MSHA issued new final rules Tuesday requiring coal operators to equip their continuous mining machines with proximity detection technology, which can make visual and audio warnings or turn off a machine when it is too close to a person or an object. Miners will wear a component that also provides a warning.

The rule, which takes effect March 15, will allow the industry to phase in retrofitting warning systems on existing machines over a period of up to three years. New machines must have the devices by November 2016.

Of an estimated 863 continuous mining machines operating in underground mines, about 425 already have been equipped with proximity warning systems, according to MSHA.

There were 326 active underground coal mines operating in the United States in 2013, employing 42,314 workers, the agency said. It will cost the industry about $47 million to comply with the new rule over the next 10 years, MSHA estimated.

Kentucky mines employ about a quarter of the nation's miners and ranks third in annual coal production, behind Wyoming and West Virginia, according to the National Mining Association.

The industry group is still reviewing the regulations, "but on first blush we're pleased it appears to reflect our limited experience with the technology and our comments to the agency regarding that experience," said spokesman Luke Popovich.

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