unit 14 explosion and fire

Question 1

explosives are

Answer 1

substances that undergo a rapid oxidation reaction with the production of large quantities of gases.
- This sudden buildup of gas pressure leads to the
explosion.

Question 2

spontaneous combustion is an

Answer 2

exothermic reaction caused by a natural heat-producing process with oxygen present.

Question 3

What are the elements that must be present if combustion is to be initiated and sustained?

Answer 3

1. a fuel must be present
2. oxygen must be available in sufficient quantity with
   the fuel
3. heat must be applied to initiate the combustion
4. sufficient heat must be generated to sustain the
   reaction

Question 4

How are most arson fires started?

Answer 4

petroleum distillates such as gasoline and kerosene

Question 5

What must a search of the fire scene by a forensic investigator focus on?

Answer 5

-The entire bomb site must be searched to recover any trace of detonating mechanism or any other item foreign to the explosion site.
* Objects located at or near the origin of the explosion must be collected for laboratory examination.
* All materials collected at bombing scenes must be placed in airtight containers such as clean paint cans

Question 6

How is a gas chromatograph used to identify an accelerant?

Answer 6

By comparing graphic peaks

Question 7

Oxidation

Answer 7

is the combination of oxygen with other substances
to produce new substances

Question 8

Pyrolysis

Answer 8

the chemical breakdown of solid organic matter by heat with the gaseous products combining with oxygen to produce a fire

Question 9

gas chromatograph

Answer 9

the most sensitive and reliable instrument for detecting and characterizing flammable residues.
- Separates the hydrocarbon components
* Produces a chromatographic pattern specific to each
petroleum product

Question 10

identify and name the 3 mechanisms of heat transfer

Answer 10

1. Conduction is the movement of heat through a solid object
2. Convection is the transfer of heat energy by the molecules within a liquid or gas
3. Radiation is the transfer of heat energy from a heated
   surface to a cooler surface by electromagnetic radiation

Question 11

what are the signs of arson?

Answer 11

1. Evidence of separate and unconnected fires
2. The use of “streamers” to spread the fire from one area to another
3. Severe burning found on the floor as opposed to the ceiling of a structure
4. Presence of accelerants
5. Presence of an ignition device

Question 12

Low explosives decompose at rates that vary up to

Answer 12

1,000m/sec
- Examples include black powder and smokeless powder

Question 13

In recent years, dynamite has been replaced commercially by

Answer 13

ammonium nitrate-based explosives

Question 14

dynamite is composed of

Answer 14

nitroglycerine, sodium nitrate, a good stabilizing agent, and pulp

Question 15

What is the single most important step in the detection and analysis of explosive residues?

Answer 15

the collection of appropriate samples from the explosion scene.

Question 16

After bomb-scene debris has been examined microscopically, what is the next step?

Answer 16

it is rinsed with acetone to separate the debris from explosive material.

Question 17

What produces the violent physical disruption associated with an explosion?

Answer 17

The sudden build-up of expanding gas pressure

Question 18

What are the ingredients required to create a low explosive?

Answer 18

a fuel and an oxidizer

Question 19

Combustion

Answer 19

is rapid oxidation, accompanied by production of noticeable heat and light.

Question 20

difference between exothermic and endothermic reaction

Answer 20

exothermic- heat energy is liberated
endothermic: heat is absorbed from surroundings

Question 21

The speed at which an explosive decomposes determines whether

Answer 21

it is classified as high or low explosive

Question 22

Common high explosives include

Answer 22

1. ammonium nitrate-based
2. water gels, emulsions, and ammonium nitrate/fuel oil
   (ANFO) explosives

Question 23

primary explosives vs secondary explosives

Answer 23

primary: are ultrasensitive to heat, shock, and friction.
secondary: normally constitute the main charge of a high explosive

Question 24

the most obvious characteristics of a high or contained low explosive is the presence of

Answer 24

a crater at the origin of the blast.

Question 25

a search of the fire scene by a forensic investigator must focus on

Answer 25

findings the fire’s origin

Question 26

Ammonium Nitrate/Fuel Oil (ANFO)

Answer 26

is one of the most widely used explosives for civilian purposes. Its main advantages are its low price and simple method of production.

Question 27

ion mobility spectrometer

Answer 27

A device widely used to screen objects for the
presence of explosive residues

Question 28

Unconsumed explosives are identified by either

Answer 28

infrared spectrophotometry or X- ray diffraction

Question 29

Recovered debris may be thoroughly rinsed with organic solvents and analyzed by testing procedures that include:

Answer 29

• color spot tests
• thin-layer chromatography
• gas chromatography/mass spectrometry.

Question 30

Streamers are trails of flammable material, such as

Answer 30

gasoline or paper, spreading outward from a fire’s
point of origin in order to cause the fire to move
rapidly from one room to another

Question 31

for a fire to occur…

Answer 31

a fuel must be present, oxygen must combine with the fuel and heat, sufficient to start and maintain the reaction

Question 32

Factors that influence the speed of the reaction include

Answer 32

the physical state of the fuel and the temperature.