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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.
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
Facets of the Systems Approach to Grain Elevator Explosions
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.
Headhouse Pollution -- 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.
Tunnel Filthiness -- 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.
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.
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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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