Nearly three weeks after a collapse inside the main access tunnel of a mine in Chile trapped 33 miners inside, all are reportedly alive, and recently began receiving emergency supplies through a bore hole. But rescue workers estimate it could be four months before this amazing story of survival plays out, when a two-foot hole will be drilled in the rock to retrieve the miners.
Here's what's known about the event at the San Jose gold and copper mine, and what's ahead:
What caused the collapse?
It's not yet clear. Earlier this week, Chilean President Sebastian Pinera said the cause of the roof collapse, about 1,100 feet (350 meters) below the surface, is being investigated. The mine is owned by the Compania Minera San Esteban Primera, which along with the National Mining and Geology Service, has come under criticism since the accident. In 2007, an explosion in the San Jose mine is reported to have killed several workers. Prinera has said the mine should not have been reopened without an escape route, according to media reports.
While there are many inherent risks involved in mining, it is the control of those risks that determines safety, Terence Foreback, a New Mexico state mine inspector, told LiveScience. Mining in the United States, in spite of its risks, is not among the top 10 occupations with the most injuries and fatalities, thanks to controls. However, in the Chilean mine, this risk does not appear to have been well managed, Foreback said. [The Worst Petroleum Disasters Ever]
Problems with the roof of a mine can most likely be attributed to one of two things, according to Foreback. Nearly all tunnels must be supported somehow, and a lack of support can lead to a collapse. The size of the tunnel can also be a problem: The larger a tunnel is, the more susceptible it is to collapse, he said.
What has hampered rescue efforts so far?
Two days after the roof of the mine collapsed and miners became trapped, rescue efforts hit a snag. Workers had been descending through a ventilation shaft toward a shelter, about 2,200 feet (670 meters) below the surface where the survivors were believed to be, when another cave-in blocked the shaft. The next day, Aug. 8, rescue workers began drilling bore holes, about 6 inches in diameter (15 centimeters), to locate survivors, according to Reuters.
On Aug. 22, more than two weeks after the initial collapse, the first bore hole reached the survivors, all 33 of them, who passed up a note, translated as: "The 33 of us in the shelter are well," according to Reuters. They received emergency rations and lights to stave off the darkness in the 540 square foot (50 square meter) room where they are living.
Rescuers plan to drill a hole, then widen it, so the miners can be pulled, one by one, to the surface, and they have estimated this could take three to four months, according to the BBC.
Why will it take so long to get the miners out?
To reach the miners, rescue workers will need to drill through a lot of rock. "It must be areas of fairly hard rock where the drill's going to have to drill through some pretty tough stuff," said Jeffery Kravitz, a U.S. Mine Health and Safety Administration technical expert.
Nevertheless, the drill will need to carve out a 26-inch- (66-centimeter)- diameter hole to pull the miners out. This task will be much more time-consuming than creating the bore holes, which were drilled to communicate with the miners and provide them with food and water.
Estimates for getting the miners out range from 30 days to four months, Kravitz told LiveScience. Though news reports have suggested the drill could cut through nearly 50 feet (15 meters) a day, "typically things go wrong," Kravitz said, such as drill bits breaking.
In 2002, nine miners were trapped for more than 78 hours in a Pennsylvania mine after water flooded in from an adjacent, abandoned mine. In a rescue effort similar to that begun in Chile, rescue workers first drilled a six-inch (15-centimeter) hole down 231 feet (70 meters) to the miners' location. Rescue workers then drilled two 30-inch holes nearby to retrieve the miners. Only one of the holes was completed after the drill in the second hole broke. The completed hole took more than 48 hours to drill, according to a report by the state's Bureau of Deep Mine Safety.
How did 33 men survive 17 days trapped in the mine?
"It's really not a miracle," said Laurence Gonzales, author of "Deep Survival: Who Lives, Who Dies and Why" (W. W. Norton & Company, 2003). "The reason those guys stayed alive so long is they were extremely disciplined."
Once communication was established with the ground earlier this week, the miners reportedly explained they had rationed their supplies, limiting themselves to two spoons of tuna, sips of milk, a bite of crackers and a morsel of peaches, stretching supplies intended to last two days over more than two weeks with leftovers.
"That is a starvation diet," Gonzales said in a telephone interview. "What these guys were doing, they were just keeping their level of nutrition just above starvation, I am sure they all lost a lot of weight."
Humans can last for weeks without food, but "food stress as they call it is tremendously debilitating," he said. "Your whole body cries out for the things you need, amino acids, fat, carbohydrates ... you can't think, you can't work."
Organization and purposeful action are key to surviving in a prolonged, life-threatening situation such as this, as is social connection, he said. "If you have something to get back to, you are more likely to get back to it," Gonzales said. People also do better if they can help others, he added.
How will they survive as much as 28 days more?
Now that the miners have access to food and hydration from the surface, one of the biggest challenges will be psychological.
"Stress is toxic, mammals evolved to use stress as an emergency feature of their physiology," Gonzales said. "These guys are in a very stressful environment, and it could eat away at them, and some of them, depending on their constitution may not hold up."
People who do not hold out psychologically can give up and die suddenly, he said.
The Chilean government has reached out to NASA for advice on how to keep the miners mentally and physically fit during what could be months of confinement.
Families above ground have sent and received personal messages from the trapped miners, but, as of Tuesday, the miners had not been told how long the rescue effort could last, the BBC reported.
How is a gold and copper mine different from a coal mine?
Coal mines are typically a lot shallower than gold and copper mines. In the United States, gold and copper mines can go as deep as 8,000 to 9,000 feet (2,400 to 2,700 meters), while the deepest coal mines are only around 2,000 to 2,200 feet (609 to 670 meters) deep, Kravitz said.
Coal mines also usually run horizontal to the earth's surface, while gold and copper mines can run any which way.
Coal mines also produce methane gas, which is highly flammable and presents a risk of explosion. Copper and gold mines don't leak methane gas and thus don’t present this risk. Copper and gold mines also can have large pockets of oxygen, which allowed the trapper miners in Chile to survive.
Copper and gold mines also are typically "wet mines" which drip water from the walls that can serve as a drinking supply.