You're in my personal bubble

One government organization is taking the basic proximity detection systems available and advancing it to protect the operator and the continuous mining machine.

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The bigger they are…the more they hurt when they hit you. 

Mining equipment is huge, dauntingly so at times. And while their bulky exteriors protect the operator from the rugged terrain and falling objects, they also cause blind spots and limited maneuverability—major contributing factors to mine vehicle related collisions and other accidents.

Also, operator attention and fatigue must be considered, too. Repeated job functions become automatic for operators and mine workers, potentially causing poor decisions. Fatigue may cause an operator to see a hazard but not respond to it, and a warning from a proximity detection system could “wake up” the operator.

The mining industry and regulatory agencies are trialing collision proximity detection and collision avoidance systems as a promising means to protect workers at surface and underground mines with the goal to reduce the number of accidents and fatalities related to the use of this equipment. Currently, for example, the West Virginia Mine Safety Technology Task Force is pushing legislation to make proximity detection systems a part of underground coal mining systems.

One piece of equipment that has received particular attention is the continuous mining machine, which is used in underground coal and nonmetal mines. There are three systems the Mine Safety and Health Administration (MSHA, located in Arlington, VA) has approved. The three proximity detection systems will disable the movement of the continuous mining machine in the event of a ‘danger zone’ breach by a human. And there is a new technology development from The National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research. This new technology development that is on the horizon not only protects an operator in a more intelligent way, but protects the machine from frequent start-ups by shutting down only specific machine functions on the machine instead of the entire machine, allowing work to continue sooner. This protects components from excess wear due to frequent startups and more importantly, reduces the occurrence of nuisance alarms that could lower confidence in the system.

Approximately 95% of the continuous mining machines are remote controlled, and most remote controlled continuous mining machines (RCCMs) do not have an operator's compartment, according to MSHA. The RCCM operator controls the machine using a remote control unit that directs movement and other functions of the machine. The remote control unit communicates with the RCCM using radio waves or a cable.

While proximity warning detection systems and collision avoidance systems are not new technology, their use in underground mining applications is new. Between 2002 and 2006, MSHA conducted tests of this technology in collaboration with proximity detection manufacturers and mine operators at mine sites.

NIOSH has been conducting research on proximity detection technologies independently since the mid 1990s. The technologies ranged in type from radio to radar to infrared to electromagnetic field based systems. NIOSH found that many of the technologies tested worked well for surface mining applications, and after MSHA reviewed the technologies, it was determined that electromagnetic field based systems offered the greatest potential for underground.

According to NIOSH research:

A significant number of mining accidents are attributable to powered haulage equipment collisions, loss of control, and pinning-related accidents. More than 40% of the most serious injuries (fatalities and permanent disabilities) in the mining industry involve accidents classified as struck-by or caught-in machinery and powered haulage equipment. The most common activities associated with these incidents were maintenance and operating the machine.

According to Mine Safety and Health Administration (MSHA) accident data, from 2002-2008 the coal industry averaged 1,206 accidents per year involving mobile face equipment. Of these, 252 per year occurred while operating continuous mining machines.

In informal discussions, continuous mining machine manufacturers and machine operators have both expressed concerns about increased incidents while tramming equipment.

Recently, proximity detection systems have been emerging in the mining industry as a useful tool to predict and prevent collisions between one piece of mobile equipment and another, or between a piece of mobile equipment and a person.

Manufacturers have developed several types of systems using various technologies for this purpose. Some of the technologies utilized in surface mining and other industries include the Global Positioning System (GPS), and radar-, laser- or ultrasonic-based distance sensors.

Unfortunately, these technologies are ineffective in the underground mining environment, where GPS is unavailable, dust, water and other harsh conditions interfere with measurements, and the close proximity of mine walls would cause frequent false alarms. In this environment, electromagnetic proximity systems are a common solution.

Electromagnetic field systems consist of two components: an electromagnetic field generator and field detecting devices. Both of these components of the system can be worn by the operator or installed on the machine. The system can be preprogrammed with a defined ‘danger zone’ that, when entered by the operator or other mine workers, can provide a warning, stop the equipment (or a function of the equipment) or both.

MSHA approved systems

Currently, there are three MSHA approved systems for underground coal mines: Frederick Mining Controls’ HazardAvert System, Nautilus Intl.’s Coal-Buddy System, and the Matrix Design Group’s M3-1000 Proximity Monitoring System.

The HazardAvert proximity detection and collision avoidance safety system by Frederick Mining Controls LLC, Huntsville, AL, emits an audible and visual warning alert and can be programmed to slow or stop the machine automatically when the predetermined ‘danger zone’ is breached. (For coal mining applications, the system’s components are housed in MSHA rated explosion proof enclosures, and are specifically designed to endure the continuous duty cycles of the mining environment.)

HazardAvert creates a magnetic marker field around machinery using a field generator installed on the machine. The generator creates low-frequency electromagnetic signals to mark areas considered to be potentially hazardous; low-frequency signals pass through almost anything, including coal, rock, dust and water. The marker field can encompass the entire machine and its turning radius, or be specific to certain areas.

Workers and operators wear a Personal- Alarm Device (PAD) that detects and measures the magnetic marker field to determine their proximity to the machine and alert them of possible danger to their safety. HazardAvert is currently installed and operational in underground coal mines in South Africa, and is supported by the Australian Coal Association Research Program and a number of coal and hard rock mines in Australia. Furthermore, a unique version of its hardware is being supplied to NIOSH to assist in the testing of an intelligent proximity detection system.

Single generators integrated into a piece of equipment can define a zone that covers the machine and its turning radius; for larger and more complex zone shapes, multiple generators can be used on the same machine. ‘Silent zones’ – or areas within a determined danger zone that allow operators to work – can be added inside the marker field to allow operators to function in specified areas close to the machine without activating the alarm or disabling the machine.

The Matrix Miner Monitor M3-1000 provides a practical, mine-duty system that trains operators to remain clear of unsafe areas, or "red zones," by warnings and machine shut-downs. A recent partnership between the Matrix Design Group LLC (Matrix) of Newburgh, IN, and Joy Mining Machinery, Warrendale, PA, has allowed the M3-1000 system to be operationally tested on a Joy 14CM15 continuous mining machine in production use in a Western Kentucky coal mine. The system is anticipated to be commercially available in the U.S. market in early 2011.

July of this year, ARLP announced that several of its independent operating subsidiaries had begun deploying a Matrix designed proximity detection system. At the time of the announcement, operating companies had installed seven proximity detection systems on continuous mining machines in production at five underground coal mines.

Nautilus Intl., Burnaby, British Colombia, Canada, designed its Buddy Proximity Detection System to train mine workers and equipment operators on what distance is safe to maintain from a continuous mining machine. It is being used every day in production in Massey Energy and ICG (International Coal Group) mines in the USA.

A fast one-midnight-shift installation time is average for a complete Coal Buddy System. The system features two small, intrinsically safe MF4 antennas that are installed on the continuous mining machine and radiate two magnetic fields around the complete machine. The strengths of these magnetic fields are measured by the operator's Proximity Detection Device (PDD); if an operator gets too close to the continuous miner, the PDD warns him, and if he enters ‘the Red Zone’ that is the predetermined dangerous proximity, the continuous mining machine is automatically disabled.

The PDD carried by the operator weighs only 0.43 lbs. (0.19kg). The electronic circuit board inside the battery pack measures the distance between the operator and the approaching machine. If it gets too close, the operator will be warned; if no action is taken by the operator, the CM will be stopped.

The PDD has an 'Override Warning' touch pad on top, which can allow the operator to get very close to the CM without shutting it down, providing he keeps his thumb on the touch pad all the time.  If he lets go of the touch pad even for a split second when the CM is too close then it will immediately be shut down.

Avoiding machine shut-down

The NIOSH Office of Mining Safety and Health Research (OMSHR) is developing an intelligent proximity detection and warning system for underground miners and machine operators that does not shut down the entire vehicle.

In the past, “typical proximity warning products have shut down the equipment, and then you have start up time,” says Chad Hutson of NIOSH. Start up times can be longer for certain equipment that must have its systems checked before the machine can start working again, and constant shut downs are hard on equipment and components, especially diesel-operated systems.

NIOSH’s newly developed proximity detection system doesn’t shut down the entire machine, it only disables specific machine functions. So, dangerous machine movements are prevented, but safe movements are allowed, which means mining can continue with limited interruption.

The system has been a culmination of years of research by NIOSH looking to how to make things safer for mining machine operators. “We’ve done a lot of small research projects up to this point to determine, first and foremost, how many injuries there are related to continuous mining machines, which we found was roughly 240 injuries per year and an average of 1.2 fatalities per year related to continuous mining machines,” says Chris Jobes, research engineer for NIOSH.

“We conducted interviews to determine why miners stand where they do, what they are trying to see, and where around the mining machine they are being injured,” Jobes says. “We also did some motion analysis on operator ‘escapability’ to find out why those locations are hazardous. We know there is a mining machine and we know that it is big and is in an enclosed area, but why can’t the operators get away from the machine?”

The motion analysis was conducted on various operators and included three postures, eight escape directions, and three operator facing directions—looking over their left shoulder, right shoulder and straight ahead.

The analysis gave data on the operators’ actual motions so the motion could be incorporated into a simulation complete with a simulated mining machine. This allowed different escapability scenarios to be studied quickly and without danger to test subjects. 

There were definitely a lot of variables:

For example, “If they are in X location facing Y direction in Z posture, and they escape in direction A, and the mining machine is rotating in direction B, and they are C distance from the machine, what is the probability they will be struck by the machine?

“We did 14,000 simulations, and out of those 14,000 simulations there were roughly 10,000 times in which the simulated miner got struck,” says Jobes.

The simulations allowed NIOSH researchers to establish how far an operator should stand from a continuous mining machine to be considered safe. It was discovered, too, that it wasn’t the speed of the machine causing the injury, but rather how close the operator was standing to the machine.

“The operator has to stand close to the machine in order to see what he needs to and to operate the machine effectively. He has to stand far enough away from the machine to be able to be safe. But, if he stands too far away from the machine, he could be put into harm’s way by other pieces of equipment such as a shuttle car,” Jobes says. “Farther isn’t always better, but there has to be some sort of safe location.”

It was here that NIOSH decided that specific functions of the machine would be controlled based on a control system’s knowledge of the exact location of the operator in relation to the machine, causing a function shut down, not an entire machine shut down.

To do that, the onboard computer had to be aware, through sensor measurement, of the locations and actions based on controlled commands, and its current movement of the various machine parts. It also has to know where the operator is in the moment, and finally the machine has to have a controller. The computer can then use pre-programmed logic to allow it to make intelligent decisions based on the current position of the operator, the machine position and action command by the operator, as to whether the action will be allowed or not.

The system consists of four magnetic field generators with control systems on the continuous mining machine that will be sequenced to send out a magnetic pulse at a specific frequency. The operator and other miners that will be in close proximity to the machine will each have a Personal Alarm Device (PAD) which acts as a magnetic field sensor that senses the strength of the magnetic field and wirelessly sends the reading back to the onboard control systems controller to determine the operator’s distance from each generator. As long as two of the generators have readings, a GPS-like triangulation algorithm can pinpoint the operator’s location in relation to the machine.

The distance from the machine will determine whether the operator is in a safe or dangerous zone. Dependent on the zone, an action will be determined to be allowed or not allowed. “We’re not shutting down the machine, we’re just disallowing certain activities of the machine until the people move or the situation changes,” explains Jobes. As an example, Jobes explains what could happen if the operator were standing dangerously close to the tail of the machine. “Instead of shutting down the entire machine so everything has to get reset and restarted, it’s ‘The tail won’t move over, so I have to move so the machine will allow me to move the tail where I want it to be.’”

The software was created by NIOSH, but the physical hardware is a variation of the aforementioned existing system supplied by Frederick Mining Controls plus some added sensor hardware and a more powerful onboard computer.

“Theoretically it can be applied to any piece of mining equipment. There may be issues with having multiple machines equipped with the magnetic field generators causing problems with synchronizing generator pulses. In that case you may have a problem implementing this solution mine-wide, but in theory it can be applied independently to any individual machine,” Jobes says.

Future work

Moving forward with the project, NIOSH would like to put more generators around the machine to cover the entire machine with safety zones. 

Also, the posture of the operator and other miners around the machine could provide valuable information. “If we know the posture the operator is in, we can also determine things like how much notice the operator needs to escape. If he’s squatting or kneeling, escape may be more problematic than if he’s standing. Given that, we may be able to adjust the warning system accordingly,” Jobes says.