Toxicology: phosgene exposure: 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 · Toxicology: phosgene exposure

Sample item

Workers exposed to a leaking industrial gas with the smell of newly mown hay seem well for several hours, and then develop breathlessness and frothy sputum. Which gas was involved?

APhosgeneBAmmoniaCHydrogen sulphideDCarbon monoxide

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

The answer and the reasoning

A. Phosgene

Phosgene has a faint smell of new-mown hay and causes little immediate irritation. After a latent period of hours it produces non-cardiogenic pulmonary oedema, so exposed workers must be observed. Ammonia gives immediate mucosal burning, hydrogen sulphide smells of rotten eggs, and carbon monoxide is odourless.

Option by option

A. Phosgene (correct)
Correct. A delayed pulmonary oedema after exposure to a hay-smelling gas is typical of phosgene.
B. Ammonia
Ammonia causes immediate burning of the eyes and airway.
C. Hydrogen sulphide
Hydrogen sulphide smells of rotten eggs and causes rapid collapse at high concentration.
D. Carbon monoxide
Carbon monoxide has no smell and causes headache and confusion.

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, Phosgene. Phosgene has a faint smell of new-mown hay and causes little immediate irritation.

Why is "Ammonia" not the answer?

Ammonia causes immediate burning of the eyes and airway.

Why is "Hydrogen sulphide" not the answer?

Hydrogen sulphide smells of rotten eggs and causes rapid collapse at high concentration.

Why is "Carbon monoxide" not the answer?

Carbon monoxide has no smell and causes headache and confusion.

What concept does this question test?

It tests Toxicology: phosgene exposure in Forensic Medicine. After a latent period of hours it produces non-cardiogenic pulmonary oedema, so exposed workers must be observed. Ammonia gives immediate mucosal burning, hydrogen sulphide smells of rotten eggs, and carbon monoxide is odourless.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Toxicology: phosgene exposure?

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.