Natural gas has a chemical added that gives it a rotten egg odor. If you smell gas, shut off the source.nFor most of us, this is just the stovetop. Some decks have fireplace and deck propane. Take the gratesnoff the stovetop and lift off top. You should be able to reach the valve and close it. When gas is on, thenvalve will be parallel with the hose. Turn 45 degrees or perpendicular to shut off.