By Ken Ward Jr. Coal operators around the country will be required to install life-saving "proximity detection" systems on continuous mining machines in underground mines, under a rule being finalized this week by the U.S. Mine Safety and Health Administration.MSHA chief Joe Main said the rule, years in the making, will save coal miners from being pinned, crushed or struck by continuous mining machines, a type of incident that has claimed the lives of 35 coal miners nationwide since 1984."This is something whose time has arrived, both in terms of the technology and the need," Main said in an interview Tuesday afternoon.MSHA's final rule, to be published in the Federal Register on Thursday, includes a phase-in period of up to 36 months "to give mine operators ample time" to comply, the agency said in a prepared statement.Proximity detection systems can sense when workers get too close to mining equipment and shut down that equipment to avoid crushing and pinning injuries and deaths.