Fiber optic cable capable of surviving the harsh conditions encountered in underground mines is crucial to the
performance of a rock burst monitoring system at U.S. Silver & Gold’s deep Galena mine in northern Idaho, USA.

U.S. Silver & Gold’s Galena mine, located in Wallace, Idaho, USA, is a 5,800-ft-deep (1,767-m) silver-copperlead mine that produces approximately 900 tons of ore daily. The mine has had consistent seismic activity since the late 1950s. Fiber optic cable from Optical Cable Corp. (OCC) has helped the mine monitor and manage these seismologic changes, resulting in zero deaths or injuries related to rock bursts since 2001.

The Galena mine’s original installation consisted of OCC B-series Mine Safety and Health Administration-rated deployable mining cables. The 6-strand fiber optic cable, installed to a vertical depth of 4,600 ft (1,400 m), served as part of a seismic monitoring system. At the time, it was believed to be the world’s tallest vertical mine cable installation.

“Prior to the OCC cable installation, the Galena mine had one of the more advanced monitoring systems for its time, but it was dependent on manual processing from the underground office,” said Kathryn Dehn, senior rock mechanics engineer. “Today, real time monitoring of seismic activity in the mine allows us to alert workers if a problem is detected, so we can pull them out of an area until the rock stabilizes. It has helped reduce injuries and prevent accidents.”

Dehn said prior to 1992, seismic activity was monitored by staff located in an underground office who performed critical calculations by hand. Thanks to OCC fiber optic cable, mine operators now can monitor and fix problems from the surface—and even from remote locations, using a laptop.

“Communication and monitoring via fiber optic cable has revolutionized mining safety and operation,” said Dehn. “We have a far better picture of what is happening a mile below the surface and can monitor and correct situations in real time that may otherwise have resulted in accidents in the past.”

Dehn said that a new 4-strand cable was hung at the Galena mine in 2001 for additional monitoring, and an additional 6-strand cable installation is in progress to accommodate upgrades and to allow for future expansion. In 2010, the mine also installed 2,000 ft (610 m) of additional 4-strand cable to expand the system.

“We chose to stay with OCC cable because it survives,” she said. “Our choice has always been MSHA deployable cable because it has never failed, even though we operate in the harshest of environments.”

According to OCC, its B-Series MSHArated deployable mining fiber optic cables are designed to provide reliable communications and monitoring in hazardous and harsh mine environments. Major features include:

• OCC’s polyurethane Core-Locked jacket, extruded under high pressure directly over the cable’s core, resulting in a cable that has no voids and acts as one unit when bent or twisted.

•Helically stranded cable core for flexibility, deployment, survivability and mechanical protection for the optical fibers.

•Color coded sub-cables for direct termination.

•Crush-resistance and resiliency, with two separate layers of aramid strength members in the sub-cables for individual single-fiber connector or termination pin, and an overall layer for strain relief on multichannel connectors.