The two workers killed in an underground coal mine in West Virginia were performing a risky method known as retreat mining, where the roof is intentionally collapsed to retrieve more coal.
Retreat mining has been going on for generations and is considered standard practice in mines where coal reserves are running out. It involves yanking supporting pillars of coal from inside the mine and letting the roof collapse as miners and equipment work their way out.
The son of one of the workers who died Monday night at Brody Mine No. 1 said his father understood the risks.
"That's one of those things you always think about when you work in the mines," said Caleb Hensley, whose father, 46-year-old Gary Henlsey, was killed.
Hensley's co-worker, Eric D. Legg, 48, also died. Friends said they both liked to hunt and fish.
"It's a very dangerous profession," said Legg's friend Barry Brown, who has been a miner for 37 years. "You don't know when something like this is going to happen. It floored me."
Federal officials said the mine had so many safety problems it was deemed a "pattern violator," a rare designation reserved for the industry's worst offenders.
Brody No. 1 was one of only three mines last year to earn the label that regulators have put greater emphasis on since the 2010 Upper Big Branch explosion killed 29 miners about 10 miles away.
The designation subjects the mine to greater scrutiny from regulators, and it's the strongest tool the Mine Safety and Health Administration has, said Kevin Stricklin, the agency's administrator of coal mine safety and health.
"We just do not have the ability or authority to shut a mine just because it has so many violations," Stricklin said.
Brody No. 1 is owned by a subsidiary of St. Louis-based Patriot Coal, which in its annual report last December blamed the problems on a previous owner and said it was "vigorously contesting" the designation.
The company said the workers were killed during a severe coal burst, where high-speed coal is shot at anyone in the way. The burst occurred as they were doing retreat mining.
"Preliminarily, it looks like it was a rock outburst from the wall of the mine, which basically inundated the entries with coal and debris," Stricklin said. "That's what caused the two fatalities."
In August 2007, six miners doing retreat mining at Utah's Crandall Canyon died in a collapse and 10 days later, three rescue workers were killed in another cave-in.
In October, Brody No. 1 was added to a Pattern of Violations list for repeatedly breaking federal health and safety regulations over the previous year. It was cited for 253 serious violations.
Stricklin said that since October, the company was slapped with 69 violations that required at least partial closure of the mine each time.
Asked for comment on its safety record, a Patriot Coal spokeswoman referred to the company's latest annual report. Patriot's subsidiary purchased the mine Dec. 31, 2012.
In 2013, MSHA issued 514 citations, orders and safeguards, the agency said.
It wasn't immediately clear whether any of the violations could have had anything to do with a coal burst.
The Mine Safety and Health Administration has taken several steps to improve its enforcement of safety regulations after the Upper Big Branch explosion, the worst U.S. coal mining disaster in 40 years. Among them: impact inspections of problem mines, such as Brody No. 1, and "Rules to Live By."
Last week, MSHA reported that eight miners died in accidents in the first three months of 2014.
Brody No. 1 employs about 270 workers.
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