Story by Kristen Cart
The dangers of storing grain have been well known for decades; however, history tends to repeat itself in spite of previous accidents and loss of life. When an operation falls into shoddy practices, and when safety measures are deemed too troublesome and expensive, the operation may continue for a time without incident. Eventually, the inevitable happens, and the investigators come in to discover why. The answers seem obvious in retrospect.
The explosion and fire at the gigantic DeBruce Grain facility near Wichita on June 8, 1998, was a perfect example of complacency and its consequences.
The elevator was built in 1954 by Chalmers and Borton of Hutchinson, Kan., for the Garvey Grain Company. It was a terminal elevator with arrays of tangential 30-foot-diameter bins, three abreast, with star shaped bins in the interstices. The bins were built 120 feet high and arranged symmetrically on either side of a 197-foot-tall, 21-story headhouse.
In 1955 the elevator was extended on either end, roughly doubling its capacity to nearly 21 million bushels. In total, 246 circular bins and an additional 164 interstice bins (for a total of 310) were available to store grain, in a structure that extended over half a mile. In its heyday it was the largest elevator in the world.
A key factor in the explosion of the facility was the arrangement of the runs atop the bins and the tunnels beneath. These communicated with all of the bins. A run extended in both directions from the headhouse, each containing a conveyor for distributing grain to the bins from the top using a tripper. Under each bank of bins on either side of the headhouse were two tunnels, each with a conveyor supplying the four headhouse legs. The pairs of tunnels on either side of the headhouse each had a connector tunnel between them.
All of the structure was interconnected in such a way that a fire or explosion could propagate throughout the elevator. And in fact, after the accident, that is what investigators found had happened.
For an explosion to begin, five factors must exist: fuel, oxidizer, containment, dispersion, and ignition. All of these factors are momentarily present in the controlled environment of a piston or turbine engine. In a grain elevator, the fuel is grain dust, the oxidizer is the oxygen in the air, the containment is the elevator structure, the dispersion is the suspension of dust in the air (stirred by operation of elevator components), and the ignition is the accidental trigger (a worn component, an electrical spark, or negligent smoking, for instance).
All these factors must be controlled to keep a grain elevator operation safe.
The DeBruce Grain elevator fire started with a seized bearing on an operating conveyor in one of the tunnels. The roller with the failed bearing stopped turning while the belt continued to run over it, causing excessive wear and heat. Dust grains in contact with the roller ignited. The fire touched off an explosive mix of suspended grain dust and air stirred up by conveyor operation. Very quickly, the entire elevator was involved in the disaster.
The concussion of the first explosion suspended more grain dust, causing a chain reaction. In a series of explosions, the fire propagated through that tunnel and through the crossover to the other tunnel on that side of the headhouse, running from end to end, then to the headhouse from below, and up and back into the run on top of the bins on that side, where it flamed out in an area that had been cleaned of dust. Only that run failed to explode. From the headhouse, the explosions propagated into the run, bins, and tunnels on the opposite side, until all of the explosive fuel was consumed.
The initial and follow-on blasts caused massive destruction. The headhouse sustained multiple explosions as the concussion reflected back in that direction at multiple points of entry. It was pulverized. Workers were trapped in the headhouse on floors above the worst of the destruction. On one side of the elevator, most of the bins blew their tops, utterly destroying the run above. The tunnels filled with grain that spilled from the bottoms of the wrecked bins, greatly complicating rescue and recovery efforts.
Seven employees and contractors died on the site–four in or near the tunnel adjacent to the ignition point, one in and one near the headhouse, and another blown clear of the elevator. Another ten were injured. Three of the hurt were trapped in the headhouse and another made his way out onto a bin roof. Some were outside of the elevator when they were injured by the blast.
A fascinating account of the rescue is included in the accident report. Eventually, a construction crane deposited rescuers and retrieved survivors. A helicopter from Fort Riley also plucked survivors from the top of the structure.
This was a textbook case of negligence, according to investigators. The dust was allowed to build up well beyond safe levels, and installed dust control systems were allowed to fill up and clog and become inoperable. Limited cleaning was done by employees by hand. The faulty bearing had ignited before, just days before the explosion, but it was not repaired.
The accident prompted interested parties to initiate an investigation, which was later sponsored by OSHA. The report is published on the OSHA site. The Grain Elevator Explosion Investigation Team (GEEIT) report is the source for the details presented here.
For those interested in learning more about the accident, an excellent article detailing the aftermath can be found at grainnet.com.