Natural gas is the most widely used source of energy for household heating and cooking, and for the most part it's quite safe. However, homeowners need to be vigilant about the risk of natural gas leaks. Every year, people die because of undetected or unrecognized gas leaks. The most common cause of death is asphyxiation, but sometimes a gas-filled basement will explode into a fireball that quickly consumes the entire house.
Though natural gas, or methane, isn’t poisonous, it displaces the levels of oxygen we need to breathe. At sea level, the atmosphere contains 21 percent oxygen, and you need at least an 18 percent concentration to breathe normally. As the methane displaces the oxygen in an enclosed space, you’ll start to get dizzy and disoriented, lose concentration and coordination. As oxygen levels continue to decrease, you’ll feel tired, even exhausted. Your heart rate and breathing will increase. Eventually, you’ll feel nauseated, lose consciousness and stop breathing.
Methane gas is highly combustible, with a small amount producing lots of heat. But it requires just the right mixture with oxygen to cause an explosion in an enclosed space. Less than 5 percent of natural gas in the air isn’t enough to ignite, and more than 15 percent doesn’t have enough oxygen, according to experts interviewed by the Indianapolis Star. So for an average home, at least 10 percent of the gas needs to permeate the air before it can combust.
Also keep in mind that some leaks may start in your basement, which means that if you start to smell gas on the second floor, a large amount may have already accumulated downstairs.