Samples taken from inside the Upper Big Branch South Mine show that levels of dangerous gases are still too high to allow rescuers inside, a mining official said Wednesday.

A drill pierced the chamber where four unaccounted-for miners are believed to be at 4 a.m., said Kevin Stricklin, an administrator for the Mine Safety and Health Administration.

The first sample showed about 14,000 parts per million of carbon monoxide, 10,000 parts per million of hydrogen - both considered high - and 3 percent methane, he said.

Though the latter reading by itself would not necessarily be dangerous, the combination "puts it in an area close" to being explosive, he said.

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