In electrocution, the finding of a Joule burn (electric mark) at the entry site is characterised by:

• A A deeply charred, blackened area with irregular margins covering most of the contact surface
• B A blister filled with serous fluid identical to a thermal burn
• C A petechial haemorrhagic area surrounding a central clear zone, identical to a stamp bruise
• D A pale, dry, depressed, yellowish-grey parchment-like area with a raised indurated rim, representing localised coagulation necrosis at the point of highest current density ✓

Explanation

The Joule (electrical entry) burn is pathognomonic of electrocution: it appears as a pale, firm, dry, parchment-like depression surrounded by a hyperaemic (red) raised rim — representing coagulation necrosis at the point where current density is maximal (contact site). Histologically, the skin shows elongated 'streaming' of nuclei in the sweat gland ducts. This is distinct from thermal burns (which blister and char) and from exit marks (which are larger and more irregular). The Joule burn's characteristic morphology allows identification of the contact point even in decomposed bodies.

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.