Fatal error left miners at mercy of landslidePublished by MAC on 2003-11-01
Fatal error left miners at mercy of landslide
Syndey Morning Herald
November 1 2003
Matthew Moore, Herald Correspondent and Karuni Rompies in Jakarta
The operators of the world's richest goldmine had more than two days' warning that a landslide was imminent before it arrived in a torrent of 2.5 million tonnes of rock and mud that killed eight workers.
The managers at the Freeport-McMoRan company had wrongly calculated that the slide would be slow enough and small enough to stop on a 90-metre wide step cut into the wall above the workers they left at the bottom of the pit.
Although heavy rain had fallen for five days, the managers did not realise how much water was trapped in the slope and that the debris would pour over the step onto the workers, according to information provided to the Herald by investigators.
Three weeks later, four bodies remain buried at the bottom of the pit, more than 4000 metres up in the mountains of Papua, just a few kilometres from the only glaciers in South-East Asia. Four bodies have been pulled out and five people are recovering from injuries, including Muhammad Samsuri, who is in a Townsville hospital bed after losing both legs.
Among many of the workers at the Grasberg mine, 16 per cent owned by the [British] Australian mining company Rio Tinto, there is deep concern about whether more should have been done to avoid the disaster.
A week after the October 9 tragedy, the company's chairman and chief executive, Jim Bob Moffett, sought to play down the size of the slide and its impact on production when he addressed financial analysts.
". . . We move 750 [thousand] up to a million tonnes a day and just to be straightforward with you if we had to focus all of our earth-moving equipment on this we could clean it up in three days. "
Although he promised Freeport would do what it could to find out what happened, he did not mention the data it already had that showed a slide was imminent.
Because the south wall where the slide took place was always most at risk, the company had rigged it with more than a dozen extensometers - devices that measure the rate of movement.
Every 20 minutes, any shift was recorded on a computer graph, and the results discussed at meetings twice daily.
Dr Anthony Meyers, Australian liaison with the International Society of Rock Mechanics, said small movements were not something to worry about. The danger came if the rate of movement began to accelerate.
In August and September the rate of movement began to increase from about 4 millimetres a day up to 8mm, and then 10mm before moving back down, says an investigator, Witoro Soelarno, of the Indonesian Department of Energy and Mineral Resources.
The Grasberg mine's operating procedures say that movement of more than 10mm a day means "possible pit slope failure". In early October, the slope continued to pick up speed and by October 5 parts of it were moving at 20mm and 30mm a day, Mr Witoro said.
On October 7, two days before the slide, Freeport moved its stationary mining equipment on the 90-metre step out of the zone where it expected the slide to hit.
But below the step, it was work as normal for the drivers of the 240-tonne trucks and the bulldozers, and mechanics like Muhammad Samsuri. Just before dawn on October 9, he and two friends were working on a pump in the open when he looked up. "I saw the mountain split into two," he said. "Then I ran, I was confused, I was nervous, where should I run to?"
Mr Samsuri and one friend headed for the shelter of a small water tank, while the other friend ran the opposite way. There was no way out for any of them.
Mr Samsuri was knocked unconscious by the rubble which buried him chest-deep, although he woke up when given drugs. "The one next to me was already unconscious. I could only see his head. I think he was already dead. The other one, Budi Kuncoro, I could only hear him screaming for help. According to my wife, I am the only one who is alive from the three of us."
Peter Lilly, chairman of mining engineering at Curtin University, said such large loss of life was very rare in open-cut mines because slides can usually be predicted. Engineers monitored the weak spots and, if they started to move, managers moved workers out of the way.
Freeport did not move its workers out of the path of the slope failure because it did not expect the slide to be so liquid.
The seven piezometers it had in the slope to warn of a build-up of water were not in the right place to alert them of a "pocket" of water high up.
Mr Witoro said Freeport had already mapped the water pockets in the area but was not worried about them filling up because they normally drained themselves.
Given that history, the company could not have predicted what happened without monitoring those pockets.
"So far there has been no experience like this . . . Usually there are many cracks in this. Water comes out. But not this time. Now, the water comes in and stays there."
Mr Witoro does not blame Freeport for putting workers at the pit bottom when it knew a slide was coming because "the systems seemed to work well". But now major changes, including the use of drainage systems, might be needed to keep water out before mining could resume.
Freeport declined to respond to all questions from the Herald about the evidence that a landslide was imminent, or what considerations they gave it. "We have always been strongly committed to safety in all phases of our operations and our safety department has a very good record," it said.