Three miners remained in North Idaho hospitals this morning after a rock burst at the Lucky Friday Mine in Mullan, Idaho, injured seven miners Wednesday night. The rock burst was strong enough to register on seismographs. It was the third accident at the mine this year. Two miners died - one in April and one last month - in the other incidents. Seven miners Wednesday night were transported by air and ambulance to area hospitals, according to the Shoshone County Sheriff’s Office. Six were taken to Shoshone Medical Center, where two were held overnight for observation, a nursing supervisor said. Injuries were mostly cuts and bruises. A seventh miner was taken to Kootenai Medical Center and was listed in fair condition there this morning. Their identities were not released. All crew members got out of the mine. Seismographs throughout the region recorded the energy of the rock burst as a 2.2-magnitude quake, but scientists said the shaking came from the burst itself. The readings gave the location as Mullan. “That was the signature of the rock burst, I believe,” said Mike Stickney, director of the Earthquake Studies Office at the Montana Bureau of Mines and Geology. A team from the U.S. Department of Labor’s Mine Safety and Health Administration was sent to the mine overnight to investigate the accident. The agency ordered the mine closed and will keep it closed until it determines work conditions again are safe, spokeswoman Amy Louviere said this morning. Phil Baker, president and CEO of Hecla Mining Co., the operator of the mine, said in a statement, “We are thankful that all employees are out of the mine and have been accounted for, and that those injured have been treated. The safety of our employees is our primary concern.” Baker said the company will investigate the cause of what the company described as seismic activity that led to the burst. The miners were installing a liner system in a “haulage way,” an area used for moving ore with vehicles. The liner - a mix of mesh and a concrete fill material - was being installed to control rock bursts and was part of an effort to ensure mine safety, said Melanie Hennessey, vice president of investor relations for Hecla. Reports from Wednesday night indicated that an emergency call was made to Shoshone County authorities at 7:51 p.m. to report buried miners. Law enforcement, medical emergency personnel and an underground mine rescue team were dispatched to the deep underground silver, lead and zinc mine. The miners were trapped 5,900 feet underground after a rock burst, said Hennessey. She said no rock blasting had taken place for the past 24 hours, so the incident was deemed due to seismic activity, not mining operations. The latest incident comes just weeks after the death of miner Brandon Lloyd Gray, 26, who was killed after being buried in rubble while trying to dislodge a jammed rock bin. He died two days after the Nov. 17 incident. Mine safety officials and Gray’s employer, Cementation U.S.A., the company hired by Hecla to deepen the mine, are investigating that incident. In April, Lucky Friday miner Larry “Pete” Marek was crushed after his work area collapsed. Federal regulators with the MSHA found company safety failures that led to Marek’s death with four citations and $1 million in penalties in the April collapse. Investigators in the accident report said that “Management did not conduct an evaluation, engineering analysis, or risk assessment to determine the structural integrity of the stope back (the roof of an open room beneath the surface).” The report continued its focus on management failures. “Management policies, procedures, and controls failed to ensure appropriate supervisors or other designated persons examined and tested ground conditions to determine if additional ground control measures needed to be taken to ensure the safety of miners prior to commencing work in the stope.” The mine is undergoing a $200 million project that will deepen the mine nearly 9,000 feet, providing access to deeper ore. Hecla officials expect the project to be completed by 2014. Hennessey said the company recently hired a geotechnical expert to work with the mine and with the mine’s geotechnical consultants. Hecla was established in 1891 in North Idaho’s Silver Valley, according to the company’s website. The fatalities earlier this year came after a 25-year period with no deaths, Hennessey said.