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Flashcards in Fire And Arson Investigation Deck (25)
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1

What is the leading cause of arson?

Vandalism

2

Fire requires 3 elements

1. Heat
2. Fuel
3. Oxidizing agent

3

What is fire a result of?

An oxidation reaction

4

Oxidation

A chemical reaction between a substance and oxygen

5

"Slow" oxidation reaction

Processes such as rusting or bleaching

6

"Fast" oxidation reactions

Rapid release of beat such as combustion or fire

7

"Extremely fast" oxidation reaction

Explosions

8

Sequence of events during a fire

1. Incipient stage (growth)
2. Free-burning stage (development)
3. Smoldering stage (decay)

9

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

10

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)

11

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

12

Point of origin

•place where the fire started
•typically the site of greatest damage

13

Backwards Theory

Investigators work from exterior to interior and from areas of least damage to greatest damage

14

Burn patterns

Physical marks and char that remain after a fire

15

Burn pattern geometry

Shapes on the walls or floors may indicate handling of accelerant

16

"V" pattern

Accelerants from a container

17

Hourglass pattern

Pool of burning liquid

18

Pour pattern

Burn in the middle of a room

19

Trailer pattern

Burn pattern that resembles s flowing stream; liquid was spread from one location to another

20

Indicators of arson

1. Charring of floor surfaces
2. Containers
3. Odors

21

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

22

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

23

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

24

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

25

Metal paint and used for 2 reasons

1. Plastic will absorb compounds and may ruin sample
2. Cans are airtight and will preserve volatile vapors