Fire Scene Investigation Lecture

Overview

• Current research being reviewed; past theories debunked.
• Importance of understanding normal vs abnormal electrical activity.
• No absolutes in electrical system damage; "I don't know" is an acceptable conclusion.

Terminology

• Arc: Discharge from electrical fault or switch operation.
• Arc site: Location of damage by an arc.
• Bead: Rounded globule of re-solidified metal; misunderstanding in definition leads to incorrect assumptions.
• Arc melting: New definition proposal to capture all arcing characteristics.

Characteristics of Arc Damage

• Abnormal electrical activity produces characteristic damage.
• Key characteristics include mass loss, mass transfer, and re-solidification waves.
• Fire cannot precisely cause arc-like damage; look for sharp lines of demarcation.

Lab Test Observations

• Arc melting looks similar across different regions (e.g., Japan and USA).
• Important indicators: localized damage, bead formation, spatter indicating molten state.
• Longitudinal lines on copper indicate lack of melting by fire.

Fire vs Electrical Damage

• Fire damage: slow, gravity-affected, no sharp lines.
• Electrical damage: fast, localized, sharp demarcation.
• Arc mapping considered unreliable as a fire pattern alone.

Factors Influencing Arc Damage

• Length of circuit, conductor size, system voltage, and fault resistance affect damage.
• Distinction between long-duration (more mass loss) and short-duration (less mass loss) arcs.

Practical Application

• Building construction affects arc observation and interpretation.
• Artifacts like beads must be analyzed in context; not sole indicators of fire cause.
• Understanding wiring in conduit crucial for reliable analysis.

Conclusions

• Reliable identification requires practice.
• Multiple characteristics help in determining nature of damage.
• Training and experience critical in fire scene investigations.