<P> An odorizer is a device that adds an odorant to a gas . The most common type is one that adds a mercaptan liquid into natural gas distribution systems so that leaks can be readily detected . Other types have been used for carbon dioxide fire extinguishers . </P> <P> A major spur to the development of gas odorants and odorizers was the March 18, 1937 natural gas leak that blew up a school in New London, Texas, killing 294 children and teachers . </P> <P> Natural gas odorizers run the gamut from a simple wick in a container to computerized equipment, which controls the amount of odorant based on flow rate, tracks the amount of odorant in inventory, and alarms when odorant is not being injected into the gas stream . </P>

When did they start adding odor to natural gas