Mining has resumed at a Montana coal mine where high levels of dangerous carbon monoxide gas prompted a shutdown of most underground operations that lasted three weeks.
Signal Peak Energy spokesman Mike Dawson said Friday that nitrogen pumped into a portion of the Bull Mountain mine had lowered concentrations of the gas to safe levels. He says mining resumed late Thursday.
Federal safety inspectors cleared the company to resume some underground maintenance work earlier this week. Prior to that, work was restricted to the mine's surface while the gas problem was addressed.
The high carbon monoxide levels were found Dec. 1 in an area away from active mining.
The 300-employee mine is north of Billings near the community of Roundup.