Natural gas is both odorless and colorless, so Dominion adds an ingredient called mercaptan to it so you can detect its presence. If we did not add mercaptan, it would be hard for you to know that unlit natural gas was coming from your stove after you left the valve turned on. And leaks from furnaces and hot water heaters would be nearly impossible to detect without expensive equipment. So mercaptan's smell is a very valuable safety feature.
But one thing's clear -- mercaptan stinks. In a concentrated form, its smell is almost unbearable. And it takes only a few parts per million of mercaptan for the average person to wrinkle a nose and say, "What is that smell?"
Mercaptans contain sulfur. That's what makes them smell. The kind we use blends well with natural gas and, in a gaseous state, has much the same properties as natural gas, so it will also rise and dissipate with natural gas.
There are other uses for mercaptans in industry, including jet fuel, pharmaceuticals and livestock feed additives. They are used in many chemical plants. Mercaptans are less corrosive and less toxic than similar sulfur compounds found naturally in rotten eggs, onions, garlic, skunks, and of course, bad breath.