Lecture 16: Fire and Explosions Flashcards

1
Q

What is fire in relation to oxidation?

A

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

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1
Q

Describe the energy manifestation in oxidation reactions.

A

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

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2
Q

Explain the concept of flash point.

A

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

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3
Q

What is combustion?

A

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

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4
Q

What are the heat transfer mechanisms in fire?

A

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

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5
Q

What role does oxygen play in combustion?

A

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

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6
Q

Why is heat necessary in combustion reactions?

A

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

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

Explain the process of glowing combustion or smoldering.

A

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

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10
Q

What challenges do arson investigations pose?

A

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

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11
Q

What is the role of criminalists in arson investigations?

A

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

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12
Q

What does determining the cause of a fire require?

A

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

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13
Q

What is fire in terms of chemical reactions?

A

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

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14
Q

What is an exothermic reaction in the context of oxidation?

A

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

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15
Q

What are some indicators of arson in a fire scene?

A

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

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16
Q

How can the probable origin of a fire be determined?

A

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

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17
Q

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

A

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

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18
Q

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

A

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

19
Q

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

A

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

20
Q

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

A

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

21
Q

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

A

Using a vapor detector (sniffer) or trained canines.

22
Q

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

A

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

23
Q

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

A

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

24
Q

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

A

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

25
Q

What should be the timeline for commencing an arson investigation?

A

Arson investigation should start immediately after extinguishing the fire.

26
Q

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

A

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

27
Q

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

A

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

28
Q

How can irregular patterns on the floor indicate arson?

A

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

29
Q

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

A

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

30
Q

How can gas chromatographic peaks be utilized in fire investigations?

A

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

31
Q

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

A

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

32
Q

How are complex chromatographic patterns simplified in fire investigations?

A

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

33
Q

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

A

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

34
Q

How are explosives classified based on their decomposition speed?

A

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

35
Q

How are primary explosives characterized?

A

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

36
Q

What defines high explosives?

A

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

37
Q

What distinguishes secondary explosives?

A

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

38
Q

What is the process of detonation in high explosives?

A

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.

39
Q

What are examples of military high explosives?

A

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

40
Q

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

A

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

41
Q

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

A

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

41
Q

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

A

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

42
Q

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

A

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

43
Q

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

A

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