A forensic pathologist is calculating the approximate postmortem interval using Newton's law of cooling. The body temperature is 30°C, the ambient temperature is 20°C, and the normal living body temperature is assumed to be 37°C. Using the Henssge nomogram assumption, approximately how many hours have elapsed since death? (Approximate only — assume standard body weight and no modifying factors)

• A 2 hours
• B 7–9 hours ✓
• C 4–5 hours
• D 12–14 hours

Explanation

Applying the classical "Rule of Thumb": body loses approximately 1–1.5°C/hour under standard conditions. Temperature drop = 37 – 30 = 7°C; at 1°C/hour this gives approximately 7 hours. Adjusting for a 20°C ambient (warm environment — slower cooling) with a slightly lower rate suggests 7–9 hours. The Henssge nomogram refines this using body weight, ambient temperature, and body wrapping/insulation factors. The rule of thumb alone gives a reasonable PMI estimate of approximately 7–9 hours; choices A and B represent too short an interval, and D is too prolonged.

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.