Intro to Forensics -- Chapter 17: Arson and Explosives

arson

the criminal act of deliberately setting fire to property

fire is a type of _______ reaction

oxidation

energy

the ability to do work

exothermic reactions

reactions that release energy

endothermic reactions

reactions that absorb energy

ignition point

minimum temperature needed to spontaneously ignite fuel

heat of combustion

the heat and light released when a substance burns

what 3 factors are required to initiate and sustain a fire

fuel, oxygen and heat

flash point

the lowest temperature at which a liquid produces enough vapor to burn

pyrolysis

the decomposition of organic matter by heat

glowing combustion

burning located at the fuel-air interface

what are the three mechanisms of heat transfer

conduction, radiation, and convection

conduction

the movement of heat through a solid object

insulators

poor conductors

radiation

the transfer of heat energy by electromagnetic radiation

convection

the transfer of heat energy by the movement of molecules within a liquid or gas

most arsons are started with...

petroleum-based accelerants

the search of the fire scene must focus on finding...

the fire's origin

how do you find a fire's origin?

a fire has a tendency to move in an upward direction in a V shape

flashover

occurs when all the combustible fuels simultaneously ignite to engulf the entire structure

combustible liquids are _________ entirely consumed in a fire

rarely

3 multiple choice options

sensitive portable vapor detector (sniffer)

used to search for traces of flammable liquid

porous materials

materials that have tiny openings that can absorb liquids

how is fire scene evidence stored?

airtight containers such as new paint cans or wide-mouth glass jars, leaving an airspace to remove samples

substrate control

uncontaminated control specimens from another area of the fire scene

what is the most common ignition device?

matches

headspace

room left in a container for the material to expand

gas chromatography

separates the fire evidence material into its components and each peak is recorded on the chromatogram

vapor concentration technique

a charcoal strip is placed in the airtight debris container when it is heated, the strip absorbs the vapor, the strip is washed with a solvent, the solvent is then injected into the gas chromatograph

petroleum distillates

materials derived from crude oil, such as gasoline and kerosene

gas chromatography comparison

comparing materials recovered from fire-scene to known flammable liquids

ignitable liquids reference hydrocarbon collection

searchable library of complex chromatographic patterns

explosives

substances that undergo a rapid oxidation reaction, producing large quantities of gases

low explosives

decompose slowly, often confined to a container like a pipe

black powder

type of low explosive, a mixture of potassium or sodium nitrate, charcoal, and sulfur

smokeless powder

type of low explosive, consists of nitrated cotton or nitroglycerin and nitrocellulose

deflagration

the speed of decomposition in a low explosive

high explosives

decompose much faster, can be separated by primary and secondary explosives

primary explosives

ultra-sensitive to heat, shock, or friction and provide the major ingredients found in blasting caps or primers used to detonate other explosives

secondary explosives

must be detonated by a primary explosive, relatively insensitive to heat, shock, or friction and will normally burn rather than detonate

examples of secondary explosives

dynamite, TNT, PETN, and RDX.

detonation

the speed of decomposition of high explosives

triacetone triperoxide (TATP)

a homemade explosive, made by combining acetone and peroxide in the presence of an acid

RDX

the most widely used explosive in the military

ion mobility spectrometer

screening test for the presence of explosive residues

what are some alternative tests for collected debris?

color spot tests, thin-layer chromatography, and gas chromatography/mass spectrometry

what is the confirmatory test for fire-scene evidence?

infrared spectrophotometry

which is available in commercial form as fertilizer?

ammonium nitrate

what is the major advantage of using the vapor concentration technique with gas chromatography?

high sensitivity for detecting volatile residues

a fuel can only achieve combustion in the _________

gaseous state

3 multiple choice options

most explosives can be recovered from debris for future study by being rinsed with

acetone

what is the rapid combination of oxygen with a fuel, which produces a noticeable release of energy?

combustion

arson investigators must work quickly to collect evidence at a fire scene because

all of the above

3 multiple choice options

telltale signs of arson include...

all of the above

3 multiple choice options

which is an initiating explosive often used in detonators?

lead azide

modus operandi

an offender's pattern of operation

hydrocarbon

compounds composed of only carbon and hydrogen

oxidizing agent

a substance that supplies oxygen to a chemical reaction

safety fuse

a cord containing a core of black powder, used to carry a flame at a uniform rate to an explosive charge

smokeless powder single base

an explosive consisting of nitrocellulose

smokeless powder double base

an explosive consisting of a mixture of nitrocellulose and nitroglycerin

detonating cord/primacord

a cordlike explosive containing a core of high-explosive material, usually PETN

burning methane for the purpose of heating water to produce steam in order to drive a turbine is an example of converting ___________ energy to ___________ energy

chemical, mechanical

3 multiple choice options