Fire And Arson Investigation Flashcards
What is the leading cause of arson?
Vandalism
Fire requires 3 elements
- Heat
- Fuel
- Oxidizing agent
What is fire a result of?
An oxidation reaction
Oxidation
A chemical reaction between a substance and oxygen
“Slow” oxidation reaction
Processes such as rusting or bleaching
“Fast” oxidation reactions
Rapid release of beat such as combustion or fire
“Extremely fast” oxidation reaction
Explosions
Sequence of events during a fire
- Incipient stage (growth)
- Free-burning stage (development)
- Smoldering stage (decay)
Incipient stage (growth)
- begins with ignition of fire
- gases rise in the room
- oxygen dives to the bottom of the flames
- fire produces “V” pattern on vertical surfaces
Free Burning Stage (development)
- fire consumes more fuel and intensifies
- flames spread up and out
- dense layer of smoke and fire gases accumulate near ceiling (carbon monoxide)
- at 1100F all fuels in the room simultaneously ignore (flashover)
Smoldering Stage (decay)
- all fuel consumed and fire open flames disappear
- if oxygen enters, the spot and fire gases ignite with explosive force producing a backdraft
- pressure generated by a backdraft can cause significant structural damage and endanger lives
Point of origin
- place where the fire started
* typically the site of greatest damage
Backwards Theory
Investigators work from exterior to interior and from areas of least damage to greatest damage
Burn patterns
Physical marks and char that remain after a fire
Burn pattern geometry
Shapes on the walls or floors may indicate handling of accelerant
“V” pattern
Accelerants from a container
Hourglass pattern
Pool of burning liquid
Pour pattern
Burn in the middle of a room
Trailer pattern
Burn pattern that resembles s flowing stream; liquid was spread from one location to another
Indicators of arson
- Charring of floor surfaces
- Containers
- Odors
Charring of floor surfaces
Area of burned floor adjacent to unburied floor is a reliable sign of liquid accelerant (“v” pattern)
Accelerant can often be detected in the corners of a room or along the base of a wall
Containers
Liquid containers are evidence
If not damaged may be able to retrieve fingerprints left by arsonist
May indicate use of a liquid accelerant-even if melted
Odors (from liquid accelerant)
May evaporate quickly so evidence must be collected immediately
Contaminated areas can be detected with ultraviolet violet light or a hydrocarbon detector
Collection and preservation of arson evidence
Look for accelerant at the edges of burn pattern
Search for, identify, photograph evidence and note location in rough sketch
Photograph and comment condition of doors, windows, and locks
Collect debris in clean metal paint cans
Metal paint and used for 2 reasons
- Plastic will absorb compounds and may ruin sample
2. Cans are airtight and will preserve volatile vapors
