In early January 2006, a methane explosion tore through a coal mine in Sago, West Virginia, trapping 13 miners nearly 100 meters underground. Cut off from communicating with the miners, authorities could not determine where they were—or even if they were still alive. By the time rescuers reached the miners 2 days later, all but one had died.
After the incident, Gary Smith, a retired engineer, sent a letter to his ex-manager at the Lockheed Martin Corp. in Syracuse, New York. Smith, who grew up in a West Virginia mining family, asked his former colleagues if anyone knew of a technology that could provide reliable communications during such disasters. After reading reports of the Sago incident and discussing similar emergencies with federal mine safety officials, the Lockheed Martin engineers updated a very old one.
The team focused on a concept developed over a century ago by Nikola Tesla. The noted pioneer in electricity and radio had shown that a magnetic wave generator could be used for wireless communications.
Basically, the generator works like an electromagnet. Powered by standard alternating current or battery, it runs electricity through a wire that is coiled around a metal cylinder, creating a harmless, low-energy magnetic field that extends for hundreds of meters. Just like radio, the field can carry an audio signal by modulating (raising or lowering) its strength instant by instant. But unlike radio, cell phones, and satellite phones—whose electromagnetic waves can't pass very far through rock, clay, or other materials that conduct electricity—a magnetically generated signal penetrates the ground easily. On the other end, a coiled antenna wire about 100 meters long receives the signal, and an amplifier converts it into sound.
In the 1890s, Tesla experimented with the concept as a possible alternative to Marconi's wireless telegraph. But the device's relatively short range and high signal noise made it impractical for widespread use. Short range is not a problem in most mine situations, explains engineer David LeVan, who led the Lockheed Martin research team. The devices the group developed, called the MagneLink Magnetic Communication System, combine a refrigerator-size magnetic generator with a briefcase-size receiving antenna. One such unit operates on the surface; the other, down in the mine. LeVan says tests earlier this year at a mine in Mavisdale, Virginia, showed that the low-frequency signal can penetrate through 500 meters of solid rock, making it usable in more than 85% of underground mines in the United States.
The team solved the problem of signal noise with the same type of digital signal-processing software used in cellular phones, LeVan says. The software also allows users to send and receive text messages. Although the units are rather bulky, they fit easily next to miners' emergency shelters with other lifesaving equipment. The underground transmission antenna is wrapped around one of the coal pillars that help to support the roof of the mine tunnel. A box made of polycarbonate (photo, in foreground) houses the receiving antenna.
Each generating unit can operate at least 24 hours on 12-volt battery power, which complies with U.S. Mine Safety and Health Administration (MSHA) requirements, and contains a telephone handset and text-message pad. Its low energy output means it poses no danger of sparking, which could set off an explosion if methane gas is present.
MagneLink program manager Warren Gross says that during field tests, miners offered many suggestions for making the units simpler to operate in emergencies. It's important, he says, that users need only turn the unit on, pick up the phone, and talk or text. Gross says the company is awaiting MSHA certification. If the agency approves the system, he says the units should start rolling off the assembly line by the end of this year.
Todd Moore, the director of safety services for CONSOL Energy, a coal-mining company in Canonsburg, Pennsylvania, says he has been advocating for this technology ever since the Sago disaster, which involved another coal company. "No one can predict what will be destroyed" in an explosion, says Moore, a lifelong mining safety engineer who assisted in the Sago rescue effort. "Our coal mines are the size of downtown Manhattan." Moore, who has supervised MagneLink tests but was not involved in the research, envisions each mine being equipped with at least several underground units, while topside units move around as necessary. "I am truly convinced [it] can save lives in the coal industry," he says.