Glass fracture analysis at a crime scene reveals both radial fractures (extending outward from the impact point) and concentric fractures (rings around the point of impact). In assessing direction of force and sequence of shots in multiple impacts, which principle is applied?

• A Radial fractures form first, and concentric fractures stop when they reach existing radial fractures ✓
• B Concentric fractures form first, and radial fractures stop at pre-existing concentric fractures
• C Both fracture types form simultaneously and cannot be sequenced
• D Radial fractures indicate pulling force; concentric fractures indicate pushing force

Explanation

In glass fracture mechanics, radial fractures form first (radiating outward from the point of impact during the loading phase) and concentric fractures form later (as the glass bends back). For sequencing multiple impacts, the key principle is that fracture lines terminate when they meet pre-existing fractures. Therefore, radial fractures from a second impact will stop when they reach radial or concentric fractures from the first impact, allowing forensic reconstruction of the sequence of shots. The ARCDE rule (Analyze Radial Cracks to Determine Entry/exit direction) uses the 4R rule: Radial fractures form first on the Reverse side (exit/tension side) of the force.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.