CRJ 248: Scientific Investigation Chapter 14: Arson and Explosive Evidence
Red Neck Smoke Alarm
Catching a Wildfire Arsonist
Potential Agencies at a Fire Scene Police Federal B.A.T.F.E. Ambulance Fire State Fire Marshal Insurance Investigators Gas/Electric Utilities
Arson: Willful and malicious burning. Some Motives Profit Revenge Vandalism Crime Concealment Excitement Terrorism
Fire Tetrahedron
Fire Components Terminology Flashpoint Lowest temp. at which a material will burn under lab conditions. Capable of burning with a flame. Flammable Flame Point Temp. needed to sustain continuous flame. Combustible Fuel Capable of burning in air, under normal conditions. Gas, liquid, or solid at ambient temperature.
How is Heat Transferred? Conduction Convection Radiation
Four Classifications of Fires Wood, cloth, paper, plastics Liquids, greases, gases Class A Class B Energized electrical equipment Class C Class D Combustible metals like sodium, potassium
Combustion Products of Fire Heat Gases Flame Smoke
Stages of Fire Development: Incipient (Growth) Stage Begins at the moment of ignition. Flames are originally localized. Gases rise and begin to accumulate. Upward and outward fire spread.
Free-Burning Stage More fuel is consumed, fire intensifies. A hot, dense layer of smoke and fire gases is collecting near ceiling. Heat begins to radiate downward. Gases begin to spread throughout the entire building. Rollover occurs when the upper layers ignite. May lead to secondary fires starting.
Flash-Over Upper layer reaches approximately 1,100 F. All fuels in the room simultaneously ignite. Temperatures rise to over 1,000 F at the floor level and 2,000 F at the ceiling. The flashover stage may be reached in as little as 2 or 3 minutes.
After Fire is Out Notice V pattern and coloration difference in area where fire started.
Legal Aspects of Fire Investigation Has authority to investigate. Exigent circumstances, no need for search warrant. Fire Department Later, can get an administrative warrant, without showing probable cause. Can remain on scene for reasonable amount of time to investigate.
Two Important Concepts in Fire Investigations Area of Origin Large area where fire might have started. Work from area of least, to most destruction. Point of Origin Location where fire actually started. Multiple points could exist.
Fire Development Most Damage? V pattern Lowest Fire
Structure still intact
Possible Sources to be Ruled Out Kitchen stove: Knobs shut off? Yes. Furnace charred? No. Space heater in living room (not in area of most damage). Wood-burning stove in living room (not in area of most damage). Space heater in bedroom (not area of most damage). Water heater in hallway. Occupant smoking, or candle use (none found).
Area of Lowest Burning
Fire Direction, Area of Lowest Burning, Area of Deepest Charring
The Cause
Does This Make Sense to You? Wood burning Stove Water Heater
Fire Cause Classifications Act of God, lightning Unintentional, can be explained. Natural Accidental Incendiary Undetermined Intentional, criminal Cause unknown
Physical Examination of the Fire Scene Analyze Data (Reason) Test Hypothesis (Makes Sense?) Define Problem (Classify Cause) Collect Data (Investigate) Fire Scene
Fire Scene Examination How did firefighting efforts change scene? Ask them about fire location/condition. Did they see anything unusual? Document flame/smoke colors. Conduct interviews of witnesses. Interior examination for burn patterns. Note location/condition of doors/windows. Photograph crowd of onlookers. Insure structural integrity before entering scene.
Smoke Colors
Heat Distension of Light Bulbs
Burn Patterns Burn patterns will generally lead to the point of most severe damage which contains the point of origin. An exception occurs when a flammable material trail is used. The most common pattern is the V or conical pattern (burns up and out).
V Pattern: Exterior View
V Pattern: Interior View
Electrical Fire Caused by Overloaded Plug
Alligator Charring Patterns
Inverted Cone Pattern Triangular Pattern
Accelerant Pour/Trailer Patterns
Normal Fire Paths
Typical Fire Development
Scene Documentation Photos Inventory of Contents Collection of Physical Evidence 99.9 % of the time, the one who stood to gain the most from the fire is the one who set it.
Items Used to Collect Physical Arson Evidence Catalytic Combustion Sensor Layering: Evidence should be examined, and collected in layers. Each layer should be separated.
Explosives Investigations: Types of Explosives Low Explosives: Detonation Speed Less Than 3,300 ft./sec. Low Explosives Detonation Speed Less Than 3,300 ft./sec. High Explosives Detonation Speed Greater Than 3,300 ft./sec. Pyrotechnics Black/Smokeless Powder TNT
Two Types of Investigations Pre- Detonation Threats Suspicious Items Post- Detonation Aid the injured Watch for secondary device
Vapor from a liquid in a confined space will expand when heated until it explodes.
International Association of Bomb Technicians and Investigators