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The recent accident in Chile that trapped 33 miners underground for almost three weeks and counting has drawn attention to the dangers of wildcat mining, or the operation of illegal mines.

Such illegal mines and mining practices occur across the globe, including the United States, but they are particularly popular in China, India, Indonesia and the Democratic Republic of the Congo (a state in Central Africa), according to the U.S. Geological Survey's Mineral Resources Program. In the United States, officials are cracking down on unlawful and unsafe mining activities.

Explosions and roof collapses are possibilities when regulated companies with vast experience and resources are mining, said Phil Smith, director of communications for the United Mine Workers of America, an industry union. "The chances of somebody eventually getting seriously injured or killed  are close to 100 percent," when mining is conducted outside of regulations and with few or no resources to maintain safety, he said.

What makes wildcat mine operations so dangerous is that they have no state or federal inspectors to check that the mine is safe, and the training of workers is often unstructured and done only on the job, resulting in injuries and disasters, according to Mark Radomsky, director of the miner training program at Penn State University.

Accidents and fatalities happen when wildcat workers are forced to operate dangerous and complicated machinery without undergoing proper training. Questionable and inadequate mining methods are also common, Radomsky told Life's Little Mysteries.

Wildcat mining can also refer to mines that have the required authorization to dig but they also support illicit mining activity, according to the U.S. Department of Labor's Mine Safety and Health Administration (MSHA). Mines like these may dig deeper than allowed or not follow required safety protocols. For example, they may fail to provide adequate ventilation to reduce the risk of explosions and lower miners' exposure to coal dust (which causes black lung, according to the Occupational Safety and Health Administration).

On Tuesday, MSHA announced that they had uncovered dozens of safety violations at four underground U.S. coal mines  during recent surprise inspections. Located in Kentucky, Tennessee and West Virginia, the violations included failure to follow ventilation plans, inadequate roofing and dangerous build-up of explosive materials.

(The Chilean mine accident occurred in a copper and gold mine.)

"It is appalling that our inspectors continue to find such egregious violations, especially with the explosion at Upper Big Branch still fresh in everyone's minds," Joseph Main, Assistant Secretary of Labor for the Mine Safety and Health Administration, said in a statement.

MSHA increased the investigation of wildcat mines following the April 5 explosion  at Massey Energy's Upper Big Branch mine in West Virginia, which killed 29 miners and is the worst mining accident in the United States since 1970, according to the Centers for Disease Control. Investigations have suggested safety violations at that mine.