As the day that will bring the trapped miners in Chile above ground approaches, geologists and engineers are evaluating the risks of the rescue mission, for both the miners and the rescuers.

"They've taken a lot of precautions and thought of everything that could possibly go wrong," said John Urosek, chief of mine emergency operations for the United States Mine Safety and Health Administration. "Their biggest concern is if something happens that is out of their control."

The riskiest part of the rescue operation, Urosek said, will be transporting the miners, one by one, to the surface in a cable-supported capsule called the Phoenix.

Preparations

After digging a 680-yard (622-meter) tunnel, and drilling through to the miners on Oct. 9, rescue teams are conducting test runs and evaluating the stability of the capsule that will carry the miners to freedom. The 33 miners have been trapped underground since Aug. 5, when the gold and copper mine caved in, near the city of Copiapó in Chile.

After geologists and engineers surveyed the route's conditions by snaking a video camera down the tunnel, they concluded that some areas of the upper walls were at risk of cracking, and needed to be reinforced with steel pipes, Urosek said.

The steel casing that lines portions of the wall is meant to prevent rocks from breaking loose and wedging the capsule in place as rescuers attempt to navigate it through the tunnel. These chipped-off stones pose the biggest threat to hindering the rescue mission, as the capsule will have only about two inches of clearance, Urosek told Life's Little Mysteries.

Risks the rescuers face

Rescuers above-ground face safety threats as well.

"If, heaven forbid, the hoisting rope carrying the capsule were to break, the capsule would free-fall, harming the miner inside and those still below," Urosek said. "Because the cable is over 2,000 feet long, it is under a lot of pressure, and if it snaps, it could shoot back up through the opening and whip around, possibly injuring those near it."

While Manuel Montesino, the superintendent for production at the state mining company Codelco, told news sources that the ride to the surface may take as little as 11 to 12 minutes, Urosek estimates that each miner's one-way trip could take as long as 40 or 50 minutes to complete.

This is because the shaft, which is 2.33 feet (0.7 meters) in diameter, does not follow a straight, vertical path. It contains bends and turns that will require the Phoenix to twist several times throughout its claustrophobic journey.

Because of this, rescue teams will have to carefully gauge the pod's speed, Urosek said.

This article was provided by Life's Little Mysteries, a sister site to LiveScience.