When Utah’s Crandall Canyon Mine suffered a collapse in August 2007, rescuers raced to reach six miners trapped inside — and Tunnel Radio of America worked along with them. A communications systems integrator, Tunnel Radio quickly built the infrastructure for an underground radio system. Workers used it as they cleared a path through the rubble into the interior.
“That way, our rescuers had communications as they were moving into the mine,” said Terry Stringham, an RF technician with Windriver Wireless, a Kenwood USA dealer in Roosevelt, Utah, that works with Tunnel Radio. Windriver sent down a dozen handheld radios, providing communications between the people operating the heavy machinery and others bringing in equipment behind them.
Unfortunately, that rescue effort ended in tragedy: a second collapse killed three rescue workers and injured six others.
The Miner Act of 2006 requires that each underground mine in the U.S. implement two separate, redundant systems to provide communications in the event of an accident. In response, vendors have been offering, and the Mine Safety Health Administration (MSHA) has been testing, various systems based on newer technologies such as mesh networking and voice-over-IP (VoIP) telephony.
But two-way land mobile radios also are an option, and they’re already playing many important roles in underground mines, both for everyday operations and for emergencies. Surprisingly, although LMRs are common tools in many heavy industries, not all mines use them.
“Around this area, I really don’t know anyone other than us that does use them,” said Jay Toney, superintendent of the Sunrise Coal Company in Carlisle, Ind. Sunrise has employed radios underground for about 10 years.
Mine radios are gaining ground, however. For example, Lauttamus Communications in Wierton, W. Va., is providing more than 1300 Kenwood radios to Console Energy for its mines, said Paul Lauttamus, the radio dealer’s vice president. “We’re, right now, at the ground floor of this. It’s a market that’s evolving as we speak,” he said.
One reason radios haven’t become ubiquitous in mines is that an underground tunnel system creates a hostile environment for radio signals. “It becomes like an RF tomb,” said Joe Watts, land mobile radio product manager for Kenwood USA. “There’s a lot of energy absorption, reflection, cancellation. The deeper the radio waves go, the more attenuated they become.”
To propagate a signal in a mine, Tunnel Radio and several other companies manufacture leaky feeder cable systems made of coaxial cables with cuts in the shielding that allow radio signals to seep in and out. Strung along the interior of a mine, the cable provides communications with subscriber units. “You can usually get 500 to 600 feet away from the cable before you’ll start hearing it [the signal] degrade,” Stringham said.
Probably the biggest operational use for radios in an underground coal mine is coordinating activities at the face, where miners actually cut the cut coal. “Pretty much everyone up there has a radio on them,” Toney said. Day-to-day safety is another big reason to use radios — for example, for a miner who trips and falls while working alone. “He can get on the radio and say, ‘Hey, I think I’ve sprained my ankle, somebody come help me,’” he said.
Radios also provide communications with the surface. If it looks as though a problem is developing underground, people there can convey that information to people above ground, who can make corrections, pull people out or reassure the miners that they have the situation under control. “You’ve got a lot better look at what’s going on in that mine,” Stringham said.
The only radios that can operate legally in underground mines in the U.S. are those that have passed an extensive MSHA safety certification process. Since 2006, Kenwood’s TK-290 and TK-390 handheld radios have been the only MSHA-approved subscriber units. Motorola used to make an MSHA-approved radio, the HT-1000, but it stopped selling that product in 2004. A new Motorola product, the HT-750, is currently going through the MSHA approval process.
Not just radios, but all machines and devices that operate underground in mines must receive approval from MSHA. The goal of the approval process is to make sure no equipment is brought into a mine that might ignite dust or gases in the environment.
The approval process is long and arduous. “You have to send in all kinds of engineering-level documents,” said Joel Berger, a compliance engineer with Kenwood USA’s research and development organization. For example, MSHA needs to see schematics, printed circuit board views and a bill of materials with component values and tolerances — “everything that an engineer would need to characterize that device,” he said.
MSHA’s engineers closely examine these documents and compare them with sample radios and parts, inspecting and testing every component, Berger said. They need to determine that the radio will not trigger a fire or explosion under any circumstance. “If, for instance, the battery comes off a radio and it’s in ‘transmit,’ drawing its maximum amount of power, the spark that might occur would not have enough energy to torch off that gaseous mixture in its most volatile state,” he said. Along the way, examiners can ask the manufacturer for additional information and samples.
“They really do what you might say at first glance are some pretty outlandish tests. But they can’t take the chance of finding out the hard way. So they’re very diligent,” Berger said. “We’ve spent a lot of time on the phone during the test process, for questions and answers and requests for more information.”
In theory, MSHA could complete the inspections and tests in six weeks, but six to nine months is a more realistic estimate given all the work the test lab has to complete with its small staff, Berger said.
Motorola temporarily dropped out of the U.S. mine radio market because winning MSHA approval was not an early priority for the HT-750, said Paul Cizek, the company’s director of professional commercial radio operations, North America. Motorola first put its efforts into engineering the radio to meet other demands within the three major vertical markets for this product — the mining, petroleum and chemical industries — around the world. Those efforts included meeting the standards for safe operation set by other regulatory bodies such as ATEX in Europe and the Canadian Standards Association.
“It takes years to distribute the platform across all of these needs,” Cizek said. With other certifications obtained, MSHA approval recently rose to the top of the priority list. Once Motorola refined the product to meet MSHA’s standards, it submitted the radio for certification, he said.
It’s difficult to say how long it will take MSHA to complete its evaluations and tests, but approval probably isn’t far off, Cizek said. “This summer, we should have product available,” he said.
Whichever brand of radio is used, a mine may have other options besides a leaky feeder cable system to make those units function underground. Along with its radio system, Sunrise Coal operates a mine page phone system — a hardwired network of telephones with loudspeakers. The vendor, Mine Safe Electronics, offers an interface between that system and radios.
“I can be underground and talk on my radio on a certain channel, and it will page these mine phones throughout the mine,” Toney said. Piggybacking the radio signal on the telephone network also allows a user underground and one on the surface to talk radio-to-radio. “It might be 2 miles, 3 miles, 4 miles … below the surface. I can pretty much get hold of anybody,” he said.
Mine page phone systems, sometimes called squawk boxes, have been around since the 1940s, Stringham said. They work, but if a miner is working too far from one of the wall-mounted boxes, he might not hear the message coming through the speaker. When a miner carries a handheld radio, he doesn’t miss a message, he said, adding that “if an emergency comes up, it’s a quick way to broadcast to everybody in that mine, ‘We’ve got a problem and it’s time to leave.’”
Before the 2007 collapse, the Crandall Canyon mine had only a squawk box system, and employees there didn’t see any need for radios, Stringham said. Having radios available during the rescue operation spurred a big change in attitude, he said.
“They’ve seen what a tool the radio network can be,” Stringham said, “not only in an emergency, but in your day-to-day operations.”
|Mine Radio Systems||Flexcom Communications Systems|
|Varis Mine Technology||Model IS Leaky Feeder Communication System|
|DAC||Type RFM 2000 Radio System|
|EL-EQUIP||Model VHF-1 Radio System|
|Tunnel Radio of America||Model UltraComm Distributed Antenna Communication System|
|Becker Electronics (PTY)||Becker Leaky Feeder System|
|Source: Mine Safety and Health Administration|
|VHF or UHF portable radio|
|Venture Design Services||Model TMLT Text Messaging Location Transponder||Tracking tag and text-messaging device|
|Source: Mine Safety and Health Administration|