Natural gas heats about half the homes in the United States and runs the stoves in most of them. It is safe enough that we pipe it under every street. It is also the fuel behind some of the most destructive residential explosions firefighters ever respond to.
Natural gas is highly flammable. It is mostly methane, which ignites in air at concentrations between about 5% and 15%. Below 5% there isn't enough fuel; above 15% there isn't enough oxygen. Inside that window, any ignition source will do: a furnace pilot, a doorbell, a refrigerator compressor kicking on, a cell phone. Its autoignition temperature is around 1,000°F, but a spark is all it takes.
Natural Gas vs. Propane
The key difference is that natural gas is lighter than air. It rises. A leak in a house collects at the ceiling, in the attic, and in upper rooms, and given ventilation it will disperse outdoors. Propane does the opposite and pools low, which is why the two fuels produce different kinds of emergencies. We cover the propane side in is propane flammable.
Natural gas is odorless on its own. Utilities add mercaptan, the rotten egg smell, so leaks can be detected by nose. If you can smell it, there is enough gas present to matter.
How Gas Explosions Happen
A gas explosion needs three things: a leak, an enclosed space where the gas can reach the flammable range, and an ignition source. In a house, all three are easy to get. The leak comes from a failed appliance connector, a cracked line, a stove knob bumped on, or an excavation strike on the service line outside. The enclosed space is the house. The ignition source is whatever turns on next.
What makes these calls so dangerous is that the gas can migrate. It travels through wall cavities, along sewer lines, and into neighboring buildings. Firefighters have responded to explosions in a house that had no gas service because the leak was next door.
If You Smell Gas
- Don't flip any switches, on or off. Don't use the phone inside. Don't start the car in an attached garage.
- Leave immediately and take everyone with you. Leave the door open on your way out.
- Call 911 and the gas company from outside, at a safe distance.
- If the smell is faint and clearly coming from a stove knob that got bumped, turn the knob off and open windows. If it is strong, or you can't find the source, get out.
- Don't go back in until the fire department or utility has cleared it.
Signs of a Gas Leak Besides the Smell
- A hissing sound near a gas line or appliance
- Dead or dying vegetation over a buried line in an otherwise healthy yard
- Bubbling in standing water or a puddle that won't freeze in winter
- Unexplained headaches, dizziness, or nausea that clear up when you leave the house
- Pilot lights that keep going out, or a stove flame that burns orange instead of blue
Preventing Gas Leaks at Home
- Have your furnace and water heater serviced annually.
- Replace old flexible appliance connectors, especially uncoated brass ones from before the 1980s.
- Install a natural gas detector near gas appliances and in the utility room. They are inexpensive and separate from carbon monoxide detectors.
- Call 811 before you dig, every time.
- Use child locks or knob covers on gas stoves if you have small kids.
Our article on whether the fire department will check for gas leaks answers the follow up question most people have. The short version: yes, call us. We would much rather check a smell than respond to what comes after.
