Calling for better mine safety

Communications technology in many underground mines is primitive, consisting of phones and handsets connected by wire. It works, but it's vulnerable. If an accident severs the line, the system fails, and miners lose contact with people above ground. If it's a dangerous accident, one that leaves people trapped underground, the loss of communications can be deadly.

In the wake of multiple fatal mining accidents, Congress passed a law in 2006 that requires better communications and miner-tracking systems. But developing new technology for tough underground conditions has been demanding, particularly with the law’s tight three-year time frame for fielding a system.

“By government contract perspectives, we had to move at light speed,” said David Snyder, a senior mine electrical engineer at the National Institute for Occupational Safety and Health’s Office of Mine Safety and Health Research.

To meet the goals of the law, called the Mine Improvement and New Emergency Response, or MINER Act, NIOSH officials worked closely with L-3 Communications and other industry partners. A collaborative relationship was critical to keep the project on schedule, particularly because the requirements were vague.

“The MINER Act wasn’t an engineering document, so there were a lot of things that were left for interpretation that ultimately will be interpreted by the Mine Safety and Health Administration,” Snyder said.

For example, the MINER Act states that communications must work after an accident occurs, but it doesn’t say for how long. It also requires the ability to electronically track where people are in a mine, but it doesn’t say with what precision.

Snyder said the ambiguity created trade-offs and system design options that the agency had to evaluate with the help of its development partners.

For its part, L-3 pulled together a team that included Virginia Tech’s Department of Mining and Minerals Engineering and a company called Innovative Wireless Technologies, which provided the wireless solution.

A critical goal of the project was to create a redundant system that would be capable of surviving an emergency. The challenges included limited power and radio range underground and restricted paths into mines for a backup system.

Project leaders originally planned to use a wireless technology called ultra-wideband that was in development for the Defense Advanced Research Projects Agency. It doesn’t require much power or a dedicated frequency, and it can provide location-tracking capabilities. However, developers determined it didn’t work well underground.

“We morphed our original thinking into a mesh solution, and we found 900 MHz to be the ultimate frequency to propagate in a mine. It is the sweet spot,” said Vic Young, who directs L-3’s mine safety programs but used to work in the company’s military communications division.

With a traditional wireless network, fixed base stations communicate with mobile nodes, such as radio handsets, but the system is vulnerable if those base stations go down.

In a mesh system, fixed mesh nodes with backup batteries allow for dynamic routing of communications so that the loss of any particular node does not take the whole system down. In addition, the miner radios also act as nodes for the network, providing further system resiliency. The radio handsets can also communicate with one another independent of the network.

L-3 installed a pilot system in International Coal Group, Wolf Run Mining Company's Sentinel mine near Philippi, W.Va., in October 2008.

The system, called Accolade, consists of a network of mesh nodes that extend from the mine’s surface through an elevator shaft and a portal to one of the working sections underground. The network provides untethered voice and text communications and miner location tracking through handsets that each miner carries.

The system tracks miners by measuring which node is receiving the strongest signal from the handset. A situational awareness display at the surface provides a mine map showing miners' locations. The map data is also available via the Web.

“The biggest benefit of the wireless system is being able to communicate from anywhere in the travel ways,” said Chuck Dunbar, director of acquisitions and planning for International Coal Group. “You don’t have to go find a wired mine phone to talk to the outside or to the working sections.”

In the future, the International Coal Group hopes the ability to communicate wirelessly from an active section of a mine will lead to safety and productivity improvements, such as safety inspections, supply requests, and other maintenance and timekeeping reports.

Officials say the system could also work in other applications, such as underground mass transit systems.