Sugar Refinery Wastewater Treatment Facility Explosion

A sugar refinery wastewater treatment plant under construction suffered an explosion during the construction of two aeration tanks.  Without warning, an explosion occurred in the sump from which wastewater was being pumped into the operating tank.  A second explosion a few seconds later caused major damage to the first aeration tank, then in operation, while the second was still under construction.  Rimkus was retained to determine the cause of the explosion. more...

The city had required the construction of the wastewater treatment facility to treat the stream prior to its delivery into the sanitary sewer system because the make-up of the stream was overwhelming the city’s facilities.  The plan called for two tanks with aerators to treat the wastewater.  The wastewater first flowed into a sump from which a submersible pump pumped it into the top of the tank.  From the tank, the now treated wastewater would exit through a standpipe and flow to the sewer.  The sump also had a bypass line through which the wastewater could flow directly into the sewer in an emergency situation (such as a pump failure).

Within the first 30 minutes following our arrival at the site, we had determined the cause of the first explosion and the sequence of events leading to the second, more damaging explosion.  We determined that (1) the submersible pump, originally explosion-proof, was no longer such; (2) the piping from the tank standpipe connected with the sump overflow pipe below ground at some point prior to reaching the sewer; and (3) the initial sump explosion caused a flame front that traveled down the bypass line, back up the outlet pipe to the standpipe, and into the top of the operating tank—which was full of explosive gasses from the breakdown of the sugars in the wastewater.  Subsequent tear-down of the sump pump, along with review of the underground piping plan for the treating plant under construction, proved out our theories.