 Stalking is an integral part of most coal mining operations. Stockpiles provide storage for raw and clean coal. Raw coal is stored to provide a steady supply of material for the preparation plant and clean coal is stored to provide a sufficient supply to meet customer demands. Coal may be stored in enclosed facilities, such as the silo shown here. It may be stored in open stockpiles where it is recovered from draw off points located beneath the pile, or the coal may simply be piled on the ground where it is recovered by loading it out from the toe or base of the pile. Stockpiles are, by their very nature, potentially dangerous structures upon which to work. The material is stored in a relatively loose condition, but moisture freezing within the stockpile and the compaction of mobile equipment operating on it will sometimes allow the stockpile slope to stand at a steep angle. But in this condition the material is only marginally stable because any temporary strength due to moisture or freezing may be lost as weather conditions change. Safety problems may also be aggravated when some mines exceed the original designed capacity of storage facilities because of production demands or lack of space for additional storage piles. This leads to construction of higher stockpiles and the increased use of mobile equipment operating directly on top of the stockpile material. Surge piles that have materials being removed by underground feeders can be particularly dangerous. The main reasons for this are, one, material feeding into the draw point will not support weight and will act like quicksand, two, material around the edge of the draw hole is weak and marginally stable, and three, there's the possibility of material bridging over the draw point causing a hidden void. A model of a surge pile and miniature toys representing mine personnel and equipment will be used to demonstrate what happens inside piles that can create hazardous conditions for personnel working on them. The coal used in this model has been layered with sand to increase the visual effectiveness of the demonstration. Draw holes are formed when the feeder underneath the pile draws off the material from above. As material flows down through the feeder opening, a cone-shaped zone and draw hole is formed above the draw point. If a person or piece of equipment is on the pile within this zone when the feeder is activated, the flowing material will not support the weight, and when the cone-shaped zone widens, the equipment and operator are pulled into the hole. Part 77 of the Code of Federal Regulations, section 77.209 states, no person shall be permitted to walk or stand immediately above a reclaiming area or any other area at or near a surge or storage pile where the reclaiming operation may expose him to a hazard. Another reason why surge piles are hazardous to work on is the possibility of material bridging or arching over the draw point and creating a void just above the feeder opening. This can be extremely dangerous because the void cannot be detected from the surface. Different mining accident records show that the majority of coal stockpile accidents have occurred when a dozer was driven over a bridged area of a stockpile and the area suddenly collapsed burying the machine and the operator. To better illustrate how bridged material can fail under the weight of mobile equipment or personnel, let us return to our model. Here we see a bridged condition that could have resulted from fines and moisture that caused the material to cake and adhere together making it less free-flowing or it might have been caused by freezing where moisture and ice bonds the material near the surface preventing it from flowing freely. This creates a frozen crust-like area or bridge of material having high temporary strength. At the same time, the material deeper within the pile below the bridge does not freeze and may continue to flow thereby causing a void or cavity to form above the draw point. To emphasize just how unstable and dangerous bridge formations and voids in surge piles are to operators of mobile equipment, we will demonstrate what can happen when equipment is driven onto a stockpile and over bridged material. The bridged material may have enough strength to support its own weight but it may not support the weight of a piece of equipment or even a person especially when it has been weakened due to thawing or sprawling underneath. Heavy mobile equipment operating directly on a stockpile can contribute to bridging problems. The weight and vibration of this dozer moving over the surface tends to compact the material immediately below it. Continued packing of the material helps form the bridge and the creation of a void below the bridge as the looser material above the draw point continues to flow into the feeder. Production of material near the surface of a stockpile may also result from material that is dumped from a conveyor and as the pile gets higher the weight of the material itself increases the compaction. To help equipment operators and others involved in stockpiling operations avoid the dangers of bridged materials, hidden voids and weak material and quicksand like conditions around draw holes it's important to identify the location of the draw points, the location of the feeders under the pile and to determine which feeders are operating. Some minds suspend indicators or markers from cables directly above the feeders to identify their location. These indicators may be brightly colored markers, lights or other highly visible objects that will help guide operators to safely position their equipment during stockpiling operations. These operators should also be given a chart that indicates the safe operating distances from the center of the feeders or from the unstable areas such as draw holes that are formed by the cone shaped zones above the feeders. These measurements are based on the pile height and the angle of the material. To avoid getting too close to the draw hole it is extremely important for mobile equipment operators and other workers on stockpiles to know which feeders are operating. They must also be aware that some feeders are automatically controlled or programmed to begin discharging when another draw point runs empty. Everyone involved in stockpiling operations should know which feeders are being used and who is working on the pile. Before starting a feeder plant operators must be certain by visual inspection or other positive means of communication that no one will be endangered. Reliable communication between plant personnel and equipment operators is essential. A two way radio is an effective direct method of communication between the feeder operator and dozer operators on the stockpile. Many potential problems can be eliminated with the use of such equipment. Other effective methods for communicating which feeders are in operation include a series of indicator lights that can be readily seen by the equipment operators. These may light up or blink when the feeder is activated. These monitoring devices were designed to alert equipment operators of feed material activity and the possible presence of a bridge formation and void above the discharge point. As an added precaution workers should always suspect that there is a hidden void over each feeder because a void can develop any time that a feeder might be activated. A mobile equipment operator who works directly on the pile should communicate with an assigned person periodically on a regular time cycle to keep other employees aware of their condition that they are safe. Time intervals between communication should be fairly frequent not to exceed 30 minutes. Failure to receive communication from an equipment operator must be investigated immediately to determine the cause of the delay. The on shift foreman should always try to maintain close and frequent communication with the equipment operators. As stated under federal regulations no employee shall be assigned or allowed to work alone in any area where hazardous conditions exist unless they can communicate with others can be heard or can be seen. When stockpile activities are in progress all employees should be trained to keep an eye on operations whenever possible. The monitoring of equipment operators or pedestrians on or around stockpiles can be done in various ways depending on location and visible accessibility. If the control panel operator's station is located where he or she can keep invisible contact this should be encouraged. Another effective means of monitoring stockpiles employs video cameras strategically placed to record or view appropriate areas. These monitors allow for continuous viewing of the operations and are not affected by weather conditions and human error. At many mines stockpiling operations are performed at night or during dark, overcast and dismal weather conditions. Adequate lighting must be provided on mobile equipment and stationary installations to illuminate the working areas of the pile. Area lighting that illuminates equipment in stockpiles should be installed in such a way or angle that it reduces glare into the operator's cab. Also spotlights installed directly over the draw off points would provide additional illumination and more importantly would help mobile equipment operators identify the danger areas at night. Operators should be in place on top of the stockpile early in the loading process and during the entire operation. In this way they can keep the draw down area and reclaim holes full of material which will allow them to observe the material as it feeds into the draw point and to better know what areas of the pile are safe to operate on. Because of the limited field of view from the dozer cab and the danger of collapse of the edge of the draw hole, operators shouldn't push material directly into the hole. Instead, it should be bumped in with the next blade of material. This will allow the dozer to maintain a safe distance from the edge. Also, the dozer should always be operated perpendicular to or straight toward the edge of the draw hole. This gives the operator more time to back up should a slope failure occur or if the material starts to settle. And finally, the dozer should always operate facing the draw hole to prevent accidentally backing into the hole. Operators of stockpiling equipment should always wear seat belts. Operators show that operators not wearing seat belts who are involved in stockpile accidents are more likely to be injured by striking interior parts of the vehicle or be killed if thrown out and by the equipment rolling over them than they would by being engulfed in loose material and suffocating. All mobile equipment that operates on a surge pile should be equipped with a fully enclosed cab. Other safety features include strong window mountings and high strength window material or guards that will maintain their integrity should the equipment become buried. The need for further development and implementation of methods and materials to improve cab integrity and safety such as altering the window mounting and using an aviation type safety glass has been brought to the attention of equipment manufacturers and mine operators. Dozer cabs should be provided with one or more self-contained self-rescuers. The number required can be determined by the estimated time needed to recover an operator and equipment if they were drawn into a surge pile and covered with material. Operators thoroughly trained in using an SCSR may substantially enhance their chance for survival if they are trapped inside a cab which is buried under material. Using the SCSR breathing apparatus could keep them alive and give the rescue team additional time to reach them. It is also recommended that enclosed cab stockpiling equipment be provided with an operable interior light to allow the operator to don his SCSR. If the equipment does happen to be drawn into a hole, operators should stay in their cabs. If they jump, they will very likely be pulled into the loose material and would then be buried by the material and die from suffocation. If you are involved in an accident where your cab is covered by material, stay in the cab, shut off the equipment's engine, and if a two-way radio is available, try to call for help. When the cab is completely covered, you'll need to put on your breathing apparatus and remain inside the cab until rescuers reach you. Every company that uses mobile equipment for stockpiling operations should have a rescue and recovery plan in case of a stockpile accident. Such plans will be site-specific and formulated by the company for their particular operation and they should include these two basic elements. One, information regarding the location and availability of equipment that could be used to dig out specific pieces of equipment that may be buried in a stockpile accident. And two, a listing of readily available emergency medical services and rescue recovery equipment and personnel. All rescue and recovery plans should include the designation of a person or persons to be responsible and in charge of recovery activity. And the methods of organization and implementation of this plan should be incorporated into the company's safety training program. Another hazardous situation connected with surge pile operation can occur if a feeder becomes clogged or blocked. The concern is that when trying to get the material flowing again, miners will be exposed to hazardous conditions from unstable material above or below them or from flowing material once the obstruction is free. For example, miners standing on top of a pile, possibly above a bridged opening, sometimes fail to understand or even think of the possibility that the stockpiled material they are trying to free is also the material which is supporting them. Some storage facilities may be equipped with accessory units such as vibrators which are designed to break up any bridges or blockage. If they fail to free the blockage, then it may be necessary to excavate into the pile to break loose the material. This is a potentially dangerous job that must be performed carefully with trained personnel. Material should be removed while working from a safe area to the side of the pile so that equipment and personnel are not exposed to the hazard of breaking into a void. The material must also be removed in such a manner that no steep slopes or overhangs are created. Whenever dealing with clearing blocked feeders or making repairs, the feeders should be shut off, locked out and tagged. Only trained personnel should be authorized to perform these operations. Sometimes coal is stored by simply dumping it on the ground, using conveyors or trucks and dozers. There are no draw off points, so it's usually reclaimed from the pile with front end loaders that remove the coal from the toe or base of the slope. In such open type stockpiles without draw off points, the hazards are somewhat different from surge piles, but the dangers of loose, marginally stable materials still remain. Most of the accidents that occur on these types of stockpiles are due to haulage trucks or other mobile equipment going over the edge of the slope. Such accidents have occurred due to brake failure, lack of an adequate berm, the driver misjudging the edge, or the collapse of the edge of the stockpile. Loading out at the toe sometimes causes over-steepening of the slope. The edge of the slope then becomes marginally stable and may collapse under the additional vehicle weight, which in the case of a loaded haulage truck can be a very significant factor. Other accidents such as material falling onto operators and their equipment at the base of the stockpile can also occur due to over-steepened slopes. Loading out at the toe operations also presents a hazard to those on foot at the base of the pile, particularly truck or loader operators who may be engulfed by falling material while walking between their equipment and the pile. These people must be trained to avoid these areas. The hazards of operating at the base of the pile increases significantly as the stockpile height increases, especially when the pile becomes higher than the reach of the loader. When this occurs, there is more danger of over-steepening or undercutting the pile. A good safety rule is for the loader not to work into the toe of a pile which is higher than the reach of the loader bucket. This limitation will enable the loader operator to safely trim down steep or over-hanging material and will restrict the amount of material which could be involved in a slide or slope failure. When a stockpile has become over-steepened from being loaded out, material should be bumped over the top of the pile and worked down until the slope reaches its angle of repose. Loader operators should keep their equipment nearly perpendicular to, pointed straight toward the slope. This will help keep the operator's compartment farther away from potential slides. And if the slope is frozen, operators must be aware of the danger of ice binding the material causing the slope to form an overhang or stand at a steep angle. Then when the thawing occurs, the material may collapse without warning. The dumping of additional material on a pile and reclaiming material from the toe of the pile should be coordinated so that equipment is not dumping on top of the pile near the area where material is being loaded out from the toe of the slope. When operating equipment on top of stockpiles, certain safety practices should be followed to avoid potentially hazardous conditions. Haulage trucks should dump the material back from the edge of the pile. A good rule of thumb is one truck length back from the edge. If it must be pushed over the edge, let a dozer push or bump it over. The equipment operators should travel at reduced speeds when backing toward the edge of a slope and then bring their vehicle to a gradual stop. An abrupt stop near the edge imparts an additional force on the slope material which can cause the collapse of a marginally stable slope. Burms provide a visual indicator of the location of the slope edge. And although they may be capable of offering resistance to the passage of equipment, a typical axle height berm is not normally capable of stopping a large truck and should not be relied on to do so. Also, the presence of a berm does not necessarily mean that it is safe to back up all the way to the berm and dump because the slope may have been undercut on the other side during loadout operations. At some dumping points, such as unloading into hoppers, solid permanent type berms or stop blocks are used. Operators of mobile equipment that work on or around stockpiles must be trained to recognize potential hazards that are inherent in such structures as cracks along the crest of the pile, slumping on the slope, bulging at the toe, material sloughing and other signs of slope instability. They must correct or report these dangerous and impending conditions and they must avoid traveling on suspect areas. Stockpiling techniques vary depending upon the size of the mine, the type of material handled and type of equipment available. Some techniques are safer than others and should be used when applicable. But safe operation of mobile equipment is largely dependent upon the competence, skill and experience of the equipment operators. Their ability to quickly react to a potential hazard during stockpiling operations not only affects their own safety, but also that of their fellow workers. But in the final analysis, safety is the responsibility of every employee, from the equipment operator to the mine management. It is only with the active participation and cooperation of everyone involved that the occurrence of stockpile accidents can be reduced or eliminated and a safe work environment can be assured.