Surge Pile Accident Prevention
Avoiding surge pile accidents requires a combination of good safety practices and effective training of surge pile workers. The following measures represent current best practices for safe surge pile operations. These measures have been arrived at by studying surge pile accidents and by compiling ideas that are now in use at various surge pile operations. They are presented here so that the ideas can be shared with mine operators. If these practices are followed, fatalities from surge pile accidents could be eliminated.
1. PROVIDE EQUIPMENT CABS STRONG ENOUGH TO RESIST BURIAL PRESSURE, OR USE REMOTE-CONTROL EQUIPMENT.
The prime purpose of surge pile safety measures is to prevent equipment from becoming buried in a surge pile. However, the mobile equipment used on the piles should be equipped with fully-enclosed cabs designed to allow the operator to be rescued in the event an accident does occur. This means that the cab must be able to withstand being buried in the pile. This is needed to provide a backup margin of safety in the event that a breakdown occurs in the normal safety procedures. An alternative approach would be to use remote-control equipment.
In most fatal surge pile accidents, it has been found that the coal broke in the cab windows and filled the cab. Based on the accident history, it appears that the cab windows should be strong enough to resist being buried in at least 35 feet of coal. For a density of 80 pounds per cubic foot, this corresponds to a pressure of about 20 psi.
The windows of dozer cabs can be made to withstand burial pressure by a combination of installing supports for the glass, improving the edge support for the glass, and using high-strength window material, such as chemically-strengthened glass. An adequate factor of safety should be provided on the window strength to account for possible variations in conditions.
A common accident scenario is for a bulldozer to fall backwards into a hidden void when bridged-over material collapses. In these cases, structural damage can occur to the cab from the impact. If the existing roll-over-protection structure would not protect the rear window and cab in this situation, then to help absorb the impact, additional structural protection should be installed behind the cab.
As an alternative to providing a cab strong enough to resist burial pressure, technology is now available to allow the use of remote-control equipment on surge piles. This approach would remove the operator from the potential hazards of operating on the pile.
2. EQUIP THE CAB TO ALLOW A RESCUE IN THE EVENT OF AN ACCIDENT.
Provide self rescuers, radio communication and lighting so that the operator can be rescued in the event of an accident. Equipment should only be operated on surge piles with the doors and windows closed to prevent the entry of coal into the cab in the event of an accident. Equipment operators should wear their seatbelts at all times while operating on the pile in case the equipment would suddenly roll or fall into a hidden cavity. "High back chairs" should be used to help protect the operator from neck and head injuries, should the equipment fall backward into a void. Door latches need to be properly maintained to help ensure that the doors do not come open from the impact of falling into a void. The radio antenna should be mounted where it would not be damaged in the event of an accident. Some mines are providing chemical lights in the cabs as a backup lighting measure.
A surge pile rescue plan should be prepared which addresses who will be notified and what equipment will be used in the event of a surge pile accident. One self-rescuer can last up to 4 hours, depending on how efficiently the person uses the oxygen. At least two rescuers should be supplied to allow time to dig out the equipment.
3. PROVIDE THE MOBILE EQUIPMENT OPERATOR WITH THE CAPABILITY TO SHUT DOWN THE FEEDER AND STACKER BELT FROM THE CAB.
This capability can be provided by a radio control that is located in the cab and activated by the operator pressing a button. Some radio-control systems are also capable of continuous transmission monitoring where a warning is provided if the signal is interrupted. This provides an excellent way for a control room, or plant operator, to be signaled in the event equipment becomes buried. The loss of signal can also automatically shut down the feeders and belts. A tilt switchcan also be used to automatically shut down the feeders and belts if the equipment rolls or falls backward. In the event of an accident, the capability to quickly shut off the feeders and belts would help minimize the burial depth of the equipment.
4. PROVIDE GATES ON FEEDERS SO THAT COAL CANNOT DISCHARGE WHEN THE FEEDER IS NOT ACTIVATED.
To ensure that coal feeds only when intended, feeders should have gates which are closed when the feeder is not being used to draw coal. In some cases, coal has fed through ungated vibratory feeders even when the feeders were not activated. This can create a dangerous condition because an equipment operator would not suspect that a cavity would form over a feeder that had not been activated.
Gates should be provided unless it can be clearly shown that the design of the feeder precludes the possibility of gravity feeding. Such an evaluation should consider the possible variation in the size and properties of the feed material and the condition of the feeder. If gates are not provided based on the feeder design precluding gravity feeding, checks should still be made on a regular basis to verify that material is not feeding from non-active feeders while the belt is running.
5. PROVIDE A MEANS FOR THE FEEDER OPERATOR TO DIRECTLY OBSERVE THE CONDITIONS AND ACTIVITIES ON THE TOP OF THE SURGE PILE.
The person who controls the feeders should be able to observe the top of the surge pile to be able to ensure that coal is feeding properly when a feeder is activated. This is needed so that the feeder operator has a direct and immediate way of telling whether a bridged-over condition develops. If a feeder is activated and the feeder operator doesn't see the coal being drawn into the feeder when and where it should be, then the operator should activate a signal, such as a flashing red light above that feeder, and verbally warn equipment operators of the danger. Closed-circuit television should be used to provide the feeder operator with visual coverage of the pile whenever the top of the pile cannot be directly seen from the feeder control room.
A second reason for having the feeder operator be able to see the pile is to allow that person to periodically make a visual check of the safety of the equipment operators on the pile, as well as ensure that no one is in the area of a feeder when it is to be activated.
Some operations monitor the weight of the material on the belt as a way to be warned if a cavity develops. The combination of being able to see the top of the pile and monitor the weight of material on the belt, would allow the feeder operator to detect and provide timely warning of the development of dangerous bridging conditions.
6. MARK THE FEEDER LOCATIONS.
The location of feeders should be clearly marked, such as by using large markers or lights suspended directly above the feeder locations. A high-powered light shining down on the feeder location would be effective for nighttime operations. Where pile height can vary significantly, a pulley system could be used to allow the height of the markers to be adjusted with the pile height.
7. PROVIDE VISUAL INDICATORS OF WHICH FEEDERS ARE OPERATING.
There should be visual indicators to show the mobile equipment operators which feeders are being used to draw coal. Preferably, a system of lights is used such as using a yellow light to indicate when the feeder is activated, a blue light to indicate that the feeder is not operating, and a flashing red light to warn of the potential for a cavity above the feeder.
8. AVOID OPERATING EQUIPMENT OVER THE FEEDERS.
Many of the accidents have occurred when a bulldozer fell into a hidden void while pushing coal away from the stacker. Operating equipment over a feeder both promotes bridging by compacting the surface of the pile and exposes the operator to the potential hazard of a hidden cavity. With the feeder locations marked, the pile should be operated, to the extent possible, in a manner such that equipment does not pass over a feeder.
When operating over feeders equipped with gates, take the following steps:
1. Operate the feeder and verify that coal is feeding properly into the feeder;
2. Close the feeder door and physically tag and lock it out;
3. Fill in the drawoff cone.
After completing this verification process, the feeder can be traveled over as long as the gate remains physically locked and tagged.
9. CONSIDER MOBILE EQUIPMENT SAFETY IN THE DESIGN OF NEW SURGE PILE FACILITIES.
Whenever new surge pile facilities are constructed, the design should include features to minimize the potential hazards to mobile equipment operators. In particular, measures to eliminate or at least minimize the need to travel near feeders when pushing coal away from the stackers should be incorporated.
10. USE SAFE PRACTICES WHEN PUSHING TO A DRAWHOLE.
When pushing material to a drawhole, equipment operators should always operate facing and directly toward the feeder location. Since the edge of the drawhole is unstable, operators should never backup near, or operate along the edge of, a drawhole.
The higher the pile is, the larger the diameter of the drawoff cone. To assist equipment operators, markers can be placed on the stacker tubes to indicate the height of the coal and a chart can be prepared, using the typical angle of withdrawal of the material, to provide operators with guidance on how far back from the feeder they should stay for a given height of pile. This chart can also be used by equipment operators to provide guidance on how close to a feeder they can come when a cavity is suspected over the feeder.
If coal is feeding properly and a normal cone of depression is being created, then material can be pushed to the edge of the drawhole. However, a condition can develop where only a relatively small hole opens up over the drawpoint. This may indicate that the coal is feeding down a "chimney" about the drawpoint, or what appears to be a chimney could actually be a small opening over the center of a large cavity. A dozer operator could be endangered by pushing coal all the way to this hole because if the hole is an opening at the top of a large cavity, then the weight of the dozer could collapse the cavity. If coal is not feeding in a conical shaped drawhole, then a cavity should be suspected and the condition should be immediately investigated and corrected by digging in from the side of the pile.
11. KEEP THE DRAWHOLE NEARLY FULL DURING LOAD OUT OPERATIONS.
During load-out operations, the capacity of the equipment pushing to the drawholes should be matched to the load-out rate so that the drawholes can be kept fairly full. This is safer than having to push to the edge of a deep drawhole. It is a good practice for dozers to be positioned in a safe place on the pile when load-out operations begin. This allows the equipment operators to observe whether the material feeds properly.
12. PROHIBIT PERSONS FROM WALKING ON A SURGE PILE.
Persons should be prohibited from walking on a surge pile unless appropriate safety precautions, such as the use of safety lines, are taken. Equipment operators should be instructed not get off of their equipment while it is on a surge pile. A particular concern is for the safety of persons, such as maintenance or contractor personnel, who may not normally work around the pile and may not be familiar with the dangers. Ensure that such persons are trained about the dangers. Post warning signs around the surge pile to identify the danger area and reinforce the training information.
13. OPERATE SAFELY AT NIGHT OR UNDER CONDITIONS OF POOR VISIBILITY.
Adequate illumination should be provided for operations after dark. Work with the mobile equipment operators to determine where best to install lighting to minimize glare problems. Water vapor coming off the coal can make visibility difficult or impossible. The use of infrared cameras may be useful in these types of situations. When visibility is inadequate the operation of mobile equipment should be suspended until conditions permit adequate visibility.
14. PROVIDE FOR COMMUNICATIONS.
There should be provisions for radio communication between everyone who either works on the pile, affects the pile, or supervises pile operations.
15. COMMUNICATE WHEN A CAVITY IS SUSPECTED.
If a cavity is suspected, the condition should be immediately reported to all employees in the affected area and to the supervisor in charge of stockpiling operations. Cavities should be eliminated immediately or the area should be dangered-off. A warning signal such as a blinking red light above the feeder should be used to indicate to everyone that a potential cavity exists and that no one should go near that feeder.
16. USE SAFE PROCEDURES TO ELIMINATE A CAVITY.
Cavities need to be eliminated by a method which doesn't expose the workers to a hazard. Measures such as the use of high pressure air or water should be used from the reclaim tunnel where possible. If such measures are not successful, then the cavity should be eliminated by excavating into the pile. This activity should be under the direction of a supervisor and should be started a safe distance off to the side of the pile and away from other feeders. In performing this work, material needs to be removed from low enough on the pile that the cavity is broken into on the side, rather than near the top where the operator could be endangered. Use of a long-reach excavator should be considered.
17. PROVIDE ADEQUATE HAZARD TRAINING FOR ALL SURGE PILE WORKERS.
All employees who work on surge piles need to be trained on surge pile hazards. Hazard training also needs to be provided for anyone who might only occasionally do work associated with the pile, such as maintenance personnel or contractors.