Lesson 4
Fire Investigation
In This Lesson
1. Investigation Process
Fire investigation is a systematic process to determine the origin, cause, and responsibility for a fire.
Steps in Fire Investigation
- 1
Secure and Protect the Scene
Establish perimeter, prevent contamination, control access
- 2
Document the Scene
Photographs, video, sketches, written notes
- 3
Determine Point of Origin
Locate where fire started using patterns and physical evidence
- 4
Identify Fire Patterns
V-patterns, char depth, heat shadows, smoke staining
- 5
Collect and Preserve Evidence
Physical evidence, samples, accelerant residue
- 6
Interview Witnesses
First responders, occupants, neighbors, building owners
- 7
Determine Cause and Responsibility
Classify as accidental, natural, incendiary, or undetermined
Scientific Method in Fire Investigation
- Recognize the need (fire occurred)
- Define the problem (what caused it)
- Collect data (evidence, interviews)
- Analyze data (patterns, timing)
- Develop hypothesis (possible cause)
- Test hypothesis (eliminate alternatives)
- Select final hypothesis (determine cause)
2. Point of Origin
The point of origin is the specific location where the fire began. Determining this is crucial to identifying the cause.
Indicators of Origin
Physical Indicators:
- • Deepest charring
- • Most severe damage
- • Lowest burn patterns
- • V-pattern apex
Witness Information:
- • First flames observed
- • Smoke color/direction
- • Sounds (explosions)
- • Activities before fire
Area of Origin vs Point of Origin
Area of Origin
General location where fire started (room, floor, section)
Point of Origin
Specific location within the area (outlet, appliance, spot)
3. Fire Patterns
Fire patterns are visible marks left by fire that help investigators trace fire movement and determine origin.
V-Pattern
Most common fire pattern. Fire burns upward and outward from origin, creating a "V" shape on walls.
- • Apex: Points toward origin
- • Narrow V: Fast-burning fuel or accelerant
- • Wide V: Slow-burning or smoldering fire
Char Patterns
Carbonized wood surface indicating fire intensity and duration.
- • Deep charring: Indicates longer burn time or higher heat
- • Alligatoring: Large shiny blisters (rapid intense fire)
- • Small alligatoring: Long, slow burning
Other Patterns
Smoke Staining
Soot deposits indicating smoke flow
Heat Shadow
Protected area behind object (clean spot)
Pour Patterns
Irregular patterns from liquid accelerants
Trailer
Path connecting multiple fire origins
4. Fire Causes
Fire causes are classified into four categories based on how the fire started.
Accidental
Fire caused by unintentional human action or equipment failure.
- • Electrical malfunction
- • Cooking accidents
- • Smoking materials
- • Heating equipment failure
- • Children playing with fire
Natural
Fire caused by natural phenomena without human involvement.
- • Lightning strike
- • Spontaneous combustion
- • Volcanic activity
- • Earthquake damage
Incendiary (Arson)
Fire deliberately set with intent to cause damage.
- • Use of accelerants
- • Multiple points of origin
- • Incendiary devices
- • Evidence of forced entry
Undetermined
Cause cannot be determined with reasonable certainty.
- • Insufficient evidence
- • Scene too damaged
- • Multiple possible causes
- • Evidence contaminated
Common Electrical Fire Causes
5. Arson Investigation
Arson is the willful and malicious burning of property. Special investigative techniques are required.
Indicators of Arson
Physical Indicators:
- • Multiple points of origin
- • Pour patterns (accelerants)
- • Trailers connecting origins
- • Unusual burn patterns
- • Incendiary devices
Circumstantial Indicators:
- • Disabled fire protection
- • Missing valuables
- • Signs of forced entry
- • Recent insurance increase
- • Financial problems of owner
Common Arson Motives
Profit
- • Insurance fraud
- • Eliminate competition
- • Urban renewal
Concealment
- • Hide other crimes
- • Destroy evidence
- • Obscure murder
Revenge
- • Personal grudge
- • Domestic dispute
- • Labor dispute
Evidence Collection
- •Accelerant samples: Collect in clean, airtight containers (glass or metal cans)
- •Comparison samples: Unburned material from same location
- •Incendiary devices: Document, photograph, carefully collect
- •Chain of custody: Maintain documented transfer of evidence
BFP Fire Investigation Tips
- ✓Know the investigation steps - systematic process from securing scene to determining cause.
- ✓Understand fire patterns - V-patterns, char depth, pour patterns.
- ✓Learn cause classifications - accidental, natural, incendiary, undetermined.
- ✓Recognize arson indicators - multiple origins, accelerants, motives.