The New London Explosion: The Smell of SafetyHow a deadly oversight led to a now-universal warning.

From the show

Rules Written in Blood

That distinct 'rotten egg' smell associated with gas is not natural. It's an artificial safety measure with a tragic origin story. In 1937, a massive explosion destroyed a school in New London, Texas, killing nearly 300 people. The cause was a leak of odorless natural gas that had gone completely undetected. In the wake of the disaster, laws were passed requiring companies to add a powerful, foul-smelling chemical to natural gas, ensuring any future leak can be detected by scent.