A public health inspector investigates a case of methane gas accumulation and explosion in a municipal sewer. Methane is an example of which type of air pollutant, and which health hazard does high-concentration methane most directly cause?
- A Primary pollutant; direct pulmonary toxicity
- B Primary pollutant; asphyxiation by oxygen displacement ✓
- C Secondary pollutant; carcinogenesis
- D Secondary pollutant; photochemical smog
Correct answer: B. Primary pollutant; asphyxiation by oxygen displacement
Explanation
Methane (CH₄) is a primary air pollutant (emitted directly from the source). It is a simple asphyxiant — it is non-toxic in itself but displaces oxygen in an enclosed space, leading to hypoxia and asphyxiation when present in high concentrations. It is also a potent greenhouse gas and is highly flammable/explosive in concentrations of 5–15% in air, explaining sewer explosions. It does NOT have direct pulmonary toxicity.
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.