Autopsy findings of antemortem (AM) burns

External findings

• Line of redness / hyperaemic zone at the margin of the burn, due to vital inflammatory reaction. It may be absent when death is immediate or when the whole body is extensively burnt.
• True blisters (vesicles/bullae):
  • Raised, tense, dome-shaped and contain fluid, sometimes gas.
  • Base is red, inflamed, moist and swollen, with oedematous papillae.
  • Blister fluid may contain protein and chloride, but this is not fully reliable alone.
• Inflammatory reaction in adjacent viable skin, demonstrated microscopically by vascular dilatation, congestion, oedema and leucocytic infiltration if survival was sufficient.
• If survival is prolonged: signs of healing such as granulation tissue, infection, epithelial regeneration and scar formation.

Internal findings indicating the victim was alive during the fire

• Soot deposits around mouth and nostrils, and more importantly in the larynx, trachea, bronchi and sometimes oesophagus/stomach, indicating active inhalation of smoke.
• Air passages are congested and may show mucosal inflammation, oedema and ulceration from hot smoke.
• Lungs may be congested and oedematous, with soot in bronchioles/alveoli.
• Carbon monoxide poisoning: blood, hypostasis and muscles may be bright cherry-red or pink due to carboxyhaemoglobin. Carboxyhaemoglobin estimation supports smoke inhalation, although its level can be altered by treatment and decomposition.
• General asphyxial signs may be present, including visceral congestion and pulmonary oedema.

Histochemical evidence of vitality

• Increased sulphydryl (SH) groups and acid mucopolysaccharides.
• Enzyme activity rises progressively with survival:
  • Esterases: about 1-2 hours
  • Aminopeptidases: about 2-4 hours
  • Acid phosphatase: about 4-6 hours
  • Alkaline phosphatase: about 8-12 hours

Important forensic point