Arson/Explosives Flashcards
A shock wave is produced when:
A wave front exceeds the speed of sound
A sudden, rapid, and often violent release of hot expanding gases is called
an explosive (explosion??)
All of these can be used to initiate an IED except:
TNT
Deflagration is an oxidative decomposition in which the propagation speed is ____ than the speed of sound
slower
What determines how much residue of an accelerant will be left and for how long?
How volatile the accelerant is
What is the flash point?
The lowest temperature at which a liquid will produce enough vapor to burn
What is the most common instrument used in fire and explosive analysis?
GC/MS
What is the most common container used to collect fire debris evidence?
unlined paint can
When collecting charred samples from the point of origin to help determine which type of accelerant used, what is also important to collect?
control samples
Accelerants
any substance that is used to start or sustain a fire
Accelerants are
easily vaporized, highly exothermic, and support combustion
To initiate and sustain a fire, the following are required:
A fuel (vapor) must be present.
Oxygen must be available in sufficient quantity to combine with the fuel.
Heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction
Fire has a tendency to move _____
upwards
If an arson is suspected then _______ need to be collected from around the point of origin
about two to three quarts of the ash and soot debris
Neat, ignitable liquids
unburned accelerant residue
Headspace method
the evidence container is generally heated, vapor above the matrix or the headspace can then be sampled with a gas-tight syringe and injected into the gas chromatograph
Adsorption method
relies on the use of charcoal or Tenax®, a polymer resin used to trap volatiles and semi-volatiles
Solvent extraction
The evidence container is opened and a small amount of a solvent is added
Steam distillation
accelerant residue and water are steamed and distilled, the steam will heat and carry over accelerant residues
One method of making illicit methamphetamine is called “shake and bake”. During the process, bottles like the one shown become hot enough to start fires. What is our source of ignition energy?
exothermic chemical reaction
What is the purpose of headspace analysis in fire evidence?
It helps eliminate background noise from the burned debris
Low explosives
deflagrating and only detonate when confined
High explosives
insensitive but stable, require an initiator to detonate
Primary explosives
Explosives that are ultra-sensitive to heat, shock, or friction
Secondary explosives
Explosives that are relatively insensitive to heat, shock, or friction
You inflate a balloon until it ruptures. This release of energy would be classified as
Explosion
Identify the common secondary explosives
TNT
ANFO
Semtex
The primary challenge of explosives analysis is
The device and its residues are often very difficult to locate
Which method provides the fastest, easiest method of explosives residues identification, even if it is somewhat susceptible to false positives?
Ion Mobility Spectronomy
Autoignition Temperature
Spontaneous ignition
All fires have
point of origin and means of ignition
What do we use to determine the point of origin?
“V” pattern
Low position
Deep charring
Near source of ignition energy
Spark
electrical discharge
Types of heat (ignition energy)
Radiation
Electrical resistance
Non-combustion exothermy
Friction
Ignitable Liquids
Liquid fuel with a low flash point; highly exothermic
Common Ignitable Liquids
Kerosene
Diesel
Gasoline
Coleman Fuel
Ethyl Alcohol
Isopropyl
Incendiary
Deliberate ignition
Deflagration
combustion through subsonic heat transfer
Detonation
combustion through supersonic pressure front
Explosion
rapid, expansive release of stored energy producing a shock wave
Combustion
oxidation producing gas, heat, and/or light
Secondary Explosives
Detonate in response to supersonic pressure wave
Backdraft
Eruption of fire caused by oxygen rushing back into an engulfed room
Convection
transfer of heat by a circulating medium, usually air or liquid
Pyrolysis Zone
zone where the components of the wax are driven into the gas phase and start to degrade
