Which gas produced in landfills can be explosive when present at certain concentrations?

• A. Methane
• B. Oxygen
• C. Nitrogen
• D. Carbon dioxide

Answer: (A)

Methane is the gas produced by landfill decomposition that can be explosive when present in the right mix with air. It forms explosive mixtures in air over a roughly 5% to 15% concentration range; below that, it won’t ignite, and above that, it’s too rich to burn. In landfills, methane is a major hazard because it can accumulate in enclosed spaces if not properly collected and vented, so even a small spark can trigger an explosion. Other gases listed—oxygen, nitrogen, and carbon dioxide—do not form flammable or explosive mixtures in the same way: oxygen supports combustion but isn’t flammable itself, and nitrogen and carbon dioxide are inert and do not ignite.