Wireless mesh solution sought for mine safety

Federal officials believe wireless mesh networking technology could provide a much-needed safety line for miners working in underground coal mines.

The Health and Human Services Department proposes using mesh technology to provide two-way communications between miners underground and people on the surface. Such a link would be especially valuable in the event of mining accidents in which access to the surface is blocked.

Several fatal mining accidents in recent years resulted from the unavailability of communications during rescue operations. An explosion at a coal mine in Sago, W.Va., killed 12 miners in January 2006. Two more miners died later that month in an accident at the Aracoma Alma Mine in Melville, W.Va. Another explosion in May claimed the lives of five more miners at the Darby Mine No. 1 in Holmes Mill, Ky.

In response, Congress recently passed the Miner Improvement and New Emergency Response Act of 2006, which includes a provision developing a two-way wireless communications system within three years.

The challenge is that communications underground are generally limited in the best conditions and often are lost altogether during emergencies.

"The tragic events at the Darby, Alma and Sago coal mines have highlighted the need for reliable communications between miners inside and outside the mine," according to a request for proposals released Nov. 20. "Present wire-based communications systems may fail due to exposure to fires, roof falls or explosions tearing down wires, power failure or battery failure."

Wireless mesh networks potentially could avoid a lot of those problems. Being wireless, the network infrastructure does not depend on physical lines that can be easily cut. The network lacks a single point of failure and other limitations of traditional client-server networks.

Instead, each user device serves as a node that can help route data to its final destination. That means no individual loss of a node will bring down the network, because data is easily rerouted. Also, users can extend mesh networks simply by adding more nodes.

In most cases, mining operations do not have two-way communications between miners underground and those on the surface, said Luke Popovich, a spokesman for the National Mining Association. Current systems enable people on the surface to send text messages to miners below, but "one of the problems is the devices don't allow for replies," he said.

The mining environment makes it tough to develop good communication systems. The deeper the mine, the more difficult it is to build a reliable network, and the coal mines of Appalachia run deep and under rough terrain, Popovich said.

Federal officials are asking for feedback from industry about whether mesh technology offers a major leap forward for mine safety. One question, of course, is whether the technology could indeed survive catastrophic events, such as cave-ins and explosions.

But officials also wonder how far down a mesh network could run inside a mine, given its unique geometry. "Mines tend to be very long tunnels or [a] series of interconnected tunnels with workers and equipment established along the lines of the tunnel," the RFP states. "This tends to limit the number of wireless mesh devices that can actually 'see' each other, thereby obviating many of the inherent benefits of a mesh topology."

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