a fire ignites due to the natural-heating processes in an unwell ventilated area.

What is combustion?

The rapid combination of oxygen with another substance which produce heat and light (aka. fire)

What is the difference between pyrolysis and combustion?

Combustion - when ignition occurs in the presence of oxygen

Pyrolysis - when ignition occurs without oxygen (the obj. is directly set ablaze by fire)

What is heat?

Thermal energy that produces fuel gases and causes ignition.

What are the 3 things required to initiate and sustain a combustion?

1) Oxygen (must be available in sufficient quantity)

2) Fuel (must be present)

3) Heat (must be applied to initiate and enough is generated to sustain combustion)

What are the 3 mechanisms of heat transfer?

Convection - heat is transferred through the movement of molecules in a liquid/gas (ex. cooking spaghetti)

Radiation - heat is transferred through electromagnetic waves (Ex. the sun burning you)

Conduction - heat is transferred through direct contact of solid obj. (Ex. you burn your hand touching a stove)

What are all Burn Patterns and Phenomenon (8)?

V-pattern, Alligatoring, Flashover, Rollover, Backdraft, Crazed Glass, Pour patterns, & Spalling of Concrete

What are V-Patterns?

A v-pattern caused by the thermal plume of fire → (may indicate) point of origin

What is an Alligatoring?

When material gets blisters or “scales” due to it burning at an intense heat.

What are pour patterns?

Pool of ignitable liquid that leave irregular patterns

What is crazed glass?

When glass cracks due to rapid cooling

What is the Spalling of Concrete?

When parts of concrete fall off due to intense heat.

What is Flashover?

Spontaneous ignition without a spark or a flame → objs. in space rapidly and simultaneously ignite.

It happens in enclosed spaces or when a fuel is exposed to thermal radiation in a compartment.

What is Backdraft?

A sudden exposure/increase in O2 after fire starts to extinguish → explosion

What is Rollover?

Gases ignite and rise to the ceiling setting it on fire

What are the Spurious vs. True Arson Indicators?

True Arson Indicators (7):


1. Multiple Points of Origin
2. Evidence of Other crimes
3. Ignitable fluids
4. Ignitable containers
5. Ignitable device
6. Trailers
7. Eye Witnesses

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Spurious are basically burn patterns & melted metal,

What are common injuries of victims of fire?

High Heat → skull fracture

Contraction of Muscles → bone fractures

Pugilistic posture → joint fractures

What signs indicate that a person has been affected by a fire?

* Carbon monoxide poisoning → pink organs
* Pugilistic posture (caused by shrinkage of body tissues ad muscles because of dehydration due to heat) → fighting position
* Presence of soot in lungs

Why does the arson investigator need to begin examination of a fire scene as soon as it has been extinguished?

Because accelerants quickly become absorbed/evaporate.

The supreme court said that the need to investigate an arson scene is greater than the need to get a search warrant.

What are you looking for in a fire investigation?

* Point(s) of origin
* Signs of accelerants (like gasoline or kerosene) → pour patterns. These signs may evaporate within a few days or hours.
* Parts of igniters: matches, parts of “Molotov’s Cocktail”, and electrical sparking devices
* Burn Patterns

How do you collect fire evidence from the scene? (What do you collect and what do you use?)

* Use the “sniffer” (vapor detector) to collect vapor samples and residues to take to the GC/MS for analysis
* Use airtight, glass containers (incase something is reactive)
* Freeze samples of soil or vegetation containing accelerants (so that they don’t degrade by bacterial action)
* Collect control specimens (they are similar to the evidence yet uncontaminated)

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How is GC/MS used in an arson investigation?

Gas Chromatograph is most reliable when detecting and characterizing flammable residues.

It will separate hydrocarbon components to produce a “snapshot” (individual chromatographic pattern characteristic)

* Majority of arsons initiated by petroleum distillates
* GC is only affective in comparison if the “snapshot” is registered.

What factors can contribute to the deviation of a fire from normal behavior?

Air flow currents & prevailing drafts and winds

What are 4 things that a fire lab is used for?

1) Test & explore ways to study fire

2) Help update fire prevention codes & procedures

3) Train firefighters to do their job safely

4) Help investigators solve arson crimes

What are things that arson investigators need to measure when they examine a fire?

Heat levels, energy released, smoke and oxygen levels

What are four skills/disciplines involved in effectively studying fire?

STEM skills

How is the scientific method applied to the study of fire?

1) You gather evidence and analyze it

2) Make a hypothesis based on the evidence gathered

3) Test out your predictions

4) Make a claim/story about how the fire started

What type of fuel release the most smoke and generate the most soot?

Synthetic/man-made fuels have 2-3x more stored per pound than a natural fuel → higher energy fuels generate more smoke

What are the Fire Development stages (in open spaces)

1) Ignition - heat + oxygen + fuel = fire

2) Growth - the fuel load will continue to burn and get bigger due to oxygen supply being unlimited (it is an open space)

3) Full Development - All combustible materials are ignited with enough oxygen (everything burns)

4) Decay - (usually longest stage) heat and fuel decrease until the fire goes out. Oxygen doesn’t decrease due to it being unlimited (air)

What is the fire behavior in a **closed room** (limited ventilation)?

Stage 1) heat transferred to gases → gases expand → gases become less dense than air around it.

Stage 2) Hot gases flow upward → **thermal plume** (column of smoke and hot gases; leave V-shaped pattern of soot & ash; created as gases are heated).

Stage 3) **A ceiling jet** is formed ( a thin layer of hot gases that begins to spreads out along the ceiling)

Stage 4) Hot gas layer forms (since ceiling jet begins to spread to the walls) & pressure increases

Stage 5) Combustion continues and consumes all available fuel, oxygen, and heat

Stage 6) Fire stops once it has consumed all the oxygen supply in room due to their being no outside supply.

How does ventilation affect the behavior of fire?

An opening in a structure can create ventilation.

It makes a fire bigger due to acting like a pump (hot gases exhaust while cooler air intake) - high pressure flows to low pressure.

Good ventilation → fire grows until Flashover occurs → everything pyrolyzes and ignites at the same time

Unventilated vs. Ventilated fire

Unventilated Fire: Soot is carried towards ceiling by thermal plume. Reach ceiling and walls = trapped → Hot gas layer forms at top and cooler, O2 rich air, stays at bottom → combustion ends once O2 supply is fully consumed

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Ventilated Fire: Thick black smoke begins to form around the openings - provides exhaust and release → Pyrolysis → keeps expanding due to unlimited supply of O2

What are some signs/hints that show where a fire started and spread?

Extensive damage → the more damaged, the closer to the fire

Burn patterns

Lines of demarcation - lines that show a border between two different fire effects on materials

Char - carbon material that is burnt and blackened (the more, the closer the fire was)

Pile of debris - materials that have all been burnt and melted (kind of like char)

Radiant heat - heat transmitted through radiation on materials → shows where furniture was

Melted plastics - can show causes of fire

Thermal patterns → show burn direction, decomposition & displacement

What are the 6 signs of arson? What 4 things must you be looking out for as you investigate a fire?

1) Was there a clear crime involved? Evidence of other crimes?

2) Were there any major fatalities or injuries?

3) Was there major property loss?

4) Was the cause of fire too complex to determine?

5) Are there any clear arson indicators?

6) Are you suspicious?

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1) Fire behavior - is it burning faster than normal? Are there multiple points of origin? is it burning lower than usual?

2) Incendiary Devices - any parts of igniters or trailers found?

3) Environmental Identifications - is there excessive fuel? Open entryways?

4) Suspicious behavior? Did the residents take out insurance on the property prior or quickly after the fire?

What is an Arson Dog? What are the commands and how do they show they found something?

K9 Arson dogs are dogs specialized in detecting accelerants at a fire scene. Although not fully concrete, but extremely reliable sources.

Commands are: Seek, show me!

The dog sits down near accelerant to ‘alert’

What must first responders do when they arrive at a fire scene?

1) Observe the fire and scene conditions (location, condition of victims, etc)

2) Exercise scene safety (safety hazards, structure hazards)

3) preserve the fire scene (seal off scene, documentation, etc0

4) Establish security and control

5) Coordinate interagency activities