By James Nelson

HUNTINGTON, Utah, Aug 11 (Reuters) - Rescuers trying to reach six coal miners trapped in a collapsed Utah mine broke through into their presumed location with a second, wider drill on Saturday and prepared to lower a camera into the cavity.

Mine co-owner Robert Murray, chairman of Murray Energy, said it would take a couple of hours to pull the nearly 9 inch (20-cm) drill bit out of the hole so a video camera could be lowered into the mine.

The equipment will be able to show 100 feet (30 metres) in each direction and provide better details of the conditions underground.

The men have not been heard from since Monday when part of the Crandall Canyon Mine near Huntington, Utah, collapsed.

A first, 2-1/2 inch (6 cm) drill pierced into the chamber late on Thursday but there was no sign of life when a two-way microphone was lowered 1,800 feet (550 meters) into the mine.

Rescuers said survey equipment later showed the first drill had "drifted" some 85 feet (26 metres) as it made its way down from the surface and may not have pierced into the cavity where the men were thought to be stranded.

Tests taken with instruments fed through the first hole showed that the oxygen levels in the chamber were too low to sustain life, although no other toxic gases were detected.

It will take rescue crews four to five days to create an opening large enough to reach to pull the miners out but if they are alive, the hole can be used to provide food, water and air.

Officials say the men could potentially survive for weeks in an underground chamber if they were not killed by the initial collapse.

Murray has insisted that an earthquake triggered the mine's collapse but geologists dispute that, saying that shaking recorded by their instruments was caused by the cave-in.

Controversy has also risen over reports that the miners were engaged in a dangerous operation called "retreat mining" when the shaft collapsed -- though Murray has denied that such a technique was being used.

Retreat mining involves supporting the mine's roof with a column of coal, then removing those pillars and allowing the shaft to collapse as miners move to safety.

The Crandall Canyon Mine is on a high desert plateau some 140 miles (225 km) south of Salt Lake City, in what is known as Utah's "castle country" because of the towering rock spires that dot the bleak landscape. (Additional reporting by Dan Whitcomb in Los Angeles)

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