As the manufacturer of natural gas odorizers, visitors frequently ask, “What is the chemical added to natural gas to make it smell?”
In “What is Natural Gas Odorization?” we mention that natural gas by itself is odorless. Because it is combustible, an odorant is injected into the gas at a federally regulated level so that an individual with an ordinary sense of smell can sense it.
Most odorants are a mixture of various compounds, a popular constituent being mercaptan.
What is Mercaptan?
Mercaptans are colorless flammable gases with an unpleasant odor often described as rotting cabbage or rotten eggs. Mixtures of sulfides and mercaptans are common odorants. When you smell it, you want to leave. That is the intention for a gas odorant, to alert people that flammable gas is present and do something, like vacate the area or potentially troubleshoot.
Mercaptans are also used as an intermediate in the production of jet fuels, pesticides, and plastic, along with methionine synthesis. Methionine is an amino acid and used as a supplement for poultry and other animal foods.
A mercaptan material safety data sheet typically lists it as a “colorless gas with an extremely unpleasant odor.” At very high concentrations, mercaptans are toxic and affect the central nervous system. The penetrating odor associated with mercaptans is detectable well below dangerous levels. The gas has a smell at an odor threshold of 1 ppb, and OSHA has a Permissible Exposure Limit for mercaptan of 10 ppm.
See more in the FAQ in About Gas Odorization.
More on Odorant