Lecture 16: Fire and Explosions

Question 1

What is fire in relation to oxidation?

Answer 1

Fire is a form of oxidation where oxygen combines with other substances, releasing energy in exothermic reactions.

Question 1

Describe the energy manifestation in oxidation reactions.

Answer 1

Energy in oxidation reactions can manifest as heat and light, with reactions releasing more energy than needed to start.

Question 2

Explain the concept of flash point.

Answer 2

Flash point is the lowest temperature at which a liquid generates sufficient vapor to ignite and burn.

Question 3

What is combustion?

Answer 3

Combustion is a chain reaction requiring fuel vapor, oxygen, and heat to initiate and sustain fire.

Question 4

What are the heat transfer mechanisms in fire?

Answer 4

Heat transfer in fire involves conduction through solids, radiation via electromagnetic radiation, and convection through fluid movement.

Question 5

What role does oxygen play in combustion?

Answer 5

Oxygen must be present in sufficient quantity to combine with the fuel for combustion to occur.

Question 6

Why is heat necessary in combustion reactions?

Answer 6

Heat is essential to initiate and sustain combustion reactions by raising the temperature of the fuel to its ignition point.

Question 7

In what physical state does combustion to produce a flame typically occur?

Answer 7

Combustion to produce a flame usually occurs when the fuel is in a gaseous state.

Question 8

What is the flash point of a liquid fuel, and why is it significant?

Answer 8

The flash point is the temperature at which a liquid fuel vaporizes enough to ignite; it indicates the temperature needed for combustion.

Question 9

Explain the process of glowing combustion or smoldering.

Answer 9

Glowing combustion occurs at the fuel-air interface, seen in examples like a cigarette or embers of a fire, where slow oxidation takes place.

Question 10

What challenges do arson investigations pose?

Answer 10

Arson investigations pose challenges due to meticulous planning, absence during the act, and extensive destruction.

Question 11

What is the role of criminalists in arson investigations?

Answer 11

Criminalists detect and identify chemical materials at the scene and reconstruct igniter mechanisms.

Question 12

What does determining the cause of a fire require?

Answer 12

Determining the cause of a fire requires an investigator with specialized training and experience in fire investigation.

Question 13

What is fire in terms of chemical reactions?

Answer 13

Fire is a form of oxidation, involving the combination of oxygen with other substances to produce new substances.

Question 14

What is an exothermic reaction in the context of oxidation?

Answer 14

Oxidation reactions release more energy than needed to start the reaction, known as exothermic reactions.

Question 15

What are some indicators of arson in a fire scene?

Answer 15

Indicators include separate fires, streamers to spread fire, and irregular patterns from accelerant pouring.

Question 16

How can the probable origin of a fire be determined?

Answer 16

Fires typically move upward, with the lowest point showing the most burning indicating the likely origin.

Question 17

What type of residues suggest the use of flammable liquids in arson cases?

Answer 17

Severe burning on the floor suggests flammable liquid use, as they are usually not fully consumed in a fire.

Question 18

What are some ignition devices that arsonists may use to start fires?

Answer 18

Arsonists may use matches, burning cigarettes, firearms, or other ignition devices to start fires.

Question 19

How are accelerant residues collected at the fire’s origin for analysis?

Answer 19

Ash, soot, and porous materials with residues are gathered in airtight containers like paint cans or glass jars for analysis.

Question 20

How should ash, soot, and porous materials with potential accelerants be stored?

Answer 20

In airtight containers like new paint cans or wide-mouth glass jars, avoiding plastic containers.

Question 21

What are recommended for detecting flammable liquid residues at a fire scene?

Answer 21

Using a vapor detector (sniffer) or trained canines.

Question 22

Why is substrate control important when collecting materials suspected of containing volatile liquids?

Answer 22

To have uncontaminated controls from another area of the scene for comparison and analysis.

Question 23

How are accelerant residues from fire scene debris recovered in the laboratory?

Answer 23

By heating the airtight container holding the sample to drive off volatile residues, then analyzing the vapor collected.

Question 24

What role does gas chromatography play in analyzing flammable residues in fire scene evidence?

Answer 24

Gas chromatography is used to separate and analyze flammable residues, providing a characteristic chromatographic pattern for different petroleum products.

Question 25

What should be the timeline for commencing an arson investigation?

Answer 25

Arson investigation should start immediately after extinguishing the fire.

Question 26

What are some common petroleum-based accelerants used by arsonists?

Answer 26

Arsonists often use petroleum-based accelerants like gasoline to start fires.

Question 27

What is the primary focus of the investigation in arson cases?

Answer 27

The investigation mainly centers on determining the origin of the fire.

Question 28

How can irregular patterns on the floor indicate arson?

Answer 28

Irregular patterns from accelerant pouring suggest arson as a cause of the fire.

Question 29

What type of burning pattern suggests the use of flammable liquids in arson cases?

Answer 29

Severe burning on the floor, rather than the ceiling, indicates the use of flammable liquids in arson.

Question 30

How can gas chromatographic peaks be utilized in fire investigations?

Answer 30

Gas chromatographic peaks can help identify the accelerant used to start a fire by comparing sample patterns to chromatograms of accelerant standards.

Question 31

What tool is used to identify gasoline patterns and accelerants in fire investigations?

Answer 31

Searchable libraries like the Ignitable Liquids Reference Hydrocarbon Collection (ILRC) are used to identify gasoline patterns and accelerants.

Question 32

How are complex chromatographic patterns simplified in fire investigations?

Answer 32

Complex chromatographic patterns are simplified using Gas Chromatography-Mass Spectrometry (GC/MS).

Question 33

What is the role of GC/MS in confirming gasoline-like patterns in residue samples from fire scenes?

Answer 33

GC/MS is used to confirm gasoline-like patterns in residue samples from fire scenes, which may initially resemble gasoline patterns.

Question 34

How are explosives classified based on their decomposition speed?

Answer 34

Explosives are classified as high or low based on their decomposition speed, with low explosives like black powder and smokeless powder being common.

Question 35

How are primary explosives characterized?

Answer 35

Primary explosives are ultra-sensitive to heat, shock, or friction and are major ingredients in blasting caps or primers for detonating other explosives.

Question 36

What defines high explosives?

Answer 36

High explosives are defined by their speed of decomposition causing container walls to fragment and fly outward.

Question 37

What distinguishes secondary explosives?

Answer 37

Secondary explosives are relatively insensitive to heat, shock, or friction. They burn rather than detonate if ignited in small quantities in open air.

Question 38

What is the process of detonation in high explosives?

Answer 38

Detonation is characterized by extremely rapid decomposition producing a supersonic shock wave and a blast effect with outward rush of gases at speeds up to 7,000 miles per hour.

Question 39

What are examples of military high explosives?

Answer 39

Examples include RDX, often in the form of C-4, and Triacetone triperoxide (TATP), a homemade explosive used by terrorist organizations.

Question 40

Why is it important to search the entire bomb site systematically?

Answer 40

To recover any detonating mechanism or foreign items that may provide crucial evidence.

Question 41

Why is the preservation of loose soil and debris from the crater’s interior critical?

Answer 41

To allow for analysis that may reveal important information about the explosive device and its origin.

Question 41

What is the purpose of collecting objects near the explosion’s origin for laboratory examination?

Answer 41

To analyze them for evidence that can help in the investigation, such as identifying potential explosives.

Question 42

How can objects be screened for explosive residues at a bomb site?

Answer 42

By using ion mobility spectrometry, a technique that can detect the presence of certain substances indicative of explosives.

Question 43

Why is it necessary to package debris and articles from different areas separately?

Answer 43

To prevent contamination and ensure that the evidence remains intact and reliable for analysis.