• Coal miners face an increased risk of exposure to high methane gas concentrations.PhotoLink/Photodisc/Getty Images
  
  Methane gas is an odorless and colorless fuel, which creates heat and light. Septic systems, landfills and marshes are prime locations for methane gas to build up. Utility companies add odor to the gas, which creates a rotten egg smell to alert people in the area that the levels of methane may be too high. Exposure to methane gas usually occurs through inhalation. Methane evaporates quickly and does not contaminate food products or drinking water. It cannot pass easily into the body through the skin. Workers in sewers and people in areas with high concentrations are the most likely to be exposed.
  
  

Mild Methane Inhalation

• People who inhale methane may experience dizziness, fatigue and headaches. Methane gas displaces oxygen, which causes symptoms of asphyxiation. Methane levels kept below the explosion limit of 50,000 parts per million do not cause severe symptoms of oxygen deprivation.
  
  

Severe Methane Exposure

• When levels of methane are in high concentration above the explosion limit, oxygen deprivation can cause central nervous system problems such as rapid pulse, nausea and vomiting, loss of consciousness, convulsions and death. Note that these symptoms only occur when methane gas concentration is excessively high. Oxygen levels kept at 18 percent or higher do not result in severe symptoms. Mining operations pump oxygen into areas where methane gas is present to keep oxygen levels high and provide increased ventilation to avoid symptoms of oxygen deprivation.
  
  

Explosions

• Methane gas in high concentrations presents an explosion danger. Workers in mines and sewers must ensure that the work area has proper ventilation and oxygen levels are high to keep the concentration of methane gas at low levels. Methane gas is explosive at levels of five to 15 percent by volume. An explosion may occur when areas with high concentrations of methane gas encounter an ignition source such as a spark or flame. Coal miners are at an increased risk for methane gas explosions despite ventilation efforts when the geological conditions release unusually high levels of methane gas.