Danger Around Every Corner Deadly Rock Bursts Are One Of The Biggest Hazards North Idaho Mine Workers Encounter

Rudy Carlson heard a rock strike his hard hat, then he was buried under six feet of debris.

A rock wall in the Coeur Mine had blown out behind him.

Carlson was shoved against a nearby post, which probably saved his life. It created an air pocket for him to breath during the 21 minutes it took co-workers to dig him from the rubble with their hands.

The 49-year-old miner suffered seven broken ribs and a compressed vertebrae in the May 29, 1998, accident. He spent 17 days at Sacred Heart Medical Center in Spokane.

But the Osburn, Idaho, resident, a miner for 25 years, just counts himself lucky to have survived one of the Silver Valley’s rock bursts.

“It was a miracle,” he said. “I’m thankful to the good man above.”

Rock bursts are sudden, explosive failures in underground mines that can turn tons of rock to rubble within seconds. For more than a century, they’ve confounded mine managers and researchers.

Two days before Christmas, 100 miners were sent home from the Galena Mine after two workers were injured in separate rock bursts. Part of the mine remained closed for five days while the federal Mine Safety and Health Administration investigated.

“It is not certain why the series of bursts occurred,” concluded a 14-page report from the investigators.

Despite 50 years of intensive study and research, many aspects of rock bursts remain a mystery.

Engineers know what types of rock formations are prone to bursting. But only in a handful of cases worldwide have they been successful in predicting rock bursts in time to get miners out of harm’s way.

“It’s like trying to predict an earthquake,” said Elaine Cullen, communications manager for the Spokane Research Lab, whose researchers are considered world experts on the phenomena. “We know what zones they are likely to occur in, but we can’t predict when they’ll happen.”

Like earthquakes, rock bursts are seismic events. Pressure builds in the rocks surrounding an open area underground, until the rock fails.

“Imagine putting your hand on a water glass and squeezing and squeezing and squeezing until it eventually breaks,” said Ed Wilson, a safety director at Hecla Mining Co.

Rock bursts were first observed in the Silver Valley in the 1930s. The first fatalities occurred in 1941, when two miners were killed during a major rock burst at the Sunshine Mine. Rescue crews moved the equivalent of 600 train car loads of rock to recover the bodies.

It’s impossible to estimate the millions of dollars in damage and lost production over the years, or the emotional toll on workers, Wilson said.

“Rock bursts in a deep mine drives everything you do,” he said. “It influences how much you mine, where you mine, what methods you use, the ground supports, and how often you can blast.”

The possibility of getting trapped by a rock burst is always in the back of miners’ minds.

“There have been stopes (work areas) I dreaded to go into, day after day. I knew it was just a matter of time,” said Web Cotter, who mined in the Silver Valley for 18 years and badly injured his left hand in a 1976 rock burst.

Still, most miners aren’t fatalistic, Cotter said. Three years after the incident, he returned to mining until an unrelated accident forced him to quit.

Carlson went back to a job above ground at the Galena Mine in January. He hasn’t ruled out a return to mining.

Rock bursts are characteristic of areas where miners work deep underground, excavating ore from brittle rocks, said Wilson Blake, a Hayden Lake resident who consults internationally on rock bursts. In addition to the Silver Valley, they’re prevalent in just three other hard-rock mining areas - Ontario, Canada; South Africa; and the Kolar gold fields of India.

Tunneling into the earth is like submerging a submarine, according to one engineer. The deeper you go, the more the pressure increases.

In Silver Valley mines, the pressure on underground openings is both vertical and horizontal, Blake said. Every time a new opening is created, “you’re changing the geometry of the area” - shifting the pressure along the rocks, he said.

And since the Silver Valley contains quartzites - billion-year-old rock as brittle as it is old - it can shatter when it fails.

“Most of (rock bursts) are harmless,” said mining engineer Jeffrey Whyatt. “Hiding in all those events are a few that are dangerous.”

Those are the ones researchers want to predict and prevent, he said.

Whyatt works for the Spokane Research Laboratory, part of the National Institute for Occupational Safety and Health. He’s been involved in rock burst research for 10 years.

A computer screen in his office shows areas of the Lucky Friday Mine in Mullan. Dots mark where rock bursts have occurred; colors code their magnitude.

Whyatt and his co-workers hope the meticulous tracking will yield more clues about the correlation between geology and rock bursts. Mining companies in the Silver Valley work closely with the Spokane Research Laboratory, sharing information about events. They also have their own tracking systems.

“The difference is that we’re on the research end,” Whyatt said. “They’re working in real time.”

At the Galena Mine’s offices in Silverton, Idaho, engineering technician Matt Kurkowski also sits in front of a computer screen. The computer is tied into sensitive acoustic equipment that “listens” to the noise made by rocks deep in the mines.

The equipment tracks rock failures in the mine. It also records “rock talk” - the sound waves emitted by rocks adjusting to the stress created by mining.

The information influences daily and long-term decisions at the mine. Each shift gets a map of where rock failures have occurred in the previous 24 hours, to alert them of potential problems areas.

Engineers carefully track areas of the mine where sounds have changed and the rock may be building up stress.

“It’s a tool. Obviously, bursts can still happen,” said Mike Lee, general manager of Silver Valley Resources.

Blake, the mining consultant, was instrumental in refining the acoustic equipment in the late 1960s and early 1970s when he worked for the Bureau of Mines. Before computers were common, he and co-workers would go into mines during blasting - when rock bursts are most likely to occur - to record rock noise with hand-held equipment.

“It’s not bad at telling you where the problems areas are,” Blake said. “But it’s never been successful as a predictive tool.”

In the past 25 to 30 years, a number of technologies have been developed to help contain rock bursts, Blake said.

Four-foot-long steel bolts hold tons of rock in place. Some areas considered high risk for rock bursts are “de-stressed” to trigger the bursts when workers are out of the mine. Mining methods and the rate of mining are adjusted to reduce the risk.

Though mining has become safer, there’s still no way to control the large events, Blake said.

“Whenever there’s a rash of fatalities, there’s lots of publicity,” he said. That leads to more quests for answers.

“Unfortunately, there’s really not that much you can do,” Blake said.

These 3 sidebars appeared with the story:

1. MINE SAFETY Unpredictable rock Engineers once thought that mines deeper than 4,000 feet could not be excavated without massive rock failure and rock bursting. However, one of the deepest U.S. mines — the Homestake Mine in South Dakota — has been mined at depths of 8,000 feet without experiencing rock bursts.

2. A LOOK BACK A fatal burst In a 1994 newspaper account, miner Don Campparelli described a rock burst in the Sunshine mine that killed his partner, Jim Finlay. “One second we were standing there, the next second we were totally buried and in pain. Totally packed in rock,” he said. Every time the two men exhaled, the rubble sifted tighter around their chests. “I knew my partner was there, I could feel him struggling to breathe. Then he quit,” said Campparelli, who was rescued a short time later.

3. WAR EFFORT PROMPTED OPENING OF RESEARCH LAB The Spokane Research Laboratory got its start because of rock bursts in Idaho’s Silver Valley. It opened in 1951, during the Cold War. The lead, zinc, copper and silver produced by the Silver Valley mines were considered “strategic and critical minerals” for the war effort, said Dale Avery, a data specialist for the lab. The government wanted to ensure a safe, continuous supply. The lab has had it’s share of successes. Researchers there worked closely with Hecla Mining Co. to develop mining methods that reduced rock bursts at the Lucky Friday mine in Mullan, Idaho. The mine shut down in 1986 and stayed closed for more than a year after a number of rock-burst injuries and fatalities at the mine. Low silver prices played a primary role in the closure, said Ed Wilson, a safety director at Hecla. But the company also used that time to revamp mining methods to reduce the risk of rock bursts, he said. The Spokane Research Laboratory was part of the U.S. Bureau of Mines until that agency was dissolved in 1996 during government downsizing. It’s now part of the National Institute for Occupational Safety and Health. About 80 researchers work on a variety of safety and health issues related to mining. By Becky Kramer