Forensic Chemistry: Fire and Explosives Flashcards
(14 cards)
What is the fire triangle?
Fuel
Heat
Oxygen
What are ignitable liquids versus accelerants?
Ignitable liquid
* Any liquid that can ignite and burn
* Has a low flash pint and high flammability
Accelerant
* A fuel that is used to Intentionally initiate or increase the intensity or speed of spread of fire
* Liquids: gas, isopropyl
* Gases: butane, propane natural gas
* Solids: paper, fireworks, road flares, black powder
What does it mean for something to be ignitable, flamable, and combustible?
Fire scene terminology 1
Ignitable
* Any substance that can catch fire and keep burning under the right conditions
Flammable
* Material that ignite and burn easily at normal temperatures
* Gas and alcohol
Combustible
* Requires higher temperatures to ignite and then burn
what are ignition temperature, flashpoint, flashover, and explosive limit?
Ignition temperature
* Minimum temperature at which a solid will start burning
Flashpoint
* Minimum temperature at which a liquid will start burning
Flashover
* The stage in a fire in which everything in the room starts burning
Explosive limit
* Range of vapor concentration in the air in which if it is ignited it will explode
What are the main goals of forensic fire scene investigation?
- Where did it start?
- Why did it start?
- How did it start?
What are the steps in forensic fire examination?
Scene examination
* documenting patterns and damage
* identifying point of origin
* collection evidence
Lab examination
* preliminary examination
* extraction
* instrument analysis
* interpretation
* reporting
Determining the cause of the fire
* Deliberate, accidental, natural, undetermined
What is the explosion pentagon?
A fire becomes an explosion when these five things are present:
1. confinement
2. heat
3. fuel
4. oxygen
5. dispersion
What is an explosion and its types?
Explosion
A rapid release of energy resulting from a chemical reaction, creating heat, gas, and pressure
Explosive material
Compound or mixture which decomposes or rearranges very quickly after having been
exposed to heat or shock, producing large quantity gas and heat
Chemical explosion
An extremely rapid reaction from products of a chemical reaction involving explosive material
What are the types of explosives?
Chemical –> low and high
High explosives –> primary high and secondary high
What is a low explosive?
Slow burn; deflagration
Black powder (ex. foreworks)
Smokeless powder
Flash powder
Pyrotechnics
What is a high explosive?
Primary high explosives
* Sensitive, used to trigger or detonate secondary explosives
Secondary explosive
* Fast reaction, detonation with a shockwave, main explosive charge
What are deflagration and detonation?
Deflagration
* The reaction spreads by thermal conduction (heat transfer) and diffusion of reactants
* subsonic
* low-pressure wave
* slower energy release
Detonation
* The shockwave drives the reaction, creating an explosive release of energy
* (a primary explosive triggers the detonation of a secondary explosive)
* supersonic
* high-pressure shockwave
* rapid energy release
What are the detection techniques?
Chemical tests
* Wide range of colorimetric kits available for detection of explosive materials
Canines
* Dogs trained to detect vapors from explosives
Field instrumentation
* Portable instruments are more sensitive and specific than chemical techniques
What are the main instrumental analysis techniques?
Spectroscopic techniques and chromatographic techniques with mass spectrometry
- GC-MS
- FTIR
