Mexican Sewer Explosion

April 22, 1992

A Series of explosions in the Guadalajara, Mexico sewer system flattened buildings, hurled cars into air, and killed about a thousand people. Residents had been complaining of a strong gas-like odor and white smoke coming from the sewers for several days before the explosions. They were experiencing burning eyes, burning throats, and nausea. City workers found dangerously high levels of gasoline fumes. However, the city mayor did not feel it was necessary to evacuate the city because he felt that there was no risk of an explosion.
And investigation showed that new water pipes, made of zinc-coated iron, were built too close to an existing steel gasoline pipeline. The underground humidity caused these steel pipes to chemically react with the water pipes and corrode, creating a hole in the pipeline that permitted gasoline to leak into the ground and into the main sewer pipe. Normally, sewer pipes are built in a slope so that gravity helps move waste along. However, this sewer pipe had been recently rebuilt into a U-shape so that the city could expand its underground metro railway system. The city used an inverted siphon so that fluids could be pushed against gravity. However, while liquids were successfully pumped through, gases were not, and gas fumes built up, leading to the explosions.