Intro | DeBruce Grain Elevator Explosion - Report
The most significant chapters from the report on the explosion of the DeBruce Grain Elevator that occurred June 8, 1998 Wichita, KS are featured here. This report was submitted by the Grain Elevator Explosion Investigation Team (GEEIT) and explains the investigation and cause of the explosion that killed 7 and injured 10 employees.
Chapter 1 | Engagement of Investigatory Expertise
Grain Elevator Explosion History
Records of grain elevator explosions have been documented for over 120 years. However, they have probably occurred from the time that structures for handling large amounts of grain were first developed. Five elevator explosions in the United States in December 1977, resulting in 59 deaths and 48 injuries, raised concern in the Federal Government about how to reduce such disasters. This concern led -- as is often the case in issues of national concern that involve science, economics, and technology -- to calling on the National Academy of Sciences for an objective perspective.
National Academy of Sciences
The Department of Agriculture engaged the National Academy of Sciences (NAS) in 1978 to conduct a symposium on grain elevator explosions. Following this symposium, the Department of Labor's Occupational Safety and Health Administration (OSHA) requested the NAS to form the Panel on Causes and Prevention of Grain Elevator Explosions. Its membership was composed of experts in systems analysis, explosion dynamics, investigations and prevention, instrumentation, grain handling and processing, agricultural insurance practices, employee relations, dust control methods, and aerodynamics.
This Panel's work, completed in 1983, resulted in raising awareness in the grain handling industry of the hazards of grain dust as well as providing specific means of reducing those hazards. Based on that awareness and following extensive debate and Congressional hearings, OSHA issued regulations governing grain elevator operations which have resulted in a dramatic reduction in frequency and severity of elevator explosions during the past decade. The results are graphically shown in Section III of Appendix A, page 214.
Analysis of Previous Elevator Explosions
From 1979 to 1981, the NAS Panel on Causes and Prevention of Grain Elevator Explosions investigated 14 grain elevator explosions in Iowa (1), Kansas (1), Minnesota (4), Missouri (1), Nebraska (4), North Carolina (1), South Dakota (1), and Texas (1). Twelve of the 14 primary explosions were followed by secondary explosions -- which generally caused most of the resulting damage. This on-site analytical work was the first known effort to develop and apply systematic methodology for investigating grain dust explosions.
Prior to this time, most insurance companies and elevator owners only sought to resolve the amount of policy coverage for loss recovery. Though many explosions were spectacular and even killed numerous people, public attention to them was short-lived. By the time causation was determined (if it ever was), it was seldom newsworthy because awareness of the disaster had already passed from public consciousness and concern.
While all 14 elevator explosions were unique in some respects, they had generic commonalties which readily led to universal but practical concepts on their prevention. The results of these investigations were published by the National Academy of Sciences in a series of documents which are listed in the References.
GEEIT (Grain Elevator Explosion Investigation Team)
Following the DeBruce Grain elevator explosion on 8 June 1998, some members of the earlier NAS Panel on Causes and Prevention of Grain Elevator Explosions were contacted independently by various insurance companies and attorneys as well as OSHA to explore whether they might be willing to voluntarily regenerate the Panel to assist in investigating the DeBruce Grain elevator explosion in Wichita to determine causation as well as propose preventive measures. Two original Panel members were now deceased, but the remaining five members agreed to join together under a new title -- Grain Elevator Explosion Investigation Team or GEEIT. Specialists from Wilfred Baker Engineering in San Antonio were enlisted to replace expertise of the two deceased members.
The solicitation by several parties to engage and underwrite GEEIT expertise for the DeBruce Grain explosion presented a dilemma because those parties had differing -- if not conflicting -- interests in GEEIT findings and conclusions. After due consideration, GEEIT decided to accept OSHA sponsorship and provide its expertise to OSHA in the conviction that the broadest and most meaningful contribution to prevention of future explosions would be possible through OSHA's established regulatory framework. Though regulatory bodies like OSHA cannot prevent explosions -- only those parties who control the situation in which explosions occur can prevent them, GEEIT believes that government agencies provide the vital singular role of representing public interest and serving as the public's advocate for safe operation. Further, there was conviction that the traditional OSHA regulatory role could be enhanced if GEEIT provided an educational perspective on the disaster that would support future preventive work by OSHA.
Chapter 2 | Executive Summary of Explosion
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.
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.
Beneath all the 310 silos were four 1,300' tunnels, approximately 7' high and 8' wide -- two under the north array of silos and two beneath the south array. These tunnels in this report are numbered. The tunnels in the south array are #1 and #2, in the north array #3 and #4, with #1 and #3 on the west and #2 and #4 on the east. The conveyor belt numbers coincide with the tunnel numbers. These tunnels contained belts that carried grain discharged from the silos toward the elevator legs in the headhouse. There the discharged grain was elevated and distributed into either a rail car or truck -- or returned to a silo (if the grain had been cleaned, fumigated or aerated).
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
- Outside west tunnel, south array: One fatal
- Outside east side of headhouse: One fatal, one injured
- Inside upper headhouse floors: One fatal, three injured
- Inside south gallery: One injured
- Outside end of south array: Three injured
- Inside west office of headhouse: Two injured
A total of seven men were fatally injured in the explosion. They were employees of either DeBruce Grain or Labor Source Incorporated (LSI).
- Jose Luis Duarte (41 years)
- Howard Goin (65 years)
- Lanny Owen (43 years)
Labor Source Incorporated (LSI):
- Victor Manuel Castaneda (26 years)
- Raymundo Diaz-Vela (23 years)
- Jose Prajedes Ortiz (24 years)
- Noel Najera (25 years)
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.
- Scott Mosteller (37 years)
- David Pickens (21 years)
- Johnny Sutton (46 years)
Labor Source Incorporated (LSI):
- Carlos Amador (35 years)
- Vladimir Martinez Duarte (24 years)
- Miguel Rios (26 years)
- Santiago Sergio Sola (30 years)
- Daryl Williams (45 years)
- Raymond Hamilton (58 years)
Rob Heimerman Trucking:
- Bill Helms (40 years)
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.
- Kelly Burtin
- Brent Hultgreen
- Denise Michelle Tiffany
- Dale Lock
- Steve Stallbaumer
Industrial Maintenance, Incorporated:
- Roger L. Heath
- Tom McHugh
- Rodney L. Schumock
- Eric Mingle
- Bill Dusenbery
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.
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.
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.
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.
Chapter 3 | DeBruce Grain Elevator History
The original grain elevator on the site of the DeBruce Grain elevator which was destroyed on 8 June 1998 was constructed by Chalmers and Borton of Hutchinson, Kansas -- now known as Borton, Incorporated -- for the Garvey Grain Company. This forerunner elevator structure was erected during 1953 and 1954 in a northeast/southwest orientation about 4 miles southwest of Wichita, Kansas.
Upon completion, the elevator complex consisted of a tall, square headhouse centered in-line between two identical arrays of grain silos -- 30' in diameter and 120' high -- arranged three abreast. Maintaining this same symmetry, both ends of the elevator complex were extended in 1955 when an equal number of additional silos were added to each array. The circular silos were tangential in their arrays, forming between them star-shaped spaces, which were also used for grain storage. These spaces were known as interstice silos. The total capacity of the expanded elevator was 20.7 million bushels.
The symmetrical and equal additions, designated as storage units K and L on the Borton engineering drawings, consisted of 33 silos -- eleven rows of three circular silos abreast, with associated interstice spaces. These new silos were numbered as 1000-series silos in the south array and 1100-series silos in the north array. Their addition brought the total number of silos in the complex to 310 -- 246 circular and 164 interstice.
Physical Dimensions and Characteristics
With the completion of the 1955 extensions to the elevator complex, its total length along its longitudinal axis was 2,716 feet. Its major width -- determined by the arrays of three 30'-wide silos abreast -- was about 92 feet. The headhouse stood at the center of the elevator complex, both before and after the extensions.
The tallest and center structure in the elevator complex -- independent from the two silo arrays -- was known as the headhouse. It stood approximately 197 feet above ground level and 216.5 feet above its subterranean basement floor. It was square in cross-section, measuring about 42 feet on a side.
There were entranceways into the headhouse in the basement, at ground level, and from the gallery level. It contained a considerable variety of grain handling and conveying equipment, including four separate elevating legs for lifting grain from the four underground tunnels as well as from truck and rail dumps at ground level as shown in Figure 3-1.
There were two offices in the headhouse. The layout for the scale office, located on the scale floor, is shown in Figure 3-2. The headhouse office was on the work floor at ground level as also shown in the same Figure. Note that the floor plans must be rotated 90 degrees counterclockwise to be consistent with the elevator drawing to the left of the individual elevator floor drawings.
The headhouse floor at the gallery level, sometimes called the bin deck, is where the endless 3,000' grain conveyor belts -- having risen vertically through the work floor (as depicted in Figure 3-2) in the headhouse from the underground tunnels -- turned horizontally and proceeded outward, both north and south, from the headhouse into the galleries as depicted in Figure 3-3. Each of these belts ran through one of the four tunnels under the silos, bringing grain discharged from silos back to the headhouse. Every silo -- whether circular or interstice -- was serviced by one of these looped belts.
There were four vertical bucket elevators, sometimes called "legs", inside the headhouse whose plan-view locations are seen in all three floor plans of Figure 3-2. Each leg consisted of many buckets mounted on an endless belt that (a) scooped grain from a loaded pit, (b) lifted the grain vertically to the top of the elevator, and (c) dumped the grain into weighing and distributing facilities as it turned over and descended with empty buckets to be reloaded. The No. 1 leg had the largest carrying capacity for grain -- 28,000 bushels per hour -- and each of the other three could carry 16,000 bushels per hour. The headhouse contained two scales, as shown in Figure 3-2. Also a belt manlift, which passed vertically through all three floors illustratedin Figure 3-2,was used by workers to gain access to the upper floors in the headhouse and to galleries. A ladder inside the manlift was used by rescue personnel to extricate and lower injured workers from the elevator's scale and machinery floors down to the bin deck level following the explosion.
A floor in the headhouse known as the "bin deck" was at the same 120-foot level as the silo tops. That floor was connected, via two gangways in both directions from the headhouse, to a surface on top of all silos which formed the floor for a gallery (sometimes called "Texas House") with a width of 46 feet and a height of 10 feet. So there was a south gallery and a north gallery running the entire length of the north and south silo arrays. In both galleries, there were two parallel conveyor belts that carried grain outbound from the headhouse where the grain was diverted off the belt with a "tripper" into a selected silo for storage.
There were two sets of parallel tunnels that connected the basement of the headhouse -- one set for the north silo array and one for the south.
These two tunnels -- 7.5' high and 8' wide -- were well below ground underneath both the south and north silo arrays. Within these tunnels were continuous gallery-tunnel belts that transported grain -- being discharged from the silos onto the belts -- toward the headhouse where it was elevated by one of the four legs.
In 1955 when the two new extensions were added to both the north and south ends of the existing elevator, the four tunnels (two underneath each array) were not only extended to the full length of the expanded silo arrays. These two parallel tunnels beneath each silo array were also connected to each other, at the point where the new additions joined the old structure -- between 900 and 1100-series of silos in the north array and between the 800 and 1000-series in the south end. These two connecting tunnels were called crossover tunnels, and they made it possible to work in both tunnels -- without requiring workers to go above ground to re-enter adjoining parallel tunnels only at their ends.
Though these crossover tunnels enabled greater tunnel-to-tunnel access for workers, they contributed to far greater elevator damage during the explosion than had they not been there. It is likely that some of the fatalities resulted primarily because the blast wave from the initial explosion in the east tunnel of the south array not only progressively continued to the headhouse -- as it set increasingly more grain dust into suspension to explode -- but also turned and progressed through the south crossover tunnel into the west tunnel where it was deflected both south and north. Had that avenue not been available, at least one fatally-injured worker who was blown upward over 100' at the entrance to that crossover tunnel probably would not have been injured.
Lean-To and Flat Storage
Garvey Grain added some additional storage capacity in the mid-1950's alongside the east side of the elevator. Although originally intended for storing overflow grain, they have been used for a variety of purposes beside grain storage. Adjoining the silos in the south array and running parallel the full length of that array was a large lean-to structure. It had an underground tunnel -- containing a conveyor belt -- that ran parallel to the main elevator from the south end of the elevator to the truck dump opposite the headhouse. At that point, a connecting tunnel carried grain -- by a crossover tunnel -- into the elevator legs.
Beside the north silo array and also on the east side of the elevator complex, a series of 8 additional, parallel, flat storage units were erected. Similar in function to the lean-to structure, these units were built perpendicular to the elevator complex. Each had its individual tunnel, carrying grain on conveyor belts to the headhouse via a variety of manifolded tunnels. Because both the lean-to structure and the flat storage sheds (which can be seen in Figure 2-1) had not been used for grain storage in recent years, the tunnels underneath them had not been cleaned. Blast waves did enter these tunnels, however, causing substantial damage to their roof structure where energy was vented, but it was not considered consequential in the overall damage assessment.
Continuous Gallery-Tunnel Belts
These 3,000-foot belts as illustrated in Figure 3-3 almost defy imagination. To keep them aligned over such great distances was almost an impossibility. Whatever theoretical economy was gained in initial belt cost had to be forfeited by upkeep expense. Expansion and contraction was accommodated by take-up pulleys. Using both sides of the belt for grain transport meant constant flexing. Most seriously, grain dust constantly accompanied the belts -- both in the galleries and in the tunnels.
Grain Dust Control
The Garvey Grain Company had installed pneumatic dust control systems throughout the elevator complex during the period it owned and operated the elevator. The Mac Pneumatics Company had installed its "laminar flow" system on legs Nos. 3 and 4 and a dust cleaning hopper in the truck dump. In addition to the truck dump, there was also a railcar dump that could unload two hopper cars at time. Within the elevator complex, pneumatic dust collection systems were used in a variety of locations -- along with dust collection filters -- to collect and remove the powdered grain that is inevitably produced by moving grain. DeBruce was reported to have spent about $100,000 to rebuild two of the dust collection systems following purchase of the elevator. Yet, on the day of the explosion, witnesses testified that none of the systems were working -- as all dust collection tanks had completely filled, backing up and plugging those pneumatic systems.
Several workers had died in this elevator throughout its history prior to the 8 June 1998 explosion. For example, during confined space entry work in 1978 and 1983, two workers died. The 1983 death resulted in both an OSHA investigation of the death as well as an inspection of the elevator. This was the last time OSHA had visited this elevator until the explosion. However, the US Department of Agriculture had recently cited DeBruce at least twice for excessive grain dust in the galleries. These violations were not reported to OSHA, and this lack of communication between two Federal agencies created some political furor following the explosion.
There had been several fires in the elevator complex that were extinguished by elevator workers. One fire, about a week before the 8 June 1998 explosion according to worker statements, occurred in the east tunnel of the south array -- near the area where the explosion originated. Minutes of a DeBruce safety meeting held on 29 January 1998 said: "Report a fire, even if the fire has been taken care of. Chances are a hot bearing caused the fire and it needs to be replaced." This acknowledgement about hot bearings is significant on two counts: (a) it would confirm acknowledgement by many workers that there was no preventive maintenance and scheduled lubrication of the conveyor system, and (b) it affirms that DeBruce recognized the linkage between hot bearings and ignition of grain dust.
Such fires were obviously precursors to explosion that only lacked the dispersion of fuel-and-oxidizer within the limits of explosivity that occurred on 8 June 1998.
Chapter 8 | Analysis of Explosion
The series of explosions that devastated the world's largest grain elevator began with a single event -- ignition of grain dust within an enclosed part of that elevator.
The key to preventing another such explosion is to determine the location and enabling mechanism of that critical single event. The massive structural damage and distribution of resulting debris that resulted from the DeBruce elevator could readily hide both of those factors. An overwhelming challenge to "bringing order out of chaos" awaited anyone who searched for them. Yet, on the other hand and based on extensive experience gained in investigating many other grain elevator explosions, GEEIT was confident of determining both the location and enabling mechanism that ignited grain dust.
Two major classes of evidence were available to GEEIT investigators in its search to determine that singular initiating event:
First, elevator wreckage and debris -- together with marks, patterns, residue, and scorching -- provided objective evidence useful in establishing the initial ignition as well as the direction and intensity of ensuing fire and blast wavefronts that were propagated throughout the complex. Second, injuries sustained by both the fatalities and survivors provided insight regarding blast and flame. Third, a massive amount of grain dust was observed throughout the elevator structure.
First, recollection of visual and auditory observations of the explosion by (a) injured survivors, (b) uninjured employees and others on elevator property, and (c) eyewitnesses external to elevator property provided information useful in evaluating physical evidence. Second, those who could recall and describe conditions in the elevator immediately prior to the explosion (e.g., condition of equipment, state of grain moving operations, amount of grain dust available, and elevator personnel assignments) provided additional insight required to analyze physical evidence.
Physical evidence was primary. Witness testimony -- taken in toto -- was acknowledged as secondary, since human sensory perception is recognized as widely variable and cannot be accepted as wholly reliable. However, despite its subjectivity, various types of testimony were very valuable in integrating disparate elements of physical evidence and assisting in resolution of otherwise inexplicable gaps among physical factors.
Process of Analysis
Collection and examination of physical evidence by GEEIT was conducted simultaneously with pursuit of witness testimony. On 22 June 1998, GEEIT on-site interviews began to be conducted with contract maintenance personnel, independent contractor survivors, injured employees, victim families, and eyewitnesses. These extensive interviews were videotaped with permission of each witness.
GEEIT access to the elevator wreckage was limited at this time because grain fires were still being extinguished and search-and-rescue operations for victims were still in progress. However, a series of subsequent GEEIT visits to the elevator resulted in progressively increased access to various portions of the elevator -- particularly the headhouse basement, galleries, and tunnels. In addition, OSHA personnel provided significant assistance to GEEIT in conducting videotaped interviews, investigating and photographing portions of the elevator headhouse prior to its demolition, and undertaking hazardous searches of tunnels to seek -- under the tutelage of GEEIT -- physical evidence of explosion dynamics.
Subsequent in-depth interviews and depositions of key executives, workers, and additional witnesses were conducted. These sessions provided considerable background data and information that supplemented earlier-obtained intelligence.
Because witness testimony was available well ahead of GEEIT access to examining physical evidence, the former influenced the search for the latter. Yet, recognizing the primacy of physical evidence, care was taken to pursue and examine any and all evidence whether or not it agreed with witness testimony.
A combination of deduction -- reasoning about particular findings from general or universal premises -- and induction -- inferring generalized conclusions from particular facts -- was used in the search for ignition. The resulting conclusions are probabilistic (probable but not absolutely certain) rather than determinate (conclusively and irrevocably determined).
Seeking Explosion Initiation
The elevator was destroyed by a series of -- perhaps as many as ten -- explosions . Most witnesses heard but one explosion -- more than likely because individual sounds were either combined into one large report or the sound of the explosion closest to the witness overpowered all others. Since the elevator was over one-half mile in length and both ends of the elevator blew open, it followed that (1) no single explosion could have produced the destruction and (2) a person in close proximity to the elevator would likely only hear the explosion closest to them.
Witnesses at some distance from the elevator were more likely to hear or observe multiple explosions than anyone close to one of them. Two eyewitnesses interviewed at length who were located between 0.2 - 0.5 mile from the elevator confirmed more than one explosion. A third witness, who was in his home 7.5 miles east of the elevator, reported hearing over five distinct explosions in rapid succession. The observations of these three witnesses is summarized as follows:
Witness No. 1
A construction worker, who was familiar with grain elevator explosions from having to rebuild them after previous disasters, was about one-half mile to the west of the elevator facing it while standing on an open industrial structure 40 feet above the ground. He heard a loud explosion which caused him to focus on the elevator. His first sighting was of black smoke emanating horizontally at ground level from the headhouse in both north and south directions between a line of standing rail cars and the base of the elevator. A split second later, the headhouse exploded with a bright orange fireball that blew out horizontally to the west and vertically to twice the height of the headhouse (approximately 500 feet).
Witness No. 2
An office worker in a small building about 1,000 feet east of the elevator had stepped out of a north-facing door in the building onto a porch to check the weather. As his eyes slowly swept about 90o from north to west, he saw a fireball blow out horizontally toward him from near the top of the north array of silos, with fire then rising to the gallery and proceeding north in a series of explosions to the north end of the elevator.
Witness No. 3
A graphic artist employed by a newspaper was in his home which is 7.5 miles due east of the elevator and located on a slight rise which allows direct line of sight to the elevator. He was about to step into the shower when he heard a series of 5 to 7 or more explosions in close order. Due to his Navy experience where he had witnessed a plane crash and then cartwheel with successive explosions in his neighborhood (and since his home is in an airport flight path), he immediately believed that there had been a nearby aircraft crash. Throwing on some clothes, he ran outdoors expecting to find smoke, but it was so overcast, he didn't see any. The series of explosions woke his not easily awakened 18-year old son who asked, "What was that?" They turned on the radio and got the first report of the elevator disaster, whereupon they drove to the site. This witness described the series as consisting of a few blasts followed by 2 or 3 very severe blasts, with the series dying off with smaller explosions. They were not evenly spaced in time, with some coming in rapid succession while others had more separation.
Narrowing the Search
All five components of a grain dust explosion (the Explosion Pentagon discussed in Chapter 7) existed at the DeBruce elevator on 8 June 1998. The fifth and final sequential component -- ignition -- would provide the primary clue as to where the explosion originated. So finding the initial ignition location became the prime focus at the outset of investigation. The ignition of the first explosion was of greatest interest. The testimony of Witness No. 1 was influential in concluding that initial ignition occurred (a) prior to the headhouse exploding, (b) at ground level rather than in a gallery, (c) closer to the south end of the elevator than the north end, and (d) where rubber was a combustion product (to produce black smoke).
Testimony of many additional witnesses provided other clues related to locating initial ignition. A survivor in the south gallery testified that a flame front proceeded from the headhouse south toward him and became extinguished after only a short distance farther down the gallery when it was vented. Another witness reported the ground shaking violently just prior to a fireball erupting vertically from the truck dump on the east side of the elevator.
Combining Physical Evidence with Witness Testimony
GEEIT access to tunnels -- all four of which were filled with spilled grain due to blast wave displacement or destruction of most silo blast gates -- occurred first in the south silo array of the elevator. Considerably more grain had been removed from that array's two tunnels than the two in the north array because searching for and recovery of victims had occurred in them. Because witness testimony definitely favored the south array as most likely site of initial ignition, early south tunnel access proved to be most favorable.
Determining the Initiating LOCATION
The location of the ignition source in the DeBruce elevator east tunnel of the south array (Tunnel No. 2) was determined with considerable assurance by using physical evidence. The surfaces within all the tunnels were heavily coated with adhering grain dust which blackened (from being burned) as flame fronts passed through the tunnel. This black coating contained scars, scratches, scrapings, and other physical signs implanted by various pieces of material and shrapnel propelled in the blast wave. These signs were directional -- they pointed like arrows from where the blast came to where it went. In addition, there was unmistakable evidence provided by silo blast gates and other permanently attached items like light fixtures or conduit which were bent, as shown in Figure 8-1, in the direction that the blast wave had gone.
Determining the origin point for the first blast wave - the initiation of the primary explosion -- was based on these directional signs. It was at that point in the tunnel where the physical signs pointed away in both directions -- from "ground zero." At thatprecise point, there were no directional signs or arrows. In one direction, they pointed away from "ground zero." And in the other direction, they also pointed away. That point was located in Tunnel No. 2 in the south array near Bin 1023.
Locating the Enabling MECHANISM
The second desired objective was to find the enabling mechanism or what ignited the grain dust. At the point of ignition the severity of explosion is obviously minimal. In some cases initiating evidence is destroyed. However, a search of "ground zero" by OSHA personnel proved successful because the badly worn roller -- shown in Figure 8-2 -- which had supported the grain transport belt in Tunnel No. 2 was found. The roller bearings in that roller failed causing the edge of that roller to drop onto the suspension mechanism preventing rotation and fixing the position of the roller. In that position, and because the belt continued to run over it and wear it away (like a razor strop), it had been heated to a sufficiently high temperature that several scenarios could be postulated for igniting grain dust which had collected inside the roller.
At some point in time, smoldering grain dust more than likely was either lifted, dropped or propelled into a cloud of suspended grain dust in the vicinity of the belt which was running at 8+ mph -- providing that fifth component required for grain dust explosion.
The enabling mechanism -- being of sufficient weight to remain near "ground zero" -- was concluded to be a frozen belt roller that was heated by belt friction to ignition temperature.
This roller was sent to metallurgists at OSHA's Salt Lake Technical Center for analysis, along with portions of the conveyor belt from that area, an undamaged comparable idler roller, samples of representative grain dust for that area, and portions of the conveyor support structure. The results of this extensive reflected light microscopy SEM and EDX testing were conclusive that the roller had been heated to about 260 degrees C. The tested grain dust at that temperature appeared the same as the color of the grain dust on the edge of the parabola wear area on the roller. (Photographs and analytical details of these laboratory tests are included and available in appendix A.)
The Ignition Identification Process
The point declared to be "ground zero" was the location for the originating explosion. That explosion was in a plane of symmetry -- force going both ways away from it -- and in concert with all other explosion propagation throughout the elevator complex.
The ignition source -- a failed bearing on a conveyer roller -- which was located at this point was not the only possible source of ignition located in the elevator. However, none of the other candidate sources were located appropriately with respect to the path of explosion propagation. Using aerodynamic theory, the direction of flow of an explosion through a facility can readily be established through observations related to drag forces, pressure forces, and impact damage.
Layered Dust Accumulations
In a grain elevator explosion, the energy which supports it is derived from the combustion with air of grain dust. Hence, this dust must be present at all locations where the explosion propagates. It is absolutely impossible to have a grain dust explosion without the presence of grain dust, whether suspended or layered. It was not difficult to find within the exploded elevator more than adequate quantities of grain dust to fuel an explosion. Copious amounts of dust were accumulated throughout the elevator on various surfaces and even within dust control systems -- most of which were inoperative. Figure 8-3 is only one example of "billowed" dust typical of myriad's of locations throughout the elevator where copious amounts of grain dust remained -- even after the explosion.
Quantities of this dust were sampled at widely divergent locations in order to document that it was indeed finely divided combustible organic material. The amount of dust present in almost all locations clearly exceeded the 1/64" layer needed to explosify an eight-foot ceiling volume. Further, it violated the widely-held rules of thumb concerning seeing one's footprints or the ability to write in it on a wall. Video tapes recorded the presence of unbelievable quantities of grain dust throughout the elevator.
Blast Pathways of Progression
The blast damage at the DeBruce elevator was more severe than any previously observed by GEEIT members in their investigation of 14 grain elevator explosions. Without doubt, this vast damage resulted from (a) ample amounts of available grain dust, (b) large areas of surface roughness, (c) extensive length-to-diameter ratio of confining structure, and (d) absence of venting in all the substantially-constructed tunnels. Figure 8-4 summarizes the following discourse on the sequence and direction of blast waves through the elevator.
South Silo Array
The south silo array, in which the explosion originated, suffered the least damage. However, it was severely damaged as the explosion vented out the south end tunnels, the crossover tunnel between the 800 and 1000 series of silos, and at the headhouse. The south gallery vented at the bridges between the complexes, the windows, and the south end. Workers near the venting of high pressure gases or those engulfed by the explosion in the south array were fatally injured by a combination of overpressure, thermal exposure, impact, and shrapnel.
The northward traveling explosions in both the south tunnels entered the headhouse -- but not necessarily at the same instant. As they arrived, explosion propagated upward in the headhouse as shown in Figure 8-4 and was vented effectively from the basement, through the truck and rail dumps, and the work floor. It then continued venting at the bin deck (at the gallery level), distributor, garner, and scale floor levels -- effectively enough that the headhouse roof was preserved. Additionally, the blast traveled eastward into the truck dump where it vented upward around the truck that was unloading in the dump closest to the headhouse. In the outer truck dump, it vented into a north-south tunnel under the flat storage lean-to located along the east wall of the south array where it vented upward through the floor. This collective venting produced substantial blast and fragmentation damage in the immediate vicinity of the headhouse.
At the gallery level in the headhouse, explosion vented into both north and south galleries. In the south gallery, sufficient venting was available around the 400-silo series to decouple the pressure front and the combustion process, thus allowing the explosion to attenuate. A modest overpressure did, however, continue traveling to the south end of the south gallery.
More severe venting occurred in the east and west sides of the headhouse than north and south. Note in Figure 8-5 the west or rail side of the headhouse where the rail shed is destroyed. It was there that a railcar was derailed sideways (to the west) by a blast wave emerging from the headhouse.
North Silo Array
The worst structural explosion damage in the elevator occurred in the north silo array due to near-simultaneous explosions in the tunnels, gallery, and individual silos. As the explosion left the headhouse, it traveled north in the north gallery for its complete length. But also from the north gallery, a blast wave traveled down to the west tunnel (Tunnel No. 3) via an interstice space located in either the high-100 or low-300 silos series. In Tunnel No. 3, the blast was diverted both south toward the headhouse and outward toward the end of the north array. At the south end of Tunnel No. 3, the explosion entered the headhouse basement and then vented to exhaustion.
At the crossover tunnel between 900- and 1100-series of silos which connected Tunnels No. 3 and No. 4, the explosion from Tunnel No. 3 crossed over to Tunnel No. 4 where it bifurcated -- traveling south toward the headhouse, straight ahead into a tunnel connected to Number 4 flat storage building, and north toward the end of the north array. By the time the wave exited Tunnel No. 4, there were no more explosions within the elevator complex, as all possible locations had been traversed.
Limited venting provided by north gallery windows and bridges did not attenuate the blast wave. It descended downward into the north west tunnel. Observable structural damage within those tunnels was quite high at some locations -- particularly at the north end of the array. As blast waves exited at that end, the resulting disintegration produced an extensive debris field of small fragments which were widely distributed. Based on conclusions drawn from an explosion of a Pillsbury elevator in St. Joseph, Missouri which was investigated by GEEIT members, there may have been a transition from deflagration (subsonic burning) to detonation (supersonic burning) in the combustion process.
While the concrete structures and metal contents exhibited pressure-resultant damage, the accompanying flame front burned humans and caused the ignition of smoldering grain fires that burned for weeks after the disaster.
Quantitative Analysis of Damage
Numerical estimates of the magnitude of structural damage as well as blast forces were calculated based on physical measurements obtained at various points in the elevator complex. The details of this analysis is contained in Appendix A.
Evidentiary Foundation of Analysis
It should be noted that the pathways of explosion are supported by physical evidence. Several hundred photographs and dozens of video tapes were made in support of the investigation. From these, a separate compendium of 130 photographs -- with accompanying written rationale and descriptive video summary -- was prepared entitled "Blast Investigation Group Report." This report is contained in its entirety in Appendix A.
GEEIT did not arrive on the scene of the explosion until 22 June 1998 -- two weeks after it had occurred. Therefore, it was not possible to evaluate that phase of the explosion.
However, since rescue does involve factors that may provide clues and enhance the investigative process, extensive interviews with fire and rescue personnel were conducted by GEEIT. A personal account of rescue often provides the best insight on this important facet of the explosion. The following narrative was written within hours after the incident by Wichita Fire Department Captain Billy Jack Wenzel as a personal journal. He has given permission for its inclusion in this report.
"On June 8th 1998 at 0918, a grain dust explosion caused extensive damage to one of the largest grain elevators in the world. By 0945, a request for all on-duty Rescue Team members was sent out. I arrived at the scene at 1010."
"We first responded to the south end of the elevator. We were taken to the place where workers were last known to have been located. We walked past dump trucks and skip loaders that had been in operation when the blast had occurred. All had an extreme amount of damage. The fiberglass of the dump trucks was shredded, all windows were broken out, and pieces of concrete the size of desks were laying on the equipment. I knew that the operators must have run for their lives because the equipment was still running."
"Upon reaching the area of the known workers, I found my first victim (Jose Prajedes Ortiz). He had been blown clear of the structure -- not a stitch of clothes remained on him. I got a tarp and covered him. We were informed that the other workers had been in the tunnels under the elevator. Most of the tunnels were now filled with rubble, and from what we could see, the grain in the bins had been dumped into the tunnels."
"The access area to the tunnels originally had grates covering the access. I knew this because one of the grates was now wrapped around a beam 120 feet above me on the bottom of the catwalk at the top of the elevator. The explosion was massive! We called several times into the tunnels. There was no response."
"We were then informed that a live victim had been seen near the central headhouse on top of the structure. A crane was being brought in to lift rescuers to the top. Our Rescue Team members were divided into four-person teams. I was assigned with Captain Slaughter, Lieutenant Ast, and Firefighter Dowty. Our group was assigned reconnaissance duty."
"We were the first Team to the top of the structure. The crane was positioned on the west side, just north of the central headhouse. We were set down on one of the few north array silos that were still intact. As soon as we unloaded onto the roof, we tied into each other with ropes and harnesses. We positioned one rescuer at the end, another ten feet back, and the other two some forty feet back. The first two would advance, the other two would meet them."
"Moving this way, we found our first live victim (Scott Mosteller). He was on the roof of the north silos on the east side. When he saw us, he started to come to us. We had to caution him to stay put. When we arrived at his location, it was obvious that his injuries were serious. His hands and face were burned badly. We had to assist him back to the crane basket and into it. He was totally unable to use his hands. I later found out that this victim had been using his cell phone to talk to his family before we found him. (See Figures 8-6 for Scott Mosteller and Figure 8-7 for rescue crane)"
"With that victim removed, we returned to reconnaissance. Although there was a lot of smoke, most of the fires seemed to be small spot grain fires and not of major concern. We could not proceed north because the tops of the silos had been blown off, and there was no way to pass over the open silos. (See Figure 8-8 for destroyed silos) We started our reconnaissance south toward the headhouse."
"We eased through the rubble to the west catwalk. Lieutenant Ast crossed the catwalk and peered into the open doorway. The floor was gone. It lay in a pile of rubble several feet below. He called out several times with no response. We backed out. We then moved to the east catwalk. Lieutenant Ast again made his way across the walkway to the door. I again followed, staying a few feet behind. The floor again was gone. We called, 'Is anyone here?' There was no response from the rubble below. Again we backed out. Even though the floor was gone on this level, I noticed that the ceiling was intact. I knew we had to get above."
"We moved outside to the top of the intact silos where we had removed the earlier victim. From there, we found a ladder leading from the silos to the roof of the headhouse. Lieutenant Ast, Firefighter Dowty and I made our way to the roof. It was at this time that the helicopter from Fort Riley arrived and was being used for aerial reconnaissance. The vibration from this helicopter made the entire structure shake. I asked Captain Slaughter, who was in radio contact with command, to have the helicopter grounded while we were on the structure. He had to move inside to escape the loud noise."
"Firefighter Dowty and I again tied ourselves off. From the roof, we moved down a ladder to the roof of the catwalk. Lieutenant Ast tied off our rope to the ladder, as Firefighter Dowty and I slowly crossed the catwalk roof. The only entrance to this level was a window. It was about six feet above the catwalk roof. Firefighter Dowty pulled himself up and called out."
"'We are in here,' was the reply. Dowty turned to me and said, 'I have voice contact with a victim.' I relayed this information to Lieutenant Ast, and he in turn to Captain Slaughter. We spent the next few minutes getting information from the victims (Johnny Sutton and Lanny Owens). They were not in the room with the window. They were one level up. There were two of them. Both were breathing, but only one was talking. We told them to stay where they were, that we were on our way."
"I gave Firefighter Dowty a leg up, and he entered the room. I asked Lieutenant Ast to come to my location and give me a leg up. While waiting for Ast to make it to my location, I took a close look at the tower I was getting ready to enter. Large holes were blown out of the east and west walls. The north wall -- the one with the window I was getting ready to crawl through -- was bulging. Cracks spidered through the entire exterior. Two huge chunks of concrete -- held merely by rebar -- moved in the wind. I remember thinking that if it broke loose, it would wipe out the catwalk, catwalk roof, and me."
"Lieutenant Ast gave me a leg up, and into the room I entered. As I came through the window, Firefighter Dowty moved to the ladder located in the center of this level. I instructed Lieutenant Ast to stay at the window and relay information. I moved to the ladder and followed Firefighter Dowty up. It was a tight squeeze through the floor opening to the next level. The explosion had the floors and walls tweaked. Once on this level, we found the victims. (See Figure 8-9 for Fire Rescue team inside the headhouse)"
"The victims were in a small control room. The west wall of the room was completely gone. The roof had collapsed in a V pattern. Both men were close to the east wall -- one sitting, one lying. The door to the room was on the east wall. The victims told us that the steel door was supposed to open outward. Over half of the door was pushed inward past the steel jamb. I told Lieutenant Ast to ask for a pry bar and a K-12 saw. Meanwhile, Firefighter Dowty used a hammer and screwdriver provided by the victims to remove the door pins, hoping to take the door out of the bind. No luck. The door had two Plexiglas panels in it about 3 feet off the floor. The top one had been blown out. Firefighter Dowty removed the lower one and the metal brace between them. This made a large enough opening to get through."
"I told Firefighter Dowty to enter the room. Both victims were in very serious condition. Both had skin hanging from their burned hands, and their faces were black with burns and smoke. I asked if there had been several explosions. One of them replied he only heard one, and that was all he needed."
"Both victims were eager to leave the room and thought if we helped, they could make it through the window. The victims were unable to use their hands. We placed a chair both inside and outside the window. Carefully, we assisted the first victim onto the chair. With our help, he placed his foot through the window and onto the other chair. Using this procedure, both victims were removed from the room and standing with us on the upper landing. Neither victim could climb down a ladder, not without hands."
"Several Rescue Team members had assembled on the lower floor. I asked for a 30-foot piece of rope. I also instructed those members below to be limited to a bare minimum. As unstable as the structure looked, I didn't think it could handle the extra weight. I knew we were really hanging our asses out. The structure looked as if it could go down any minute. Firefighter Dowty asked us all to say a small prayer that we would all make it out safely. I am not a religious zealot, but I found myself saying a few words."
"Lieutenant Cordts, also a Rescue Team member, climbed the ladder with the rope. I tied a loop, using a figure eight knot and safety. We took the loop and had the first victim step through it. The loop was brought up under the arm pits with the knot at the back of the head. We made two wraps around the rung of the ladder above the victim's head. We held tension as the victim stepped onto the ladder. As he stepped down, we would lower him. I asked the second victim if he knew of anyone else in the area. He said he thought he heard someone on the next level up. We lowered the second victim the same way we lowered the first."
"I then noticed a Battalion Chief on the lower level. I asked the Battalion Chief to keep unneeded people out of the structure. He told me, 'I was the last one in, and if anyone was going to leave, it was going to be me, not him!' I apologized. Firefighter Dowty, Lieutenant Cordts, and I free climbed to the next level -- about 50 feet. As we looked around, Lieutenant Cordts stated that he felt as if we were in Hell."
"As soon as Firefighter Dowty reached the floor, he stated that he had another victim (Darryl Williams). This patient had similar injuries -- burns to his hands and face. His LOC (level of consciousness) seemed to be somewhat diminished, and his hands were really swollen and dripping profusely. We determined that this patient could not be removed as the others had been, with a loop. We placed him in a half harness. It was soon obvious that this would not work because the victim was tipping. He needed a full body harness. Lieutenant Cordts removed his and placed it on the victim. Using a carabiner, we hooked to a D-ring behind the victim's head."
"By this time, Battalion Chief McClure had free climbed to our level. He stayed below the victim and assisted his feet as we lowered him from above. With the victim down, Firefighter Dowty took a quick look on the roof. Then we headed down the ladder. I was last, and I made a quick check of each room on the way out. As I crawled out the window that we had made entry through some time ago, I pulled out a step ladder -- knowing no one should be placed into this dangerous area again. We made our way off the catwalk roof onto the silo roof. We took our gloves off, shook hands, gave each other hugs and high five's."
"Once on the ground, I informed the area commander, Captain Wolfe, that the area was all clear and no other person should be placed in that area. The four victims were lifewatched to area hospitals -- three in critical and one in serious condition. I was on this incident scene for 18 hours. Later I assisted in searching tunnels and moving debris."
Figure 8-10 shows the US Army helicopter rescue of David Pickens from the south end of the south silo array.
Compromise Between Rescue and Destroying Evidence
In every catastrophe involving human beings, there is an inevitable tension that is immediately set into place between (a) the immediacy of rescuing survivors and recovering bodies of fatalities, and (b) the critical need to recover as much undisturbed physical evidence as possible so that causation can be determined. This is true in aircraft crashes, industrial accidents, and terroristic attacks.
Because GEEIT did not arrive on the scene of the DeBruce elevator explosion until two weeks had passed, there was no likelihood that the location and distribution of debris would be exactly as it was the moment that the last explosion stopped. Frantic searching for several victims started within minutes and continued for weeks, until the body of the final fatality had been recovered from Tunnel No. 1 in the south silo array. Admirable efforts were expended by many organizations -- including the Nebraska Urban Search & Rescue Task Force sent by the Federal Emergency Management Agency (FEMA) -- looking in both the headhouse ruins and tunnels in the south silo array for all unaccounted workers. Of course, during this time, there was neither awareness of nor concern for the importance of not disturbing or even destroying key elements of physical evidence in the process of locating and recovering all victims.
Loss of Evidence
Given the inevitability of priority favoring rescue over collecting physical evidence, it was indeed amazing that the activities executed by FEMA had no adverse impact on the investigation conducted by GEEIT to determine the sequence of events leading up to the explosion. Their rescue activities ultimately proved to be in vain, as the conditions produced in a layered grain dust explosion in a confined space -- such as the tunnels, are basically unsurvivable. The human body cannot withstand the damage produced by the high winds, high pressures, and high temperatures created by the combustion process. The body fragments which were recovered from the tunnels verify this analysis. It turned out to be irrelevant as to whether or not there were air spaces between the grain piles in the tunnels. The workers had died in the first fractions of a second after the blast occurred.
The failure of all the dust control systems to operate properly contributed to the layering of significant amounts of grain dust throughout the facility. In the north silo array -- between the 500 and 700 series of silos -- part of a dust collection system was located. During the explosion, this equipment was displaced to the ground level in a drive-through area. As part of the grain salvage operation, this equipment was further moved and damaged, making it difficult to assess its condition at the time of the explosion. It appeared, however, to be clogged with grain dust.
At the time GEEIT arrived on scene, the north truck receiving leg on the east side of the north silo array at the 300 series silos was still mostly intact. However, all of this material was removed before it was possible to conduct any inspection of the modestly damaged components.
At the north end of the north silo array, an extensive debris field of fragmented concrete and damaged equipment was created as the result of the extremely intense final explosions vented from the ends of Tunnels 3 and 4. In the annals of contemporary explosion investigation, this field presented a unique opportunity to collect singular scientific data concerning fragmentation. However, without consultation with GEEIT, this area was scraped clear of this very valuable evidence in order to make it available for grain salvage operations.
The rail dump on the west side of the headhouse suffered the usual venting damage while the covering shed suffered some impact damage during the explosion. GEEIT found it to be of great interest to enter the lower levels of the rail dump in order to attempt to collect ambient levels of layered grain dust -- thereby being able to assess the quality of housekeeping maintained at the DeBruce elevator. Entry into the truck dump on the opposite side of the headhouse had proved to be quite valuable, as excessive amounts of grain dust were found there.
It was GEEIT's understanding -- following a meeting involving all concerned parties -- that during the demolition of the headhouse and the peripheral facilities, the first effort would be directed at the removal of the rail shed. Further, subsequent entry was to be allowed for GEEIT to get into the bottom of the rail dump. This pause did not occur. Shortly thereafter, a substantial part of the top of the headhouse collapsed into the rail dump -- negating the collection of any relevant evidence.
As a result of the explosion, all access to the upper levels of the elevator were removed. Hence it was necessary to be lifted in a bucket suspended on a crane. Accessing different areas required moving the crane. Wind velocity was also a factor with the crane.
In the north silo array where the explosions went the entire length of the gallery, tunnel explosions seemed especially strong. There were also numerous silo explosions. Smoldering fires began in many silos and in the grain which had spilled into the tunnels when the blast gates had been sheared off. These fires are most effectively extinguished by removing burning grain from the elevator onto the outside ground. However, whenever it was possible at ground level, excavations were made into the tunnels and large quantities of sand were poured in to block the supply of air to the fires. This sand also blocked tunnel access for GEEIT. Additionally, large amounts of water were also poured into tunnels to attempt to extinguish fires -- resulting in several feet of water that also prevented GEEIT access.
The electrical vault in any grain elevator is a very important location to investigate following an explosion. It allows verification of equipment operation as well as determination of tripped circuit breakers or blown fuses. In the DeBruce elevator, the electrical vault was located in the northeast corner of the headhouse work floor. During demolition of the headhouse, significant damage was done to the electrical equipment contained in that room, and only an unsatisfactory examination could be conducted.
Almost immediately after the recovery of all but one victim's body, a DeBruce renovation effort was initiated in the south silo array to construct a working grain elevator in time for the September 1998 milo harvest. This meant that spilled grain and damaged equipment was being rapidly removed from its post-explosion setting. Hence GEEIT, in a substantial number of situations, found it necessary to rely upon its initial observations and documentation for evidence pertaining to the explosion. This unusual rebuilding did not occur during the other 14 grain elevator explosions that GEEIT had investigated. These latter cases had allowed revisiting elevators to review and verify data which had been collected. While the DeBruce situation did not detract from the accuracy of the final conclusions, it required that an extensive amount of documentation be collected and reviewed.
The scene of a disaster like the DeBruce elevator explosion is initially chaotic. No one is in charge of anything. Almost immediately however -- particularly if there are people missing or unaccounted for, emergency response by police and firefighters places them in a position of authority. Boundaries are established, and the simply curious are kept at a distance.
For the first three weeks following the DeBruce explosion, Sedgwick County authorities -- both Fire Department and Sheriff -- as well as the DeBruce Grain Company shared access control to the elevator. This created unusual restrictions for GEEIT in its investigative efforts. And it had never been encountered in any of the previous 14 grain elevator explosions in which GEEIT had been involved.
When GEEIT members arrived on-scene and identified themselves as associated with OSHA, entry to the property was initially denied for lack of OSHA photo identification. During the next 3 days, GEEIT access to the elevator was restricted to no closer than 100 feet, presumably because structural collapse was feared -- coupled with uninterrupted search efforts for the final victim. While some information could be obtained from that distance, meaningful data could only be gained by unfettered access.
During 23-29 June, there were a number of unfortunate and unnecessary jurisdictional encounters experienced by GEEIT which ultimately had to be resolved by invoking Federal authority to overrule Sedgwick County authorities to grant GEEIT legitimate access to carry out its mandate. This was a new and unpleasant experience for the GEEIT members involved, and it complicated the investigation as well as increased GEEIT travel costs.
Consideration should be given to the role of expert investigators in any future grain elevator explosions. The National Transportation Safety Board has a similar role in transportation accidents, and their authority to full jurisdictional control of an accident scene -- and all its attendant functions including site security -- is unambiguous. Perhaps the Federal government should extend that mantle of investigatory control to those investigating elevator disasters as well.
Chapter 14 | Prevention of Future Elevator Explosions
Grain elevator explosions are avoidable. There is no mystery about how to prevent them. Yet there is need, from time to time, to remind the entire grain industry about the fundamentals of why elevators explode.
Systematic Management of All Facets
Managing a grain elevator is just like managing any other business enterprise in today's complex world. It must be done with an all-encompassing, systematic perspective. Like a symphony orchestra, all the facets of the business (instruments) matter. They must blend. They must be synchronized. One cannot be emphasized over another.
In 1983, the National Academy of Sciences published the results of its Panel on Causes and Prevention of Grain Elevator Explosions. Central to those findings was the message that only the systems approach would bring grain dust explosions under control. Figure 14-1 was the management keystone in their report.
It is time to reinforce that message. The DeBruce Grain company obviously elected to ignore many of the sectors in Figure 14-1. Once more, it appears that a crisis in the grain handling business exists -- unless DeBruce is an odd exception.
The systems approach begins by recognizing that catastrophic losses, like the 8 June 1998 disaster, occur only after being "set up" by a series of management decisions. Therefore, "let's start at the very beginning, a very good place to start" -- with preexisting conditions.
Grain elevator explosions are caused. They do not happen capriciously or randomly. Therefore, they can be foreseen, predicted, and avoided.
Given widely-held but erroneous folklore about what causes grain elevators to explode, it is incumbent on executives who own and operate elevators to (a) understand and acknowledge the likelihood of explosion, (b) educate and warn their workforce of the five components of explosion, and (c) -- most importantly -- prevent explosions by continually removing the fuel (powdered grain) from all locations in the elevator while simultaneously controlling as many of the wide range of ignition sources as possible.
There is no question but that grain dust is the central issue in all elevator explosions. Its inevitable generation; its high-explosive nature (six times as explosive as black powder); its continued re-introduction -- once collected -- back into stored grain; its adhesion to elevator walls, ceilings, floors, structural components and equipment; and its mandatory imperative of constant removal through diligent cleaning processes all point to the criticality of its ongoing cleansing and purging from all elevator surfaces.
Contrary to the popular conception among grain elevator operators that "grain dust will always be present, so the only way to avoid explosions is to concentrate on eliminating ignition sources," the DeBruce elevator exploded primarily because it was loaded with grain dust. Grain dust collection systems were inoperative -- some having been out of service for over a year. Further, there was no disciplined DeBruce program of manual cleaning to compensate for this lack of functioning dust collection equipment.
So the stage was ideally set for a massive explosion on 8 June 1998.
Just as in many aspects of human life, there are some important principles that govern success in grain elevator management. Some of those principles are worthy of reiteration -- particularly following such an inexcusable catastrophe as the DeBruce Grain elevator explosion. Details of what was found upon in-depth investigation by GEEIT after the disaster allow insight on how to prevent future explosions.
Allowable Grain Powder
In grain industry parlance, the term "housekeeping" connotes a particular operational discipline associated with powdered grain. However, such a catch-all, mundane title may have contributed to its obvious disrespect by DeBruce Grain Company.
Most certainly, the perhaps misleading title (housekeeping) belies the true importance of the need to keep the inside of the grain elevator cleansed from explosive accumulations of grain dust. This is especially true for the small particle sizes that are sometimes referred to as "float dust". Management must instill in their workforce the need to keep to a disciplined routine that maintains the cleanliness of the overall facility. A clean and orderly facility has a positive influence on workers and customers alike -- as well as satisfying regulatory officials, insurance inspectors, and other visitors who may enter the grain elevator structure.
It has long been known that the fuel which powers these severe explosion disasters in the grain handling industry is the organic grain dust. It is made up of small broken grain particles and minute grain particles that result from the abrasion of kernels rubbing against each other and impacting surfaces as they move through the grain handling system from the farm into the commercial grain trade to the final grain processor.
Grain Dust Generation
There are many factors that influence the generation of grain dust. Among the more important ones are:
(1) How the grain is dried. If grain experiences excessive drying in grain dryers -- which may even occur on the farm, this will tend to make the grain more brittle and may cause cracks or fissures in the grains themselves.
(2) How the grains are handled in the stock handling system. Starting at a farm storage facility where grain streams are subjected to free falls from one level to another, the rougher the grains are handled the more breakage can be expected -- beyond the normal abrasion that occurs from movement of grain.
(3) How the grain kernels are coated. Some grains have a natural oily or wax-like coating, which tends to allow less abrasion during grain movement while grains that do not have such coatings are abraded to a greater degree as they are moved, producing more dust. Grain handled gently -- laying them down on a conveyor instead of dropping them in a free fall onto a conveyor -- produce less dust. Mineral oil is occasionally added to the incoming grain stream, and when it is, abrasion between grains is reduced. When pneumatic dust control systems pull off the dust just as it is released from the grain stream at transfer points, less dust is distributed throughout the grain elevator that will have to later be cleaned up.
Re-Distributed, Not Collected
GEEIT interviews with workers revealed that grain dust at the DeBruce elevator was swept using brooms, while air lances were used to "blow down" the dust from overhead and other elevated surfaces onto the floor from where it could then be swept up. However, they said that this dust was put right back into the grain handling system. The dust was thus dumped into silos, placed back on running belts, or pushed into various openings in the grain handling system that were close to floor level. Sometimes dust was even swept down the belt manlift as a means of getting rid of it.
This practice of placing the dust right back into the grain handling system has long been known in the grain industry as a very hazardous cleaning practice. It means the dust that has been removed will be released many more times into other parts of the grain elevator facility only to be cleaned up again and again by workers until either it is shipped out with the grain or serves as the fuel for a disastrous explosion.
Historic But Abandoned Dust Control
In the DeBruce Grain elevator, there had been a number of pneumatic dust control systems installed by Garvey Grain over the years before DeBruce purchased it. Figure 4-1 shows their location. There was one on the truck dump as well as additional pneumatic dust control systems inside the headhouse and other points in the elevator complex. A number of cyclones and dust filter collectors had obviously been in use also in previous years. At the time of the disastrous explosion, none of these pneumatic dust control systems were working effectively as designed -- if they were working at all. This meant that the only DeBruce grain dust control effort was use of occasional manual cleaning.
Lack of Equipment Maintenance
Workers interviewed by GEEIT also revealed that there were many operating problems with the pneumatic dust control systems such that, most of the time, these systems were not operating. This is not surprising after looking -- following the explosion -- at the "filter socks" in several of the filter collectors that were removed from the elevator debris. These "socks" were thoroughly coated with thick dust accumulations that proved that the self-cleaning cycle of these filter collectors had not been working properly. Therefore, air flow through these dust filter collectors was greatly reduced below their designed air flow -- even choked to zero, causing these systems to shut down. Note in Figure 6-4 the spilled contents of one grain dust collector that toppled during the explosion.
Dust cyclones associated with the headhouse also had excessive buildup of grain dust and other foreign matter within them. One was almost completely full, which would indicate that the rotary valves were not functioning properly to keep these cyclones operating the way they were designed to work. This would also cause the cyclone systems to fail to capture the dust emissions at the points they were expected to control.
Grain Transfer Entries
GEEIT investigation of the pneumatic dust control pickup on the drag conveyor from the truck dump to the headhouse revealed that it was also fully plugged or closed. This means the transfer duct was not capable of moving any air through it, nor was it able to capture any more dust emissions from this location. Observations made in this area showed excessive dust accumulations much greater than the maximum allowable 1/8-inch and, in some places, it was several inches deep on the floor. Some nearby surfaces -- even after the explosion blastwave and flame front had passed through on its way to the truck dump from the headhouse -- were covered with deep dust. Had there been any priority to DeBruce housecleaning, most of this area would have been classified as critical.
Further on into the headhouse basement area adjacent to the truck dump drag conveyor, the dust pickup on the underside of the No. 2 looped endless belt conveyor was inspected by GEEIT. The inspection cap was removed from the pneumatic dust control pickup duct at this location. It also showed that this dust pickup point was fully plugged such that the designed air flow was not able to pass through the duct. The dust accumulations in this area of the headhouse on the ductwork, floors and other surfaces were just as great as previously found -- far deeper than 1/8-inch and, in some of these locations, again several inches deep. This location in the headhouse basement likewise should have been a high priority housekeeping area.
On the bin deck or gallery floor level in the headhouse, the pneumatic dust control pickup installed over the top of the No. 1 looped endless belt conveyor -- just at the point where it is loaded with grain -- was inspected by GEEIT. The top of this dust collector hood had several inches of grain dust accumulation where the duct enters the hood. This indicated that the air flow within this pneumatic dust control system for this part of the elevator complex was not working to its designed rate of air flow either. Once more, this area showed excessive dust accumulations well beyond 1/8-inch maximum even on the walls! This was also true forthe dust collection equipment surfaces and the floors into the south gallery adjacent to the headhouse. In any elevator, these areas are always priority housekeeping areas.
The charred dust that still remained on the walls of the headhouse at the bin deck or gallery floor level accessible from both crosswalks from the south gallery side was also inspected. The few wall areas that had been swept were quite noticeable. They appeared to be almost the color of dried concrete or cement -- compared to the deeply charred, blackened grain dust that had adhered to the vertical surfaces everywhere else.
This charred dust, which had originally been "float dust" that had adhered to the concrete wall surfaces, on some wall surfaces looked almost to be 1/4-inch thick in the areas around bucket elevator legs No.1 and No. 2. This pervasive grain dust accumulation on all these vertical surfaces contributed to the intensity of the fireball and its duration in this area of the headhouse.
To overcome or at least minimize grain dust adhesion to vertical surfaces such as occurred throughout this elevator, the grain industry has long advocated painting those surfaces to make them more smooth and thereby reduce the potential for such accumulations. This practice also enhances the ability of workers to clean them more easily due to the smoother surface.
Explosive Fuel in Galleries
According to workers who were interviewed by GEEIT, grain dust accumulations in the galleries were primarily controlled using air lances to blow down grain dust from overhead roof trusses and other surfaces so that it could be swept into the nearest silo hatch that was available. In the south gallery, GEEIT observed that air hoses and air lances were still hooked into the elevator's compressed air piping system after the explosion. Workers stated that there had been a problem with the air compressor the morning that the explosion occurred, so some cleaning efforts were hindered by this equipment problem.
Impact of Cleaning in South Gallery
In the south gallery, some areas just south of where the fireball became disassociated from the blastwave and thereby was extinguished, the overhead surfaces were reasonably clean of excessive dust accumulations. However, going on further south toward the end of the south gallery, the thick grain dust on the floor -- shown in Figure 8-3 -- looked very much like billowed sand looks when it is windblown on the desert or the beach. The tripper in the south gallery was heavily laden with grain dust on many of its horizontal surfaces -- with some surfaces deeply loaded again with well above one inch or more of grain dust.
In all four tunnels, there was so much blastwave damage and grain spilled into them from the silos above them that GEEIT investigation could not determine the exact levels of grain dust accumulations from direct observation. However, interviewed workers stated that in all tunnels both grain spills and grain dust accumulations had occurred -- without being removed for long periods of time. At various points in each tunnel, this conglomerate had formed with ground water a sour chemical composite of sufficient constituency that it could be walked on. Further, it was so heavily deposited alongside the looped endless conveyor belt in each tunnel that the height of the sludge was well above that of the belt as it ran through the tunnel. In fact, workers occasionally had to crawl on their hands and knees on top of this mess to progress through the tunnel.
On 8 June 1998, four of the fatally-injured workers were cleaning up this ugly scene -- at the time of the explosion -- in the west tunnel of the south silo array by shoveling the sour mixture into individual buckets which were then carried to a location where each bucket could be pulled by rope to the surface and emptied into a vehicle that would carry it away to a dump. The No. 1 looped endless belt conveyor in that tunnel happened to be out of service for repairs at the time the elevator exploded, so it was not running through this muck at that time. However, workers testified that it was not unusual for the belt to be operating while this shoveling activity occurred.
Tunnel Impact on Explosion Initiation
Tunnel filth played a major role in enabling the explosion to start at silo 1023 on 8 June 1998. The No. 2 looped endless belt conveyor in the tunnel was running at the time of the explosion. One truck had already been unloaded that morning using this belt. A second truck had pulled in the truck dump and begun discharging its grain into the elevator truck dump. So there was suspended grain dust in the tunnel with absolutely no mechanical collection of it.
As described earlier, the belt conveyor system consisted of multiple rollers to form and support the belt as it ran through the galleries and tunnels. Most of these rollers observed in the galleries and tunnels were cast, normally hollow and rough inside, and open at each end which lent them to accumulating grain dust on their inside surfaces. Of the concentrator rollers observed, few had sealed ends with no openings.
In the south gallery, as an example, excessive dust accumulations had occurred inside of almost all of the inclined concentrator rollers -- even on those where the belt had been running before the explosion. This conveyor roller assembly required special effort to clean and remove accumulated dust -- especially from the inside of concentrator rollers. It is almost certain that such cleaning had not been accomplished on roller assemblies in the tunnels since some coated concentrator rollers were found partially or fully buried in grain and grain dust.
In summary, prevention of future grain elevator explosions is attainable -- but only if these listed, discussed, and confirmed shortcomings by DeBruce Grain Company are accepted vicariously as both meritorious and applicable by all other elevator executives. Should that acceptance fail to be granted by grain elevator operators, the grain industry appears destined to continue destroying property and personnel needlessly.
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