Safety in sewer manholes: If a miner’s safety lamp flame extinguishes within about 5 minutes in a manhole, which gas (or condition) is most strongly indicated?

Introduction / Context:
Confined space entry into sewers is hazardous because toxic and asphyxiating gases may accumulate. Historically, miner’s safety lamps were used as crude indicators. Understanding which gas condition extinguishes a flame helps reinforce gas-monitoring protocols before entry.

Given Data / Assumptions:

• A sewer manhole with poor ventilation.
• Flame extinguishes within minutes after lowering.
• No modern multi-gas meter is assumed in this scenario (for learning purposes only).

Concept / Approach:
Flames need sufficient oxygen; excess carbon dioxide displaces oxygen and does not support combustion, so flames go out. Methane is combustible and would not extinguish a flame by itself (it may ignite with oxygen present). Hydrogen sulphide is toxic and flammable, but low O2/high CO2 is the classic reason for flame extinction without ignition. Thus, rapid extinction signals high CO2 (and/or low O2).

Step-by-Step Solution:
Observation: Lamp extinguishes quickly without explosion.Inference: Atmosphere is oxygen-deficient, commonly due to elevated CO2.Select CO2 as the indicator gas associated with flame extinction.

Verification / Alternative check:
Modern practice requires calibrated multi-gas meters (O2, H2S, CH4, CO, etc.) and ventilation. The historical lamp observation aligns with oxygen displacement by CO2.

Why Other Options Are Wrong:
H2S: Highly toxic; may burn with a blue flame—does not inherently snuff flame without oxygen depletion.CH4: Explosive risk; in the right range it may ignite rather than extinguish a flame.O2 enrichment: Would enhance, not extinguish, a flame.None of these: Incorrect because CO2 is a known cause.

Common Pitfalls:

• Assuming any dangerous gas will extinguish a flame; only oxygen-deficient or CO2-rich atmospheres do.
• Relying on flames instead of proper gas detection for real-world safety.

Final Answer:
Carbon dioxide (CO2)