Forensics Exam II: Ch. 17 - Arson and Explosion Investigation

Fire

oxygen, fuel, and heat

Combustion

ignition point is reached

Glowing Combustion

occurs on surface where fuel is

Flash Point

lowest temperature liquid needs to turn into a vapor and flashes when exposed to an open flame

Auto Ignition

lowest temperature fuel spontaneously ignites in normal atmosphere without external source

Conduction

transfer of heat through objects, poor conductors are insulators, fires usually travel through metal

Convection

transfer of heat within a liquid or gas

Radiation

transfer of heat through electromagnetic radiation, if an e object is too close to a fire it could burst in flames

Locating Fire’s Origin

origin is most likely the lowest point and shows the most intense characteristics of burning

Signs of an Accelerant Fire

V-pattern, irregular burn path on floor, separated and unconnected fires

Collecting Arson Evidence

collect ash, soot, and porous materials

Storing Arson Evidence

store in paint cans or wide mouth glass jars, never use plastic

Detect and Identify Hydrocarbon Residues

1. Heat container containing arson evidence

2. Residues and debris are stripped and trapped in containers enclosed airspace

3. Vapor is removed with syringe and injected into chromatograph

4. Vapor is separated into components and recorded on a chromatogram

Explosion

caused by rapid oxidation and a build up of gas pressure

Commercial Explosives

black powder, smokeless powder, pipe bombs, ammonium nitrate

Homemade Explosives

ANAL, TATP (Triacetone Triperoxide), German Dark Pyrotechnic Aluminum

Military Explosives

TNT, Dynamite, RDX

Collecting Evidence

1. Entire scene must be searched

2. Recover detonating device and other foreign objects

3. Any objects found must be collected

4. Collect loose soil and debris within a 100ft radius (3 tbl spoons of surface soil, quarter inch)

Analyzing Evidence

1. Examine debris microscopically for unconsumed particles

2. Debris may be rinsed with organic solvents

3. Can use color tests, thin-layer chromatography, and gas chromatography/ mass spectrometry

4. Confirmation Identification tests are used on unexploded materials with infrared spectrometry