Anatomy of a Waste Water Tank Explosion

In Anatomy of a Waste Water Tank Explosion, you'll learn ...

• How a single source of ignition can set off a series of explosions
• Why recording the sequence of events is important in an explosion investigation
• How construction drawings and process flow diagrams and the skill to read them, can sometimes be essential to figuring out a fire propagation path
• How a simple difference in piping configuration could have prevented the tank explosion that occurred in this account

Overview

Credit: 1 PDH

Length: 24 pages

This course will present a detailed anatomy of a waste water tank explosion. It was a new tank, not even finished in its construction. The tank was a large aboveground tank in which process waste water was to be aerated. The purpose of the aeration was to strip out volatile gases dissolved in the water. The tank explosion was actually the last in a series of four explosions. This all happened in the late 1990's at a sugar refinery.

At that time, expansion of the refinery's process waste water treatment facility was underway. Although construction was still going on, some of the new equipment was already in use. For example, process waste water was flowing into a new underground sump. A rented submersible pump was being used to pump the waste water up out of the sump and into the new aeration tank. However, at that time the aeration equipment had not yet been commissioned. Consequently, the would-be aeration tank was temporarily being used as merely a holding tank. The waste water flowed out of the tank by gravity through an outlet standpipe located inside the tank, like in a toilet tank. The water flowed into the open top of the standpipe and down its interior walls to join the underground sump overflow pipe, which flowed into the city storm sewer system.

At about 4:30pm one afternoon, an explosion in the sump blew the sump cover off. Eyewitnesses next heard rumbling and felt ground vibrations, and they saw pipes shaking. Then the roof of the tank ballooned, and the tank wall partially collapsed into a scalloped pattern around the circumference of the tank, at the seam between the tank wall and the tank roof.

This course reviews how three engineers figured out the cause of the explosions. The course explains how they performed a site inspection, discussions were held with refinery staff and each other, and observations and hypotheses were systematically made. The course tells how data was collected, a pump disassembly and inspection were performed, and all the information analyzed in a scientific manner, in order to determine the cause and origin of these explosions. They also determined how such an explosion can be prevented in the future.