Methane

Natural gas and oil production, landfills, livestock, wetlands, coal mines, wastewater/sewers, and leaks from pipelines or gas appliances (an odor is added to utility gas) [1][3].

Breathing air near leaks, landfills, sewers, or in confined/poorly ventilated spaces; outdoor levels are usually low and disperse quickly [1][2].

High concentrations reduce oxygen (headache, dizziness, unconsciousness, suffocation) and pose fire/explosion hazards; methane also contributes to climate change and to ozone that worsens lung and heart problems [1][2][3].

Oil and gas, mining, wastewater, agriculture, and landfill workers; people in homes with gas appliances or near leaks; anyone in confined spaces; those with asthma/heart disease during high-ozone days [2][3].

Fix suspected gas leaks, maintain and ventilate gas appliances, and leave immediately if you smell “rotten egg” odor—then call your utility from a safe place; workers should monitor air and follow confined-space and ignition-control rules [1][2].