The Atacama region in South America is a very large mining area producing great volumes of copper and gold, which together are the largest gross domestic product (GDP) providers in Chile. Labour comes not only from Chile but also the neighbouring countries. The miners are drawn to the higher paying locations, which are also the most dangerous. These range from semi-illegal operations employing just a handful of people to the larger mines with 600-700 people.
Yet there are only three government mine inspectors in the country. With more than 800 mines registered at the time of the incident, this obviously becomes an all but impossible task for any body of inspectors. Codelco is one of the largest employers that run very safe operations underground but unfortunately this culture does not occur in all other mine operations. The fact that Codelco had operations in the Atecama range meant very good help was soon at hand, but even then with vastly different mining techniques and geology, it was never easy.
San Jose
The scene of the 2010 accident was the San Jose mine in Northern Chile. It started life in 1889 with the existing headgear over the access shaft having been in place since around 1910. The ropes for this do not go down the full depth of the mine, so were no good for the rescue from the deep levels. The access shaft was further laid to waste by the removal and sale of many of its ladders in a bid for extra revenue, no doubt by would-be employee entrepreneurs rather than a planned removal by management themselves.
Mining at San Jose has mostly been continuous since it opened except for a short closure in 2009 due to a dispute between the miners and owners over the safety of the mine. It still made a profit of USD 20M that year. There had been eight deaths in 12 years with the last in 2007 but this made little impact on the safety of the mine. This just emphasises the culture of both the mine itself, and the general area culture.
The mine is about 600km north of Santiago and 90km from the coast. Being a mountainous region, the transport of equipment to the mine takes about five days from the sea.
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By GlobalDataCollapse
On the afternoon of 5 August 2010, a section of the mine from 350m deep to 630m deep completely caved in, although, of course at the outset, this was unknown. This was day 0 for 33 miners in the deepest levels of the mine. This collapse surpassed any mine collapse before it and shocked the international mining community.
The 8.5km long ramp used to access the mine face had completely failed. It is believed that overmining of the ramp structure itself led to the collapse.
In an effort to make the mine more productive, the operator had remined the ramps support structure for any gold or copper left in it.
Immediately following the collapse all communication was lost with the trapped miners and it was impossible to know if anyone had survived.
Rescue workers and the Chilean Government officials were quickly on the scene but with no accurate plans of the mine at all it was difficult to start assessing the damage. The plans now available were drawn after the event. The extent of the collapse was also unknown initially though it was thought that engineers could re-mine the ramp through the collapsed section to reach the miners.
This started but stopped soon after it was realised it was futile and possibly fatal to continue, with the collapsed ramp and access shafts providing further dangers to rescue teams.
Other attempts to access the lower levels via the shaft system also failed due to blocked accesses and ongoing collapses, fortunately with no disastrous consequences during these brave efforts.
With remining ruled out, Codelco sent 18 rigs to bore pilot holes to attempt to locate the trapped miners. Without accurate plans of the mine it was down to the mine’s foreman to guide the boreholes. Standing at the mine entrance the foreman paced out his journey down the ramp in his mind and suggested rig positions. Drilling operations were fraught with difficulties as drill bits encountered hard ground and existing mine plant and equipment.
As drilling continued it became clear that the mine was completely choked from 350m to 505m depth – proven by lowering a video camera – and at this point many were considering giving up. From a consensus on conversations between the mine rescue teams, until the full mine depth had been reached, there was still a possibility of finding live people. The Chilean government also supported this decision.
Contact
Two days later, on day 14, the drill had reached 670m depth and found a void. The drill was pulled back so a CCTV camera could be lowered down. Upon pulling the drill out, the rescuers were shocked to see a poly-pocket on the end of the drill bit with the now famous note inside explaining that all 33 miners were alive at a refuge chamber.
It was decided to continue drilling with three rigs as a contingency in case any of the drill holes collapsed. The first hole was used as a supply route for water, food, messages and medical equipment.
On day 17, a camera was put down that allowed the first view of the miners. Obviously no medical staff could reach the miners for medical assessment and treatment but proper food and supplies, such as antibiotics, could be delivered. Experts from NASA advised that no solid food was to be delivered initially. Only high energy drinks and liquids to rehydrate the miners, much to their consternation, though NASA also supplied a rolled up TV screen with DVDs for the miners to watch. The supply hole allowed charged light to be sent down which would last for 24 hours and was continually resupplied. Later on, ventilation was supplied with cool air along with cables for video conferencing.
The miners’ only lighting had been their cap lamps, which ran out early on. A Toyota SUV was then used with its engine running to keep the headlights running. Once that had run out, water from the radiator was used for drinking water. Cannibalism had also been discussed.
Three drill rigs attempted to bore holes large enough for the rescue. Plan A was a Strata 950 raise borer. This was the slowest method as a pilot hole needed to be driven first and then a reamer fitted and the hole enlarged bottom-up. Plan B was a T130XD air core drill that was used to widen one of the three 140mm boreholes already supplying the miners. Plan C was a RIG-421 oil drilling rig that could make a single pass. It was risky as it was difficult to aim the rig at such a small target. As plan B progressed cuttings fell down the shaft and needed to be shifted. The 33 miners were engaged in removing excavated material. The foreman arranged three shifts over 24-hours and it proved to be a huge morale booster. Though second to start, after the raise borer, plan B was successful.
Extraction
On day 66, it was possible to lower down and test Phoenix Two, the rescue capsule. The hole also passed through two roadways so it had to be a set length so it did not deviate off the required angle. Communications were maintained throughout the extraction process.
Two paramedics were sent down to check the miners over before they were allowed out. On day 67 the miners were all successfully rescued with no major injuries. Some of the miners did suffer from medical problems after the rescue including dental problems due to the acidic water form the car radiator, with some requiring surgery. Silicosis problems were present.
The cost of the rescue operation has not been finalised but estimated at between USD 10M and USD 20M. There were up to 800 people on the surface helping with the rescue attempt.
The assets of the mine were seized by the government five days after the mine rescue operation to help pay for the costs with the rest provided by Codelco and the Chilean government.
Future Planning
In planning for future events, the supplies the miners had to rely on were looked at. Before the miners were reached, they only had the food with them and emergency food for two days.
The foreman had begun a rationing process with two spoonfuls of tuna, one biscuit and a little milk every 48 hours until the supplies were exhausted on day 16. The miners experienced an average weight loss of 8kg each.
Lessons could be considered for any major mining or tunnelling project. With a full face TBM and lining behind, the chance of a similar incident occurring is very low. However a flooding event in South Wales in September 2011 that led to the deaths of four miners was also thought to be a thing of the past yet showed how susceptible to disaster, either natural or man influenced, such operations can be.
In tunneling, if boreholes were sunk for rescue attempts in a major city for instance, the existing infrastructure may well preclude large areas from being used for drilling attempts leading to angled/inclined borehole. Because of generally shallower depths for tunnels, hole speed should be increased. Steel reinforced concrete tunnel linings could cause problems for drill heads.
For mining operations in the UK a register of personnel and equipment that could possibly be used in excess of 1,000m depth has been assembled. If a similar rescue attempt would be required for a tunnel operation, such planning would save huge delays occurring. We now have transportable refuge chambers for fire or gas incidents, it’s time to go that little bit further
