Asphyxial deaths: gas in a disused well: practice question

A Forensic Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Forensic Medicine · Asphyxial deaths: gas in a disused well

Sample item

A worker is lowered into a disused well and collapses. A lighted candle lowered earlier was extinguished before reaching the bottom. Which gas is most likely responsible?

ACarbon dioxide, which is heavier than air, accumulates at the bottom and acts as a simple asphyxiantBMethane, which collects at the bottom because it is heavier than airCHydrogen sulphide, which is odourless and extinguishes flamesDCarbon monoxide, which extinguishes flames by displacing oxygen

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Carbon dioxide, which is heavier than air, accumulates at the bottom and acts as a simple asphyxiant

Carbon dioxide produced by decaying matter and fermentation is denser than air and settles in wells, pits and silos, displacing oxygen. A flame that goes out is the classic warning. Rescuers who enter without breathing apparatus often become further victims.

Option by option

A. Carbon dioxide, which is heavier than air, accumulates at the bottom and acts as a simple asphyxiant (correct)
Correct. The candle test and the heavy layer at the bottom point to carbon dioxide.
B. Methane, which collects at the bottom because it is heavier than air
Methane is lighter than air and collects at the top of enclosed spaces.
C. Hydrogen sulphide, which is odourless and extinguishes flames
Hydrogen sulphide smells of rotten eggs and is toxic rather than a flame-extinguishing asphyxiant.
D. Carbon monoxide, which extinguishes flames by displacing oxygen
Carbon monoxide burns and does not extinguish flames by displacement.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is A, Carbon dioxide, which is heavier than air, accumulates at the bottom and acts as a simple asphyxiant. Carbon dioxide produced by decaying matter and fermentation is denser than air and settles in wells, pits and silos, displacing oxygen.

Why is "Methane, which collects at the bottom because it is heavier than air" not the answer?

Methane is lighter than air and collects at the top of enclosed spaces.

Why is "Hydrogen sulphide, which is odourless and extinguishes flames" not the answer?

Hydrogen sulphide smells of rotten eggs and is toxic rather than a flame-extinguishing asphyxiant.

Why is "Carbon monoxide, which extinguishes flames by displacing oxygen" not the answer?

Carbon monoxide burns and does not extinguish flames by displacement.

What concept does this question test?

It tests Asphyxial deaths: gas in a disused well in Forensic Medicine. A flame that goes out is the classic warning. Rescuers who enter without breathing apparatus often become further victims.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Asphyxial deaths: gas in a disused well?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.