At about 6:20 a.m., on January 22, 1972, an overspeed tank car loaded with liquid petroleum gas collided with a standing hopper car in the Alton & Southern Railroad Company's Gateway Yard in East St. Louis, Ill. In the overspeed impact, an overriding coupler on the empty freight car punctured the tank head. The pressurized propylene gas in the tank car leaked to the ground and vaporized. A large vapor cloud was formed, which ignited and exploded. More than 230 people were injured as a result of the explosion, and property damage was estimated at more than $7 1/2 million.