A municipal worker descends into an underground sewer manhole without ventilation and collapses within minutes. His colleague reports a rotten egg odour near the mouth of the manhole. The gas most likely responsible for the sudden collapse is:
- A Hydrogen sulphide ✓
- B Carbon dioxide
- C Methane
- D Carbon monoxide
Correct answer: A. Hydrogen sulphide
Explanation
Hydrogen sulphide, generated by decomposition of organic matter in sewers, has the classic rotten egg smell. At high concentration it paralyses the olfactory nerve so the smell disappears, and it directly depresses the respiratory centre, causing rapid collapse known as knockdown. Methane is odourless and acts only by displacing oxygen, and it does not produce this acute presentation.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.