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Elevator Description -- Reported in Guinness Book of Records as the world's largest grain elevator, the DeBruce Grain elevator was located approximately 4 miles southwest of Wichita, Kansas. Its storage capacity was 20.7 million bushels. Were the elevator to store wheat exclusively, it could have supplied the wheat for all the bread consumed in the United States for nearly six weeks.
The elevator was laid out in a northeast/southwest direction, but for purposes of easy reference, it was generally described as though it was oriented north/south. Figure 2-1 is an aerial view taken of the east side of the DeBruce elevator within an hour after the explosion.
Aerial View of DeBruce Grain elevator
The elevator complex at the time of the explosion consisted of 246 circular grain silos (often also referred to as tanks or bins) that were 30' in diameter and 120' in height, arranged in a linear array of 3 silos abreast. The 164 star-shaped spaces between the circular silos were also used for grain storage and are known as interstice silos. There were therefore a total of 310 grain storage silos in the elevator.
Located midway between these 310 grain storage silos -- and separating them into a north array and a south array -- was a headhouse 216.5 feet high from its basement floor, standing 197 feet above ground. It was 42' square in cross-section and housed four elevator legs as well as facilities to weigh and distribute grain into selected silos. The overall length of the elevator -- headhouse and silos -- was 2,717 feet, well over one-half mile long.
Across the top of all these 310 silos were two 1,300' galleries, approximately 46' wide and 10' high -- one for the south silo array and the other for the north. Elevated grain was carried horizontally in each gallery by belt from the headhouse out to a selected silo and then dumped into that silo, using a "tripper" to divert the grain from the belt.
Location of Victims -- Those who were killed or injured were located at the time of the explosion as described:
Within west tunnel, south array: Four fatal
Fatalities -- A total of seven men were fatally injured in the explosion. They were employees of either DeBruce Grain or Labor Source Incorporated (LSI).
Injured-- The ten men who were injured in the explosion were employees of four companies: DeBruce Grain, Labor Source Incorporated (LSI), Dusenbery Trucking, and Rob Heimerman Trucking.
On-Site Uninjured -- There were ten people -- present on DeBruce property adjoining the elevator -- who survived the explosion. They were employees of four different companies. Most of them played roles in immediate search-and-rescue efforts. Their testimony was helpful and contributed to the GEEIT investigation.
Physical Damage -- Beginning in the east tunnel of the south array of silos, a series of explosions -- utilizing a crossover tunnel -- were propagated both directions in the two tunnels of the south array. Upon reaching the headhouse via both south tunnels, blast and fire blew upward through the headhouse, and into the south gallery from the headhouse for only a short distance. Because grain dust in that gallery near the headhouse had just been cleaned, the blastwave separated from the trailing fireball causing the latter to self-extinguish. However, although most of the south gallery thereon south remained integral, there was more than ample grain dust available -- had there been an ignition source -- to have destroyed the remainder of the south gallery.
However, that same blast wave and fire also moved out from the headhouse into the north gallery where it continued while also diverting downward through empty silos into the west north tunnel where it was diverted both south back into the headhouse basement and north to the exit, passing the cross tunnel where it propagated to the east north tunnel and where it went both north to the exit, and south to the headhouse.
As blast waves passed northbound beneath silos in both the north array tunnels, they rose vertically through those silos to the north gallery (most of which was destroyed) and blew off many silo tops as shown in Figure 2-2. In addition, numerous silos in both south and north arrays -- particularly those which were empty -- were destroyed by blast and fire. The 21-story headhouse -- shattered from bottom to top -- had to be torn down without being as thoroughly accessed and investigated by GEEIT for additional clues of blast direction and propagation within it as was desired.
Aerial View of North Gallery, DeBruce Grain Elevator
Most of the silo sheet-metal discharge spouts -- known as blast gates -- that release grain onto tunnel belts were either blown away or disabled so that all four tunnels were nearly choked with spilled grain. The force of successive explosions was sufficient to pulverize much of the structural concrete rather than simply break it into large chunks as usually occurs in grain elevator explosions of lesser severity. This effect was greatest at the north end of the elevator because of the large L / D (gun barrel) effect.
Rescue Factors -- Lack of worker knowledge of a DeBruce Grain Emergency Action Plan (because it existed only on paper and had neither been described to nor rehearsed with workers) -- coupled with absence of documented work assignments for all personnel (DeBruce Grain as well as independent contractors and trucking firms) working in the elevator at the time -- precluded early accountability for the number of affected personnel as well as their possible location within the elevator property.
Though local fire and rescue response was on-scene within 10 minutes after the explosion, considerable delay in implementing their efforts occurred due to identifying both the number of affected people and where they might be found within the vast, badly damaged, and burning conglomerate. In addition, there were widely-expressed but erroneous beliefs that additional explosions were to be expected. So great caution occurred -- even in rescuing and treating badly injured survivors in and near the elevator.
The immensity of the elevator structure (height, length, and limited access) presented rescuers and those performing triage with great challenges. The most severely injured had to be lifted from the top of 120' silos where they had either managed to escape on their own or where they had been assisted by rescue crews. A local company immediately sent its large crane to assist in lifting victims from the top of the elevator silos. A US Army helicopter flew 120 miles from Fort Riley, Kansas to the scene to lift an injured worker from the elevator gallery roof. After about four hours, all survivors within the elevator had been lifted by either crane or helicopter.
President Clinton declared Sedgwick County, in which the elevator was located, a federal emergency the day after the explosion. This designation released the Federal Emergency Management Agency (FEMA) to dispatch 20 trained searchers to the scene along with 42 support personnel.
Because one victim's body was not located for weeks following the explosion, rescue activities were prolonged for five weeks before gradually being converted into recovery operations -- whereupon FEMA's Urban Search and Rescue team of over 60 personnel departed for their home base in Lincoln, Nebraska.
Probable Causation -- No grain elevator explosion has a singular cause. As elaborated in Chapter 7, there are five components of every such explosion -- often described as the Explosion Pentagon: fuel (powdered grain), oxidizer (air), fuel-and-oxidizer containment within a closed volume (elevator), dispersion of fuel-and-oxidizer mixture within the limits of explosivity, and ignition. Without any question, all five of those factors happened simultaneously on 8 June 1998.
The initial DeBruce Grain elevator explosion -- which set off a series of additional explosions of increasing severity -- occurred when grain dust was ignited in the east tunnel of the south array of silos. The most probable ignition source was created when a concentrator roller bearing, which had seized due to no lubrication, caused the roller to lock into a static position as the conveyor belt continued to roll over it. This “razor strop” effect on the roller raised its temperature to 260oC, well beyond the 220oC required to ignite layered grain dust which was plentiful inside the roller.
Because the belt was running in that tunnel at the moment of explosion it was creating a convective airflow. Witnesses reported that during elevator operation that the cloud of suspended grain dust was often so thick that during these times one could not see their hand in front of their face. The dispersion of the smoldering dust contained within the conveyer roller and its impact upon the floor dust layer, which would raise additional dust to also be dispersed by the convective flow would produce an ample fuel oxidizer mixture to be ignited by the glowing embers.
But it would be an error to focus on the details of likely ignition as the reason the elevator was destroyed. Of far greater consequence in causing the explosion -- and the key to preventing a similar one in the future (which should be the primary purpose for investigating any accident) -- are the deliberate DeBruce corporate decisions to (a) allow massive amounts of fuel to continually be created and distributed throughout the elevator -- awaiting any one of many possible sources of ignition, (b) forego repair and restoration of long-failed grain dust control systems, and (c) abandon preventive maintenance of elevator equipment -- particularly the grain conveyor and grain dust control systems. These three factors -- voluntarily exercised by DeBruce in opposition to widely-known and recognized methodology for explosion prevention -- caused the catastrophe. All three, which were well within DeBruce cognizance and control, made the disaster an inevitability.