15 September 2010—On 5 August, the collapse at a Chilean gold and copper mine left 33 miners trapped in a chamber nearly 700 meters below the surface. They're still down there, while officials coordinate their rescue. As bad as their situation is, it could have been much worse: They could have been mining coal.
The Chilean miners have been able to talk to their families by phone, and video images of the men have been broadcast around the world. But if they'd been in a coal mine, their television debut would likely have been impossible. The slightest spark from electronic equipment can ignite methane gas and coal dust, touching off a deadly explosion.
In the aftermath of a lightning-induced explosion at a West Virginia coal mine in January 2006, everything went wrong for the 13 miners trapped inside. It took rescuers nearly two days to find them. By then, all but one had died—victims of the explosion and subsequent carbon monoxide poisoning. The lone survivor's account highlighted the conspicuous absence of technology for communicating with the surface. "[We] attempted to signal our location to the surface by beating on the mine bolts and plates" with a sledgehammer, said Randal McCloy Jr. after he was rescued. "We never heard a responsive blast or shot from the surface."
The outrage from that accident was heightened by the deaths later that month of two miners who were lost in a haze of thick smoke from an underground blaze. According to David Chirdon, new technology program manager at the U.S. Department of Labor's Mine Safety and Health Administration (MSHA), people began to ask, " 'If we can put a man on the moon, why can't we talk to miners underground?' I always responded to that by reminding people that we could talk to the astronauts across 240 000 miles of empty space, but when they were on the dark side of the moon, that big rock between us and them presented the same challenge as the earth between miners and the surface."
By June 2006, the Mine Improvement and New Emergency Response, or MINER, Act was signed into law by the U.S. Congress. Among its provisions was the creation of the Office of Mine Safety and Health within the National Institute for Occupational Safety and Health (NIOSH). The new office is responsible for spurring the development of mining communications technology. NIOSH was given just three years to commercialize wireless two-way communication and electronic tracking systems.
According to David P. Snyder, senior mine electrical engineer at the newly created NIOSH unit, the team focused its efforts on getting the systems to be, in mining industry parlance, "permissible." A component is permissible when MSHA certifies that its circuits are incapable of releasing enough energy—during normal operation or if they're damaged in an accident—to trigger an explosion by igniting methane gas or coal dust. Among the rigors a component has to withstand is the "two-fault test." Testers at the agency use an electrical schematic of a device to determine the two worst-case faults it could experience. Even when the testers create short circuits at those points, the device must avoid creating an arc.
MSHA is uncompromising about these tests, says Snyder, because "a methane-air mixture requires less than a half millijoule of energy to ignite." Consequently, a miner trapped underground is going to be severely limited in the amount of power he can transmit.