Grain Elevator Explosions and Fires
Are America’s 8000 grain elevators just so many time bombs ticking toward eventual destruction by blast and fire? After a century of experience, why are fatal elevator explosions still making headlines? What are the prospects for design changes or protective systems to cut these losses? How can the fire service evaluate elevator hazards?
Before offering any answers, let’s put the problem into historical perspective. The first grain dust explosion reported in this country occurred in 1864. A century ago last May 2, nationwide concern was felt over the catastrophic loss of three Minneapolis flour mills, costing the lives of 18 workers plus over $800,000 damage. In Buffalo 35 years later, 33 persons died in a similar incident.
Extensive research then produced changes in design and operation which have greatly improved the safety record of flour mills. This is not so with grain elevators.
Says an Iowa State University researcher, “In all the recorded history of industrial dust explosions in the United States, grain elevators rank first in number of occurrences, people injured, and amount of property damage. From 1864 to 1956, nearly twice as many dust explosions occurred in grain elevators as in flour mills…”
Elevators are the number one explosion killer. From 1925 to 1956, blasts (and injuries) were five times as frequent in elevators as in other starchprocessing facilities, with deaths and losses nearly 10 times as great.
More recently (1964-1973) the United States experienced 3000 elevator fires each year, with an average annual loss topping $33 million. Explosions average eight per year.
Series of explosions
At home, however, what set off a flurry of activity by government agencies and the grain industry was the series of 43 explosions commencing in 1976, including:
- January 22, 1976, Zilwaukee, Mich.—5 killed, 14 injured.
- February 22, 1976, Galena Park, Texas—9 killed, 6 hurt; damage $42 million.
- May 11, 1977, St. Louis Park, Minn.—2 elevators destroyed; 1 dead.
- May 25,1977, Logansport, Ind.— heavy damage.
- December 21, 1977, Tupelo, Miss.—2 killed.
- December 22, 1977, Westwego, La.—35 killed (worst since 1908).
- December 27, 1977, Galveston, Texas—18 killed, 21 injured.
- January 21, 1978, Duluth, Minn.—1 injured; damage $1.5 million.
- April 21,1978, North Kansas City, Mo.—1 killed, 35 injured.
Property damage in the last five incidents alone ran high in the millions.
Most of the buildings involved were modern, fire-resistive structures. They were also quite large, which increases the explosion danger in several ways.
Unfortunately, as the locations in the list indicate, these structures are often not protected by major metropolitan fire departments. Smaller communities will more often, however, be the site of the smaller regional elevators. Once known as country elevators, many of the small facilities spotted along branch line railroads in rural areas have been phased out or greatly enlarged in recent years. Although smaller, such elevators, operating the same way as the terminal type, contain the same hazards.
Of cribbed timber or sheet iron on frame construction prior to 1905, grain elevators today are usually concrete. The first all-steel elevator is under construction now at Havre, Mont.
Then why has the elevator blast and fire hazard worsened, notably since 1950? There seem to be four main reasons:
- The way modern elevators are built. Ironically, “fireproof” concrete and steel has actually increased the risk. Besides the familiar fire triangle components, the dust explosion requires a fourth element: confined space. The wooden elevators of the past often suffered little blast damage because their structures would easily “give” to vent an explosion. Fire did the major damage—$54 million from 1883 to 1901.
- Changed grain marketing and storage practices. During the postwar and Cold War eras of the late 1940s and the 1950s, elevators served primarily for long-term surplus storage. Grain might lie undisturbed in bins for years. But beginning in the 1960s, a shift from storage to marketing functions began moving grain in and out much faster.
- More use of pesticides. Such chemicals as Phostoxin are believed to liberate fumes, such as phosphine gas, which increase the likelihood of explosion.
- The maintenance cost squeeze. As in all industry, the first elevator function to suffer from cost-cutting is maintenance. Cleaning, bearing oiling, general inspection—operations, though critical to elevator safety—are too often neglected.
But the modern elevator is “tight.” Though recommended for years by such standards as NFPA 61B and 68, venting is seldom adequate. New environmental restrictions on atmospheric dust have made this situation worse.
Although NFPA codes have recommended a “large percentage” of window area in elevator headhouses and conveyor galleries, this ideal is not common in large elevators today. Also, ordinary glass window panes have been found to withstand blast pressures above design loads for concrete walls.
Besides this tightness, which permits buildup of high internal pressure, elevator headhouses and tanks are bigger than they used to be. The “economy of scale” seen throughout industry has brought greater unit capacities. Modern materials permit structures impractical with wood framing.
It was once thought that heavy concrete elevator design would be strong enough to safely contain an internal explosion. On that basis, the world’s biggest elevator, built in Chicago, was considered so safe that insurance was unnecessary. Yet in 1921 it exploded, killing six persons. The force of the blast shifted 40 300,000-ton loaded concrete silos 6 inches on their foundations.
At this same time, the combine corn harvester was introduced. This brought large amounts of moist, field-shelled corn into storage, requiring artificial drying which made it more brittle. Between 1951 and 1970, U.S. grain production rose 50 percent. More easily broken kernels, plus much larger volumes of grain being handled, meant much more elevator dust.
Grain handling suffers from two special handicaps. One is the small number of employees—normally part-time or seasonal—needed to operate a very large facility. For example, one 5-million bushel midwestern elevator needs only 13 workers during peak periods. A manufacturing plant of similar size would employ hundreds. This means some parts of the elevator may go unseen for days, even weeks, at a time.
The other handicap is the highly competitive nature of grain marketing. In 1972, gross profit of 5 cents per bushel was unusually high for a regional elevator handling 500,000 bushels annually. Quick processing of large volume is essential to recover high capital investment. Careful maintenance doesn’t boost profit— it siphons off one or more of the few productive workers.
Why little is done
In other industries, new technologies are reducing explosion hazards, but such measures are seldom applied to grain elevators.
- Explosion suppression systems, such as those using fluorocarbons, are commercially available and seem effective for spaces up to 1000 cubic feet. However, elevator spaces are often far larger.
- Dust collection equipment, often of limited effectiveness, isn’t widely used. A 1972 survey showed only a third of the elevators so equipped, and more than half the others had no plans to install dust collectors.
- Inerting—use of inert gas atmospheres within elevator structures—was proposed more than 60 years ago. It has proven effective. But it isn’t used in commercial elevators today, it’s claimed, because of the difficulty of sealing structures tightly enough to contain the gas. High cost is also a factor.
- More than 200 elevators have installed dry-pipe sprinklers in headhouses. Their value for fire control is unquestioned, but blast protection is another matter.
One large elevator firm has developed a dust-tight enclosed conveyor with pressurized surroundings so dust cannot escape from any leak. After six years of operation one plant showed no dust buildup. Conventional electrical equipment and wiring was approved in the building. Construction and operating costs were greatly reduced. Such design, however, is not easily adaptable to existing plants.
So much for limitations of existing technology. As one research team put it, “Relatively little advance has been made (since 1940) … in either implementation or improvement of preventive measures.”
Intensive grain dust explosion research is now being undertaken by three groups:
- At least nine universities, prominent among which are Kansas State and the University of Iowa.
- The U. S. Depart ment of Agriculture, in Washington, North Carolina, and at its Graining Marketing Research Center in Manhattan, Kan.
- Grain industry trade associations the National Grain & Feed Association (NGFA), and the Grain Elevator & Processing Society (GEAPS).
But progress is slow, funding uncertain, and any real breakthrough may be long in coming.
Problem being studied
Even before the fatal explosions of December 1977, GEAPS became so concerned that it convened the first international symposium on grain dust explosions at Kansas City October 4-6, 1977. Among the 263 attendees from six nations was K. N. Palmer of Britain’s Fire Research Station, author of the only current book on this subject.
In cooperation with the USDA, the National Research Council in 1978 set up a July 11-12 international meeting on elevator explosions in Washington, D.C. Experts from a dozen countries were invited. Assistant Secretary of Agriculture P. R. Smith said the objective was “to develop a current, informed summary of existing knowledge of the causes of grain elevator explosions, and develop a coordinated research strategy”
Study proposals have been made by the Fire Research Center of the National Bureau of Standards, the National Science Foundation, and other agencies. What is being learned? First, there are some differences between dust explosion behavior and other ignition processes more familiar to fire fighters.
A dusty environment gradually becomes dangerous through cumulative buildup of the dust hazard in contrast to the dispersive nature of gas or vapor hazards. The time interval may be considerable, and if dust can be removed during this interval, no explosion will occur.
It has also been found that there is no such thing as a dangerous dust cloud which remains invisible. Once an explosive concentration exists, the dust particles will almost instantly cluster into visible groupings to create a definite fog in the air. Photocell detectors that respond to visible smoke will also detect grain dust clouds, even below the lower explosive limit (LEL).
Dust on hot surfaces
One of the most prevalent elevator hazards, however, is not dust in the air itself, but the layer of dust on heated surfaces—such as hot bearings, or overheated motors. Once thisngnites explosively, the detonation both scatters more dust into the air and provides the high energy heat source to touch it off. Such dust ignites at temperatures far below the ignition point of LPG or gasoline vapors.
Researchers have found that heated grain dust gives off visible aerosol particles and gases long before the dust reaches its ignition point. These invisible products can be detected in the air by ionization type double-chamber smoke detectors or by combustible gas detectors. The former seem to work best where dust coatings are very thin. Apparently the aerosol particles emitted by the lower layers of dust are absorbed again in the upper layers, but the gas detectors function well with dust up to 732-inch thick.
Preventing dust formation to begin with is another promising field for research. The USDA claims “very significant” effect on dust suppression in lab experiments using a mineral oil spray to coat grain. Animal or vegetable compounds also work. The process would add about 0.1 percent extra weight to the grain, to be allowed for in marketing. This has considerably complicated the whole dust-handling problem. Because the grain weight is reduced by the amount of dust given off during processing, the collected dust must usually be returned to the grain before shipment—intensifying the hazard in later handling.
A Factory Mutual researcher has proposed a fine water fog in certain ele• vator spaces to mix with airborne dust, causing it to be cooled and diluted. He estimates that an elevator handling 40,000 bushels hourly might need only 0.8 gpm of water mist.
A dust control specialist in the midwestern grain industry suggests an “air-washing” system of fans to ventilate the entire dead air space within elevators, thus preventing dust deposit on building surfaces.
All these proposals carry heavy cost penalties. In addition, putting moisture in the grain works against the also costly use of drying facilities to remove the moisture again.
Other studies focus on the nature of the dust itself—how it is produced, the chemical and physical nature of particles, and the effect of process changes on dust generation. Most of this is aimed toward development of monitoring devices to give elevator operators early warning of explosive conditions. One expert visualizes a computerized system having a variety of malfunction detectors. Unfortunately, devices to quickly monitor dust concentration in the air do not yet exist.
It’s estimated that for an elevator of 600,000-bushel capacity handling 6000 bushels per hour, 50 signal points might be needed—in dust cloud areas, around conveyors, at bearings and motors. This could cost from $50,000 to $100,000, just about 3 percent of total elevator cost. If such systems do find wide acceptance, of course, trained manpower must receive—and act on— trouble indications.
Problems and solutions
Wherever these investigations may lead, fire service personnel should be aware of the chief elevator hazards and what can be done today to reduce them. For decades, the problems and solutions have been these:
- Welding or cutting operations. They should be permitted only under the strictest control, in well-ventilated areas, with all machinery idle.
- Poor housekeeping. Keep dusty areas cleaned Up.
- Open flames (especially smoking materials). No smoking rules should be tightly enforced.
- Slipping elevator belts. Adjust tension properly and use slow-down alarms to sense decrease in belt speed due to jamming or overload.
- Hot surfaces (electrical devices, bearings, steam heat pipes). Use overheat alarms; maintain equipment properly.
- Friction sparks from tramp iron or machinery. Use magnetic separators ahead of machinery; check and clean them regularly; prohibit nailed shoes in the elevator.
- Electric arcs from static, cable damage, voltage surges, or wrongly applied electrical equipment. Ground all devices; provide lightning and surge suppressors; use dust-ignition-proof devices.
- Lowering portable lamps into bins. This should never be allowed.
NFPA Standard 6IB, which recognizes these known hazards, has become an American National Standard (ANSI Z12.4-1971), but has not been adopted by OSHA.
OSHA has limited concern
This agency is concerned for the safety of elevator wokers. OSHA has the authority to require elevator dust levels below 15 milligrams per cu ft of air. (About 550 mg/ft3 is a “dense fog.” Recently inspected elevators have shown levels as high as 1900 mg/ft3.) The OSHA limit is set to protect workers’ lungs rather than to prevent explosions.
An OSHA alert was issued, however, early in 1978 after several fatal blasts, and testimony on the explosion problem was taken in March before the House Education & Labor Committee. But OSHA manpower is limited, and some elevators may operate four years without an OSHA inspection. Besides, OSHA normally inspects only in response to complaints or after incidents and has no fire protection code to enforce.
Nonetheless, OSHA has assessed the operator of the Galveston elevator (which exploded December 27, 1977) $116,000 in fines for “willful violations” of safety regulations. These included lack of worker training in dust explosion hazards, use of improper electrical and other equipment for the hazardous area, failure to properly collect dust, and others falling within categories 2,6 and 7 of the foregoing list. A Department of Labor decision is pending on possible criminal court action.
Fire service inspections
Routine fire safety inspections, however, cannot be left up to OSHA. Nor is this the job of the USDA inspectors, who do check those elevators where federal grain inspectors are stationed. Some elevator operators are openly hostile to the USDA and its 1978 safety guidelines.
Fire service inspections should focus on use of properly approved and labeled explosion-proof electrical equipment in all parts of the elevator exposed to grain dust—motors, controls, lighting, and accessories. Look for good maintenance practices. Neglect in the form of heavy layers of dirt, leaking oil or grease, rust, broken parts indicates potential danger. Check for dust collection or ventilation equipment not working. Look for vibration or overheat alarms on all motors, or bearings, and find out whether such alarms are heeded. Do they automatically shut down machinery, or ring a bell, or just light a lamp on a panel which may go unseen?
Ask to see machinery maintenance records. If none exists, the operation isn’t being run properly. Talk to employees as well as to management. Find out if workers have been trained in building evacuation and in the importance of dust cleanup. Determine if they know what can cause dust explosions.
Some grain industry people are very knowledgeable in these areas. The NGFA has urged all its members to take action against hazardous conditions and to train its workers.
Here are some sources for further information on grain dust explosions— causes, prevention and research:
- Cooperative Extension Service, Shellenberger Hall, Kansas State University, Manhattan, Kan. 66506, offers for $50 a comprehensive educational package on dust explosion and fire prevention. It includes 80 slides and accompanying tape cassettes.
- GEAPS, P. O. Box 15024, Commerce Station, Minneapolis, Minn. 55415, offers for $25 the complete printed proceedings of the 1977 international symposium on grain dust explosions.
- Energy & Mineral Resources Research Institute (R. Jnsen S. Hansen, director), Iowa State University, Ames, Iowa 50011, has a 119-Page “Literature Survey of Dust Explosions in Grain Handling Facilities: Causes and Prevention,” written in March 1976.
Until the research pays off, and until dust explosions are more thoroughly understood than they are today after 100 years of occurrence, grain elevators will remain a serious hazard. Realizing the nature of the problem is the first step toward controlling it.