The poster session will describe the applied methodology to the analysis of a series of explosions which occurred in the sewers of the city of Guadalajara, Mexico in April 1992.

It will show the systematic approach used to find the probable causes for the explosions, through the analysis of gas and liquids samples from the sewers and soil samples to determine the presence of flammable solvents.

Studies of the enormous damage originated from the explosions are shown, based on photographic evidence, and estimates of the required energy for the devastation were computed from material strength data, corrosion studies of the pipes involved and the probable volumes of fuels quantities.

It will present as well, a conclusion based in the development of a water lock in the sewers, originated by modifications made in the sewer system itself, and the accumulation of flammable solvents upstream of the lock in the sewer, which contributed to the explosions. As the explosion over-pressure decayed, the top section of the sewage lines, earth in the fill and road structures collapsed back into the sewers, resulting in the collapse of buildings around the affected streets. The conclusion was validated using an experimental model to simulate the phenomena.

The explosions caused structural damage in the above mentioned sewage, lifting the ground as well as the pavement on the streets along the system. The pipe collapsed, and the ground, pavement and everything on it went inside the pipe; the explosions impacted the land as an earthquake and with the collapse, they promoted the falling of buildings next to the streets along the system.

The hydrocarbon-air mixture in the sewage came from flammable liquids admitted on it. Some modifications to the system, mainly the blocking of the orient collector detouring the waters to the collector Rio San Juan to build a siphon at the crossing of line 2 with the city train system, caused the collector to be filled with water creating an hydraulic seal.

This seal promoted the accumulation of flammable liquid and vapors.

The analytical results available, known after the explosions, showed the presence of hexane and heptane, and some other compounds in less proportion in the sewage before the event. Those liquids might have promoted the explosions. Additionally, it was found that ten hours after the explosions, the poliduct of Pemex that was supplying fuels, was leaking in the Lazaro Cardenas Avenue. Gasoline Nova was admitted inside the same collector intermedio oriente.

Further findings showed damage to the poliduct caused by a water 3 inch piping laying on the poliduct. The cathodic protection on the poliduct, caused a corrosion in the water piping, by the pheno

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