Name ______________________________________________ Period ______________ Date ______________________
Arson
What is Fire?
•
Rapid ___________________________ of substances through ___________________________
reactions with the release of energy and the formation of chemical products
•
___________________________ reactions between fuel and an oxidant
–
Energy is release in the form of ___________________
What is a Flame?
•
Hot _____________________ produced from the combustion of fuel
•
Gases emit visible ____________________ when high energy electrons from heated
molecules cool to a lower energy
What is the primary oxidant in fires of forensic interest?
•
___________________________
What are the most common fuels in fires of forensic interest?
•
_________________________________
Where does the energy generated during the burning originate?
•
Potential energy in the ________________________ _____________________ of the fuel molecules
•
Potential energy is then converted to
–
___________________________
–
___________________________
–
___________________________
–
___________________________________ energy
Fire Tetrahedron
1
Heat
•
Auto-ignition temperature (kindling point)
–
___________________________ temperature at which a substance will spontaneously
ignite ___________________________ an external source of ignition (spark)
•
A compound can ________________________________ combust once the
___________________________ is high enough to overcome the activation energy necessary
for a combustion reaction to occur
•
Flash point
–
Lowest ___________________________ of a fuel at which it will vaporize to form an
ignitable mixture with air that will combust in the presence of an ignition
source
Fuel
Gasoline
Diesel Fuel
Vegetable Oil
Paper
Wood
Methane
Ethanol (70%)
Flash Point (oC)
-43
62
327
232
300
-221
16
Auto-Ignition Temp. (oC)
246
210
650
450
300-450
537
363
Oxidants
•
•
Oxygen (Oxidizer)
–
Transfers oxygen atoms or removes ___________________________
–
Required for a __________________ to begin and continue
Air-fuel ratio
–
Relative amounts of oxygen and fuel in a gaseous mixture air is only
___________ oxygen
•
Flammability limits
–
Threshold limits of ___________________________ mixture that are required for
combustion
–
Lean mixture: too much _________________________ or too little _____________________
–
Rich mixture: too much _____________________ or too little _________________________
2
Oxygen (oxidizer)
•
In explosives, the oxidizer is _________________ atmospheric oxygen
–
Cant supply oxygen fast enough to generate an extremely fast
chemical _________________________
Fuel
•
Any material that stores chemical energy that can be extracted through
________________________________ reactions
•
Combustible materials must first be _________________________ enough for combustible
gases to be given off to mix with oxygen
Fire Suppression
Tetrahedron
components
Heat
Oxidant
Fuel
Chain reaction
Suppression or removal
Water cools fire by absorbing energy to change state
Carbon dioxide or sodium bicarbonate remove oxygen
Physically isolating the fuel source or interrupting the flow of
fuel into the fire
Halon fire extinguisher – at high temperatures halogens
become radicals that remove chain-continuing radicals and
interrupt combustion
Stages of a fire
3
Heat Release Rate
•
Rate at which heat is _________________________________ during a fire
•
Investigators consider the variables that can contribute to HRR
–
_________________________ of area burning
–
_____________________________ of the fuel
–
______________________________ content of fuel
–
_________________________ ___________________ available for combustion
–
______________________________ of burning materials
–
_________________________ for transfer
–
How _____________________________ the materials burned
The Investigation…
•
First
–
•
Determine the _________________________ of the fire
Second
–
Determine if the fire arose _______________________________,
___________________________, or _____________________________
•
Arson
–
Criminal act of _______________________________ setting a fire without lawful
consent
Arson Crimes
•
Covering a homicide
•
Destroying property for insurance fraud (most common)
•
Eliminating questionable records
•
Hate crimes
•
Revenge
•
Terrorism
4
At the crime scene…
•
Look for “_________________________” components of fire tetrahedron
–
Most prove one or more components have been inappropriately or criminally
altered
•
_________________________ to find natural or accidental cause is not acceptable legal
argument for arson as cause
•
Work from least damaged to most damaged areas
•
Document the scene with notes, pictures, and videos
•
Determine the point of _________________________
•
Collect evidence
•
Interview witnesses
•
Determine the heat _________________________
Accelerants
•
Compounds (often hydrocarbons) which facilitate ______________________________ and/or
growth of a fire, but do not necessarily serve as fuel
•
Causes fire to start _________________________ and burn _________________________
•
Consume fuel in an ____________________________ pattern
Interview Firefighters
Clues…
•
Multiple points of origin
•
Presence of accelerants
•
Unusual burn patterns
•
Quantity and color of smoke
•
Disabled fire suppression systems
•
Unusual ventilation arrangements
•
Condition of fire scene
5
Color of the smoke
•
Gasoline will give off a yellow flame and thick black smoke
•
Wood will give off a yellow or red flame and a gray or brown smoke
Supply of oxygen
•
Windows or doors propped open
•
Unusual openings in walls or ceiling
Burn Patterns
•
Linear burn pattern
–
•
Narrow V-shaped pattern
–
•
Accelerant poured over floor ____________________ underneath the floor
U-Shaped pattern
–
•
Fire _________________________ than normal – possible accelerant used
Inverted cone burn pattern
–
•
Accelerant poured over ______________________ then ignited
Pool of origin; pool of _______________________________
Wide V-shaped pattern
–
______________________ burning fire
Tools & Techniques
•
Hand-held _____________________________ detectors
•
Photographs
•
Personal observations – “watch the watchers”
Determining point of origin
•
NOT looking for deepest charring
•
Identify fire _________________________
•
Determine the path of the spread of the fire
•
Witness information
6