By Steve Fiscor, Editor-in-Chief

The Affinity mine recently installed proximity detection on all of its continuous miners and haulage units.

While most underground accidents are avoidable, proximity detection represents a significant technological leap forward in accident prevention. West Virginia recently made proximity detection a priority (See News, p. 8) and the Mine Safety and Health Administration (MSHA) has also identified it as a best practice.

Since January 1, 2010, 85 U.S. coal miners have been injured by mobile equipment (including eight miners who were killed in accidents involving mobile face equipment). One of those fatalities occurred at the Affinity mine, located in Sophia, West Virginia, and operated by a subsidiary of United Coal. It was a tragic turn of events for a company that had overcome several challenges while it rehabilitated a mine and built an operation with four super sections.

United Coal invested a considerable amount of time evaluating various protection systems for mobile equipment and committed the resources to install a permissible mine-wide proximity detection system at its Affinity mine. The system they selected was the HazardAvert proximity system, which is marketed by Strata Products Worldwide. The trial use of the system on a Highland Machinery shuttle car and a Fairchild 35C DC-powered scoop demonstrated to MSHA and United Coal that the system was scalable. All of the continuous miners and powered haulage at Affinity are now equipped with proximity detection — with positive results. The company now plans to install the system at all of its mines.

The system forces miners to develop a better awareness of their surroundings. “Miners have to be conscious of where they are,” said Ed Toppings, United Coal’s vice president of maintenance. “The shuttle cars look ahead 15 ft. Even if miners are in a cross section, the field might still pick them up and slow the shuttle car down. Scoops can travel anywhere so they really have to be aware of the travel-ways. They used to make sure they were out of the roadway and now they have to move farther out of the way to avoid detection, which is a good thing.”

When the system was first installed, the reception was less than enthusiastic. However, attitudes have changed. “One of the miner operators, a fairly outspoken opponent to the system, recently admitted that since the installation, he realized he had developed some bad habits,” said Barry Elliott, maintenance superintendent for Affinity. Toppings acknowledged that “training, open lines of communication with our workforce and experience using the system have helped us turn the corner.”

An operator stands in the safe zone, which is more than 15 ft from the field generator mounted on the tail of the continuous miner.
An operator stands in the safe zone, which is more than 15 ft from the field generator mounted on the tail of the continuous miner.

How the System Works
The Affinity mine operates two 10-hour production shifts per day and employs about 200 miners. On average, it produces 10,000 raw tons of metallurgical-grade coal per day. Like most underground mines in West Virginia, the operating conditions are tight. The roof is 56 in. in the high zones and the seam undulates. The visibility is limited for shuttle car and scoop operators especially when rounding corners or passing through check curtains. Proximity detection helps eliminate those blind spots.

Strata’s proximity detection system is based on electromagnetic (EM) technology. Each piece of mining machinery is equipped with four EM field generators, typically located on the four corners of the frame. The proximity detection system overlaps the four fields to create a shaped field around the machine that is suitable for underground mining equipment. The end result is an elliptical-shaped static field that is narrow on the sides and projects farther in front and behind the machine.

The field generators emit a low frequency pulse. “At that frequency, we have very stable fields,” said Mike Berube, COO, Strata Safety Systems. “That frequency minimizes parasitic coupling characteristics.” Parasitic coupling occurs when metal, such as chain mesh, draws a portion of the EM field toward it.

Strata’s shaped fields are repeatable and static. The miners wear a Personal Alarm Device (PAD), which is about the size of a cap lamp battery. Oddly enough, with so many mines opting for cordless cap lamps, it fits perfectly where the battery was on the mine belt.

The PAD contains ferritic coils mounted on a 3-D axis. If the miner is standing up, laying down, or moving in an unusual manner, the coils will still sense the EM pulse and determine its strength. Strata sets predetermined levels for multiple warning zones. Affinity has a warning zone set at 15 ft and a danger zone stop at 5 ft.

That PAD will recognize the strength of the pulse and alert the miners with audio and visual alarms if they enter a warning or danger zone. A radio frequency (RF) link from that PAD in the 900-MHz range transmits back to the machine alerting it that miners are in its warning zone. When the miner steps into the danger zone, another signal stops the machine. A relay, which is hooked to the hydraulics, flips open and stops the movement of the machine.

The Strata system can handle multiple miners working in a warning zone all day. Intermittent beeping can be heard as miners and machinery interact and, should one of the miners set foot inside the danger zone, the machine will stop.

What really sets the Strata system apart from other systems, according to Berube, is the system’s ability to handle multiple machines and miners in close proximity. “Our system has the architecture to handle a PAD in the warning zone of a continuous miner with a shuttle car approaching,” Berube said. “It will alert the continuous miner that a miner is in the warning zone and it will stop the shuttle because the miner is standing in the shuttle car’s danger zone. That is quite tricky to do and something that we have been working to perfect for six years now.”

The other concept that required a lot of thought was the safest location for the continuous miner operator. “With these shaped fields, the continuous miner operator needs to stand in place where he can mine coal safely, but not be in danger when the shuttle car arrives,” Berube said. “We have spent a lot of time developing the fields so there is the interaction between the continuous miner and the shuttle cars that allows the operator to stand in a safe place, not trigger either machine and still be able to mine coal.”

Berube and his team investigated the use of dynamic fields, but ultimately decided to stick with static fields. Theoretically, as the machine moves faster, the dynamic field would grow larger. “It looked good on paper, but underground it was a constant form of frustration,” Berube said. “We spent a lot of time on this and came full circle. The reasoning is that a miner should be able to approach a shuttle car from section to section and mine to mine, and know where those zones are going to be. Then the miners can be trained on how they can interact with them. It’s just a much more efficient way to engineer proximity detection.”

The Strata system is frankly a simpler system, Berube said. A more complex system has more potential for failure. “When a mine is looking at a safety system, they want the safest system with the least potential critical points for failure,” Berube said. So he and his team invested a great deal of time creating repeatable static zones that are fail-safe.

Strata’s proximity detection system interacts with miners and multiple machines simultaneously.
Strata’s proximity detection system interacts with miners and multiple machines simultaneously.

Installing the Systems Underground
Toppings and Elliott have managed the process from evaluation to operation. The system became fully operational at Affinity during February 2014.

“It’s been a pretty big job installing all of the systems underground,” said Elliott. “We installed the system on four shuttle cars outside, the other 12 shuttle cars, 10 or 12 scoops and eight continuous miners have had the systems installed underground. We have had little or no issues with damaged cables and components. We lost one generator to physical damage and we had another generator that failed because of the motherboard.”

Affinity uses Joy continuous miners, Highland Machinery shuttle cars and Fairchild scoops. “The controllers are a mix of CableForm and Saminco on the scoops,” Elliott said. “When the system activates on the older scoops with Saminco controllers and DC drives, it gives a warning when miners are in the zone and locks the brakes up if a miner is in the danger zone. On the AC scoops, it shuts the pump motor off. The continuous miners react by disabling the traction drive and the boom swing. On the shuttle cars, when a miner enters the warning zone, they automatically drop down to first speed and then they shut down completely when someone enters the danger zone.”

According to Elliott, the installation was not difficult. “The physical installation of the components is time consuming,” he said. “With the first couple of machines, we had to feel our way through it with the kits and the guarding. After the first few machines, the process became routine.”

“There was a lot of wiring, especially on the continuous miners, and it takes a lot of concentration and effort,” Elliott said. “It took about six hours to interface the continuous miner with the system.” All of the wiring was installed underground.

The system has proven to be reliable. “Much of the troubleshooting process dealt mainly with learning how the system works… maybe the PAD wasn’t charged properly or someone was standing in the wrong spot,” Elliott said. “We had a continuous miner operator who was complaining that the shuttle car was staying in low tram. As it turned out, he was following the shuttle car in the warning zone and his PAD was keeping the machine in low tram.”

“The fields are purposely overlapped,” he said. “Two generators have to see each other. That’s a fail-safe. As the generators power up, they see each other. As the field takes shape, the continuous miner sees 5 ft on the sides and about 15 ft to the front. The field is a little more constrained on the back.”

Toppings and his team evaluated other systems, including the Joy Global system, which uses the Matrix proximity detection system. “Both systems are very reliable,” Toppings said. “Ultimately, we selected the Strata system because it’s simple and effective.” Toppings acknowledged that, at the time United Coal was evaluating proximity systems, Joy was moving from one generation to another.

Since installing the system, production at the Affinity mine has not suffered. During early April, it posted a record day of more than 12,000 tons.

A Worthwhile Investment
While installing and debugging the Strata system within six months throughout the Affinity mine is a significant achievement, United Coal recognized that all of its mines will benefit from this state-of-the-art safety technology. “We performed an analysis, looking at fatalities over the last five years, and determined we could make the biggest impact by eliminating danger zone accidents,” said Mike Zervos, president and CEO, United Coal. “We tested cameras and found that visual quality and blind spots are general problems. Shuttle car operators in particular tend to focus on the camera instead of the road. Given our experience with cameras, we are convinced that proximity detection is the best available technology to prevent those accidents.” Zervos estimates that 25% of mine fatalities could be eliminated if that technology were used at all mines.

“We want to be the first coal company to deploy the proximity detection system at all of our mining operations,” Zervos said. “We hope to have all installations completed by July 1. We are working closely with Strata to achieve that goal.”

United Coal will invest $4.5 million to install proximity detection systems at all of its mines. “That cost doesn’t include the initial disruption in production at our mines, which doubles our investment to $9 million,” Zervos said. “Nevertheless, if the system saves one person’s life, then it is worth the investment.”

Getting More Out of the System
Using a new HazardLink system, all of the information recorded by the HazardAvert system will interact seamlessly with Strata’s CommTrac system. Because all equipment interactions are monitored, the system can provide real-time data regarding warning and danger zone entries.

“This is a really important feature,” Berube said. “We view proximity detection as providing safety in two ways. When someone walks into an area that puts them in danger, the machine is shut down immediately. But there is a bigger picture. We can look at this data and say this miner has only stopped the machine twice in eight hours, while another miner has tripped the machine 10 times in a shift. You could potentially have a scenario where the two miners are producing the same amount of coal, but one miners work habits are much better than the other.” That information can be incorporated into a skills assessment program.

Anything that utilizes HazardAvert can be tracked underground. “The mining company can track the equipment as it’s running in real time, which will provide accurate time studies,” Berube explained. “We will have the ability to see how long it takes a shuttle car to tram from the continuous miner to the feeder breaker or how long the cutter-head is turning over the course of a production shift.” All of that data could be used to increase operational efficiency.