The things you overhear in work.

Are you sitting comfortably? Then I'll begin. Today's lesson concerns Mercaptan.
Natural gas normally is non-toxic, tasteless, colorless and odorless. A scent known as mercaptan, is added to the gas to make it 'smellable'.
Mercaptan is an acrid chemical, that can be recognised immediately, should there ever be a leak. Mercaptan makes natural gas smell like sulphur, or rotten eggs.