Forensics arson

Arson

The criminal act of deliberately setting a fire

Arson often presents…

Complex and difficult circumstances to investigate

What does arson crimes often leave behind?

Burned or charred evidence and wet conditions (from attempts to eradicate the flames)

The goal of a fire investigator

To detect and identify relevant chemical materials, identify igniters and reconstruct the events that led to the fire

Upon arriving at the scene, the investigator should note:

- Presence, location, and condition of victims
- flame and smoke conditions (direction, height, location)
- status of alarms, sprinklers
- unusual characteristics of scene
- conditions of the structure: Lights, windows, doors

Fire

A product of the process during which oxygen is united with some other substances to produce noticeable quantities of heat and light (a flame)

Oxidation

A combination of oxygen with other substances to produce new substances

Combustion

When a rapid combination of oxygen and other substances combine accompanied by the generation of heat and light to form a flame

What happens once combustions begins?

Enough heat is liberated to keep the reaction going by itself. A fire becomes a chain reaction, absorbing a portion of its own heat to generate more heat

How things ignite

When fire is held to the paper…
1. Molecules that are bound closely to one another on the surface are…
2. …loosened by the heat. They move further apart from one another becoming a gas
3. The gas molecules combine with oxygen molecules in the air and the paper begins to burn

Three requirements must be satisfied to initiate and sustain combustion

1. A fuel must be present
2. Oxygen must be available in sufficient quantity to combine with the fuel
3. Heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction

When arson investigators arrive at the scene…

They begin by searching for the point of origin (where the fire began)

Pattern in which fires burn

“V” pattern of char/soot that leads to origin of fire

Once the point of origin is determined…

Investigators then focus their attention on the search for accelerants or ignition devices

How do investigators detects accelerants?

- Portable hydrocarbon detectors
- accelerant sniffing dogs
- identifiable pour patterns (that are then tested)

When specimens are collected from a crime scene…

They should be packaged immediately in airtight containers so possible residues are not lost through evaporation

Common reasons for arson crimes

- insurance fraud
- crime concealment
- pyromania
- revenge

Why is arson divided into degrees?

Depending sometimes on the value of the property but more commonly on its use and whether the crime was committed in the day or night

First-degree arson

Burning an occupied structure such as a school or a place where people are normally present

Second-degree arson

Burning an unoccupied building such as an empty barn or an unoccupied house or other structure in order to claim insurance on such property

Third-degree arson

Burning an abandoned building or an abandoned area, such as a field, forest, or woods

How does terrain effect forest fires?

Fire moves faster on steep slopes

John Orr

Was a firefighter; wrote a book called “Point of Origin”; known as the “Pillow Pyro”

If humidity is low, will the fire’s characteristics most likely increase or decrease?

Decrease

How is arson evidence packaged?

Immediately placed in an airtight container