FIREFIGHTING HAZARDS AT GRAIN FACILITIES
Responders to emergencies at grain-handling and storage facilities must be knowledgeable about the operations, machinery layout, entries and exits, and potential hazards of these facilities. Grain-handling facilities present unique firefighting hazards for responders. The risk of fires in such facilities, while not particularly high, is always present; and minor incidents have the potential to become major disasters.
COMMON FIRE HAZARDS
Some of the areas/equipment and potential fire hazards common to grain-handling/storage facilities are discussed below.
Dust Explosion
A dust explosion can cause great devastation and loss of life. It usually occurs in enclosed equipment, such as the bucket-elevating leg, or in enclosed areas, such as bins or silos. For a dust explosion to occur, it must have fuel, oxygen, an ignition source, and confinement. Since it is virtually impossible to control oxygen and confinement in most facilities, prevention of explosions is centered around controlling ignition sources and removing fuel (dust).
Bearing failures and frictional heat from slipping belts and hot work such as welding and cutting are the primary sources of ignition.
The majority of grain dust explosions occur as a small primary explosion followed by one or more larger, secondary explosions; the latter usually cause the most casualties and property damage. Secondary explosions can occur when layered dust on beams or ledges becomes dislodged and placed in suspension, creating an explosive concentration. A flame front, emanating from equipment ruptured by the primary explosion, can serve as an ignition source for the secondary explosions. These explosions cease when the fuel is consumed or explosive pressures have been vented.
Dust explosions cause great structural damage. Responders could be endangered by the falling of large pieces of concrete and structural steel. Responders must be extremely cautious when operating in and around the heavily damaged structure. Operations will involve rescuing trapped workers and containing any fires resulting from the explosions. Decisions as to whether to place personnel in the structure should be carefully thought through and should be based on the probable locations of known missing workers and the likelihood of their having survived the explosion.
Grain Dryers
Many of these facilities have grain cleaning/screening equipment and dryers, usually located outside the facility. Grain dryers, which reduce the moisture content of grain to enhance its storabilitv. usually are fueled by natural gas. propane, or fuel oil. They usually are equipped with automatic shutoff mechanisms to prevent overheating; some also may be equipped with a separate power source for their emergency dump system. Upper areas of dryers have minimal clearance and are difficult to reach.
A common cause of dryer malfunction is plugged grain flow, which can result in a dryer fire or the conveying of smoldering grain to a storage bin. Most grain dryer fires are caused by improper operation and can be extinguished routinely by on-site personnel following the proper procedures. Severe dryer fires, however, require professional response.
Responders first should shut down fuel to burners and the dryer, shut down grain flow into the dryer, and discontinue all grain flow into the facility. If you cannot manually remove the burning material, activate the emergency dump system or run the grain out on the discharge rolls, where the fire can be extinguished w ith hoselines. If the burning material cannot be moved from the dryer, use hose streams on the exterior of the dryer or gently apply water through the screens. Check receiving bins, conveyors, and other relevant areas for spread of hot material. Hot grain should not be conveyed into the facility. After the fire is extinguished. the dryer should be thoroughly emptied and cleaned.
Bucket Elevators
A fire in a bucket elevator is difficult to fight. Should fire, smoke, or heat be present in the bucket elevator leg. stop grain flow into the leg and shut down the leg, if it hasn’t already been done. Never run burning grain through a bucket elevator; grain flow w ithin the elevator can generate significant amounts of airborne dust, increasing the probability of explosion. (Some bucket elevators are equipped with dust-control systems that remove dust and convey it to a holding bin.) If possible, limit openings in the leg casing, and shut gates to reduce air flow.
Fire or heated areas may be found by touching the casing (enclosure around the buckets) or looking for discoloration. When found, cool the heated areas from outside with water. Once the casing is cooled, gradually open the inspection door close to the suspected fire area, and apply water at a low flow rate. Feel the door before opening it; stand to the side and stay low when actually opening it. Extinguish fires gently inside the leg casing, using small-diameter hose under low pressure. Do not disturb layered dust.
After the fire has been extinguished, completely wet the boot section, since material may have fallen down the leg. Then check for potential fire spread in the bins or conveyors that were receiving grain from the leg.
Ignition sources in bucket elevators may include friction occurring between a pulley and belting or resulting from the rubbing or striking of the bucket or belting against the casing, a malfunctioning bearing, and friction caused by foreign objects.
Bucket elevators also contain numerous combustibles, in addition to grain and dust, including the plastic buckets, rubber or PVC belts, spout lining, and bearing lubricants.
Galleries and Tunnels
Galleries and tunnels may be equipped with horizontal conveyer belts or drag conveyors. which move the grain. Fires in these areas may result from malfunctioning bearings; friction occurring between a belt and its frame, a belt and its casing, or a belt and pulley; or burning material on a conveyor.
Bins and Flat Storage
Grain stored in bins or warehouses also represents a potential fire hazard. The causes of bin fires include the entrance of smoldering grain into the bin, the ignition of grain by an external heat source such as hot work or a light bulb; and spontaneous combustion resulting from out-of-condition grain, which can produce enough organic heat to reach the ignition temperatures.
Bin fires, because of their location, cannot be easily reached by conventional firefighting methods and may not be immediately detected.
Concrete bin fires. A grain or dust fire in a concrete bin or silo is most difficult to extinguish. Rarely will significant flame be present; therefore, the fire may not be easily located or may not be detected by temperature cables. Firefighters should consider using tools such as thermographic photography and thermometer probes to locate hot spots. The following factors must be known before attempting to size up a bin fire:
- contents of the bin.
- presence of fumigants or chemicals,
- proximity of the bin to other structures.
- structural loading of the bin. and
- areas to which hot grain can be diverted.
Applying water is the most common approach to fighting concrete bin fires. However, there is a potential hazard associated with this approach: The water could react with carbon to form a potentially explosive concentration of carbon monoxide and hydrogen known as “water gas.” If water is used, apply it at a very low flow rate and only where necessary. Gently wet down interior exposed walls at the bin top and grain surface, using probes or access holes to apply the water.
A different approach is to control the fire by removing its oxygen supply. Sealing the bin and injecting carbon dioxide or nitrogen from the bottom is one way to accomplish this. Regardless of which method is used, be extremely careful that you do not stir up dust on the walls or on the top of the grain, and never try to fight a fire from inside the bin. Monitor temperatures in adjoining bins throughout the operations. And, as always, shut down equipment operating in the area before beginning extinguishment efforts.
If the bin fire cannot be extinguished, consider removing the smoldering grain, f irst, wet down the exposed bin bottom in the tunnel and surrounding equipment. Unload the material directly outside through manhole ports or loadoul spouts by auger or other means. Slowly allow the grain to drop onto the floor in the tunnel. This can be accomplished using a temporary chute or by cutting or removing the belt, allowing the grain to flow directly onto the floor. If it is not possible to direct the grain flow directly onto the floor, allow it to flow onto the stationary belt. As the materials exit the bin, they should be wetted down. Never run hot or burning grain from a burning bin through an elevator leg or into another bin.
Preferably, use doors or other bin openings before resorting to cutting a hole in the structure. If cutting is required and the structural loading has been reviewed, consider consulting an engineer to ensure the integrity of the bin. Then, position hoselines and clear equipment and debris from the area before cutting. Strategically locate and size the holes so that walls are not weakened, and be prepared for material to flow out. Do not remove reinforcing rods.
Steel Tank Fires
Fighting fires in steel tanks involves unloading the tanks or, in the case of small tanks, using atmosphere inertion. First, stop all equipment operating in the area, particularly the aeration system, and conveyors to and from the tank. If the tank is small, seal the bin to limit oxygen. You may consider injecting carbon dioxide or nitrogen. In large structures, open doors to accommodate manual unloading technique.
Before removing grain from the bin. wet down the surrounding area and equipment. Never run hot or burning grain from a burning tank through an elevator leg or into another tank. Isolate the fire by selectively unloading the grain—that is, remove the grain located near the fire until the burned grain is detected. Once detected, slowly allow the smoldering grain to flow from the tank, wetting it as it exits. If the fire is confined to small areas and entry is required, use protective equipment, life-support lines, and proper confined space techniques.
As you would with concrete bins, use existing openings to provide access before cutting the tank. If you must cut. consider installing slide gates to control the flow of grain exiting the tank. Also, have the areas checked or evaluated by a structural engineer. When selecting areas to be cut, avoid structural supports, studs, and electrical wiring.
Once an area has been approved for cutting, outline the cuts to be made by drilling intermittent holes. Using a metalcutting power saw, cut the metal along its studding to provide stability and ease of repair. Periodically cool the blade and area being cut by applying water. The entire sheet or panel that is cut should be removed.
Hazardous Materials
Pesticides, fumigants, dryer fuels, gasoline or diesel fuel, lubricants, and cleaning solvents are among the hazardous materials stored at grain-handling facilities. Identification of the hazardous materials involved is very important. Some fumigants (such as those generating phosphine) can react rapidly in the presence of moisture, causing exothermic heat and explosive gases or fires. Your response to releases and/or fire involvement of such materials should be within the parameters of the OSHA 1910.120 standard, your department’s standard operating procedures, and any other safety procedure or standard required by the authority having jurisdiction.
Electrical Equipment
Transformers generally are located outside facilities. Relays and circuit-control devices may be located in a totally enclosed motor control center, separate from the rest of the facility. These areas may be kept under positive air pressure to minimize dust accumulation.
Wiring (normally in conduit) runs throughout the facility. Electrical components are dust-tight for Class II, Division 2, Group G locations. In extremely dusty areas, electrical components meet Class II, Division I, Group G specifications. The use of “classified” electrical equipment in grain-handling facilities has greatly reduced electrical equipment’s potential as an ignition source.
Bearing Fires
Fires ignited by bearing malfunction may involve burning dust, grease, or oil and thus should be smothered. Bearings at the head (top) and boot (bottom) of a bucket elevator are most likely to malfunction and overheat. If fire occurs in a bearing located outside equipment, cool the bearing and hot surfaces with water. Bearing fires located inside equipment are more difficult to fight. Stop grain flow immediately. Then, using a fog nozzle, gently direct water toward the bearing. Use extreme caution when opening closed equipment.
Conveyor Belt Fires
These fires may occur as a result of friction between the belt and frame or the belt and pulley, from an overheated bearing, or from burning material on the belt. Even flame-retardant or self-extinguishing materials can burn.
To control a belt conveyor fire, stop the grain feed and conveyor, if it hasn’t already been done. If the conveyor is enclosed, close the discharge gates. Next, locate hot spots by looking for discolored metal. After locating hot spots, gently cool the casing with water or an extinguisher.
You may decide to cut the conveyor belt to isolate the fire. Nevertheless, apply water or use an extinguisher gently. Do not cause any layered dust to become airborne. Also check for fire in the bins or conveyors that were receiving grain from the conveyor. Note: Black smoke may indicate burning plastic, rubber, grease, or the presence of toxic vapors or gases.
Each grain-handling facility is unique in layout, design, construction, operations, equipment, and personnel. Each facility, therefore, warrants individual emergency preplanning and firefighting procedures. Such plans should be a mutual effort between the management of the facility and the fire department.
Note: The information in this article was gathered from various reports and publications published by the National Grain and Feed Association, which has published an excellent pamphlet, titled “Emergency Planning and Firefighting Manual, ” that is a must for firefighters with grain-handling facilities in their districts. An accompanying video, titled “Partners for Protection, ” is also available through the NGFA, 1201 New York Avenue NW, Suite 830, Washington, DC 20005.
