Combustion and arson

Question 1

What are the four components of fire?

Answer 1

1. Fuel: Solid, liquid, or gas. Must vaporize for combustion.
2. Heat: Sufficient temperature to ignite fuel.
3. Oxygen: Found in the air; essential for combustion.
4. Chemical Chain Reaction: Maintains the burning process.

Question 2

What is the ignition temperature?

Answer 2

Ignition temperature is the minimum temperature needed to ignite a fuel spontaneously.

Question 3

What is the difference between flash point and pyrolysis?

Answer 3

• Flash Point: The temperature at which a liquid produces enough vapor to ignite.
• Pyrolysis: The decomposition of a solid into gaseous products to sustain combustion.

Question 4

What causes spontaneous combustion?

Answer 4

Spontaneous combustion occurs due to a natural heat-producing process in poorly ventilated areas.

Question 5

What are the common causes of accidental fires?

Answer 5

Accidental fires can be caused by faulty wiring, overheated electrical motors, poorly maintained heating systems, or cigarette smoking.

Question 6

How do accelerants influence fire?

Answer 6

Accelerants act as catalysts to enhance flammability, increase heat, and spread fire more rapidly. Common accelerants include gasoline, kerosene, diesel, and turpentine.

Question 7

How can accelerants be identified at a fire scene?

Answer 7

1. Physical Indicators: Burn patterns, unusual damage, or multiple origins.
2. Sniffers: Devices that detect volatile compounds.
3. Chemical Tests: Analyze residues using instruments like gas chromatographs.

Question 8

What steps should an investigator take to collect evidence at a fire scene?

Answer 8

1. Begin with the suspected point of origin.
2. Collect ash, soot, and porous materials likely to contain accelerants.
3. Use airtight containers with airspace to preserve samples.
4. Collect control samples of uncontaminated materials.
5. Search for ignition devices, such as matches or electronic devices.

Question 9

How should samples be stored?

Answer 9

Samples must be stored in airtight, break-resistant containers to prevent contamination and ensure integrity.

Question 10

What common sampling errors can occur?

Answer 10

• Insufficient sample collection.
• Collecting from the wrong locations.
• Failing to collect comparison samples.
• Ineffective preservation techniques.
• Breaking the chain of custody.

Question 11

What laboratory techniques are used to analyze fire debris?

Answer 11

Gas chromatography is the most sensitive method to detect and characterize flammable residues.

Question 12

What is the role of gas chromatograms in arson analysis?

Answer 12

Gas chromatograms separate hydrocarbon components, producing patterns that can identify specific petroleum products used as accelerants.

Question 13

What are some telltale signs of arson?

Answer 13

1. Multiple points of origin.
2. Use of streamers to spread fire.
3. Severe burn patterns on floors rather than ceilings.
4. Presence of accelerant residues.

Question 14

Why is finding the fire’s origin important?

Answer 14

Identifying the origin helps locate accelerants and ignition devices, determining whether the fire was intentional or accidental.

Question 15

What should an arson investigation report include?

Answer 15

1. Detailed descriptions of the fire scene.
2. Evidence collected and preservation methods.
3. Laboratory results of accelerant analysis.
4. Observations on burn patterns and fire behavior.
5. Conclusions regarding the fire’s cause and origin.

Question 16

What tools help detect accelerants in the field?

Answer 16

Portable gas chromatographs and sniffers are commonly used to detect volatile compounds at fire scenes.

Question 17

How does an investigator analyze ignition devices?

Answer 17

By examining recovered devices, such as matches, candles, or electronic igniters, to determine their role in starting the fire.

Question 18

What are some challenges in reconstructing a fire scene?

Answer 18

• Extensive damage obscuring critical evidence.
• Contaminants introduced during firefighting.
• Identifying accelerant residues in complex debris.

Question 19

What are some signs of accelerants at a fire scene?

Answer 19

• Multiple points of fire origin.
• Rapid fire spread.
• High heat stress and unusual burn patterns.
• Presence of chemical residues detected by sniffers or chromatographs.

Question 20

What types of evidence are collected at a fire scene?

Answer 20

1. Ash and soot from the suspected origin.
2. Porous materials like carpets and wood that might absorb accelerants.
3. Ignition devices such as matches or Molotov cocktails

Question 21

How should evidence be stored?

Answer 21

Evidence must be stored in airtight containers that prevent contamination and maintain integrity.

Question 22

What is the first step in analyzing fire debris?

Answer 22

The first step is extracting fire debris to obtain samples for instrumental analysis, typically using gas chromatography.

Question 23

How can burn patterns help determine fire origin?

Answer 23

Burn patterns can indicate points of intense heat, helping to identify the fire’s starting location and possible use of accelerants.