Two miners were killed and twenty were injured after a mining accident occurred in Ouray, Colo. early Sunday morning. The accident was ruled to be neither a cave-in nor a mine collapse, but the exact cause of the problem has not yet been determined, other than that it was a "powder-smoke incident" that released chemicals which injured the miners.

Coroners initially said that the victims died of carbon monoxide poisoning, which is a standard byproduct of using explosives in mining. However, the crew working on Sunday was not detonating explosives, and it is believed that lingering CO from the previous day is what caused the injuries.

A spokesperson for the mine was unable to say whether the workers were wearing safety devices that monitor toxic gas levels, but according to NPR, "the publication Mine Safety and Health News says the accident rate at the mine is 115 percent higher than the national average."

As of the end of September, 27 miners had died on the job this year. The average statistic over the past five years has been 46. All but two of the injured have been released from the hospital.

[Pictured: the mining town of Ouray, Colo.]