Lecture 3: Arson Investigation Flashcards

1
Q

Define molecules.

A

A molecule is formed when two or more atoms join together by chemical bonds, e.g. O2 (diatomic molecule).

Examples include air (a mixture) and water (a compound).

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2
Q

Define compounds

A

A compound is a molecule that contains at least two different elements, e.g. H2O.

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3
Q

Define mixtures

A

A mixture is made from two or more substances, e.g. air (78% N2, 21% O2, 0.033% CO2).

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4
Q

What is a combustion reaction?

A
  • Rapid oxidation
  • Produces carbon dioxide and water
  • Exothermic: Releases excess energy as heat
  • Example: CH4 + 2O2 → CO2 + 2H2O.

Example: CH4 + 2O2 → CO2 + 2H2O.

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5
Q

Complete combustion VS Incomplete combustion

A

Complete

  • Enough oxygen
  • Non-toxic products
  • E.g. natural gas in stove: intense blue, no smoke

Incomplete

  • Limited oxygen
  • Toxic products (Carbon monoxide)
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6
Q

What is the fire triangle?

A

Fuel, heat, and oxygen.

Removing any one of these elements can extinguish a fire.

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7
Q

How can fire be extinguished?

A
  • Removing any element in the fire triangle
    • Remove fuel
    • Remove heat: cooling with water
    • Remove oxygen: add inert gas (CO2 fire extinguisher), separation (fire blanket)

This is a common method used by firefighters.

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8
Q

Where is fuel obtained?

A

Combustible material

  • Solid fuels e.g., wood, coal, charcoal.
  • Liquid fuels e.g., gasoline, diesel
  • Gaseous fuels e.g., natural gas, hydrogen
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9
Q

Where is oxygen obtained?

A
  • Air (21% oxygen)
  • Oxidizers, e.g. nitrates, peroxides
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10
Q

What factors indicate the point of origin of a fire?

A
  • Intense location of burning
  • Low point in the building.
  • Smoke/damage shows V pattern
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11
Q

How do arsonists tamper with the fire triangle?

A
  • More accelerants to increase fuel load
  • Use match/lighter as heat source
  • Open windows to increase oxygen
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12
Q

What are common motives for arson?

A
  • Revenge
  • Vandalism
  • Profit
  • Crime concealment
  • Excitement
  • Extremism
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13
Q

What are indicators of arson?

A
  • Use of accelerants
  • Multiple points of origin
  • Disabled fire protection devices
  • Forced entry
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14
Q

What are the four stages of a fire?

A
  1. Ignition: Elements in suitable ratios
  2. Growth: Short stage, fire spreads (flashover)
  3. Fully Developed: Combustible materials ignited, hottest
  4. Decay: Decrease in oxygen or fuel (backdraft)
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15
Q

What is flashover?

A
  • During Growth stage
  • All combustible materials heated to their ignition temperatures
  • Simultaneous ignition, rapid fire spread.

It poses a severe risk during fire incidents.

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16
Q

What is backdraft?

A
  • During decay stage
  • Explosive event
  • Rapid re-introduction of oxygen to combustion in an oxygen-depleted environment.

This can occur when doors or windows are opened.

17
Q

How to find, recover, and identify accelerants?

A
  • Use sniffers/dogs
  • Identify the chemical nature of the accelerant
  • Collect fire debris
  • Extract and analyze samples using gas chromatography
18
Q

True or False: All compounds are molecules, but not all molecules are compounds.

19
Q

What is an accelerant?

A
  • Substances used to enhance the speed of fire spread
  • E.g. pentane, hexane, octane, and toluene.
20
Q

What are the two main types of chromatography?

A
  • Gas chromatography (Gas as mobile phase)
  • Liquid chromatography (Liquid as mobile phase)
21
Q

What is a chromatogram?

A
  • Record of separation in chromatographic system
  • Retention Time: Time for component to pass through the system
  • Peak area: Amount of component in the sample
22
Q

What does retention time indicate in chromatography?

A

The characteristic time for a component to pass through the chromatographic system

23
Q

How is the amount of a component in a sample determined?

A

By the peak area on the chromatogram

24
Q

What type of samples does gas chromatography analyze?

A
  • Volatile and thermally stable samples
  • Heated and vaporized as gaseous forms
  • e.g. gasoline, essential oils
25
Q

What type of samples does liquid chromatography analyze?

A
  • Nonvolatile and thermally unstable samples
  • In solution forms
  • e.g. drugs, poisons, pesticides, amino acids
26
Q

What is arson?

A

A fire started deliberately

27
Q

What is the purpose of comparing chromatograms in forensic analysis?

A

To identify the accelerant used to initiate a fire

28
Q

What is gas chromatography-mass spectroscopy (GC-MS)?

A

A technique that measures retention time and molecular weight of compounds

29
Q

What are the key issues in fire and arson investigation?

A
  • Point of origin
  • Cause of the fire
  • Evidence
30
Q

What is the role of a forensic analyst in fire investigations?

A

To analyze evidence and identify accelerants