The crack runs for about 36 feet "outby" -- toward the mine's opening -- from the longwall section mining face, the geologist said. When it reaches a crosscut tunnel, the crack itself disappears, but the floor heaving continues for another 10 feet, the geologist said. The crack is about five inches deep and the floor heaving is six to 10 inches high, MSHA's geologist found.

Also, the geologist found that the crack is not "rooted," meaning it doesn't appear connected to the coal seam or a void below the active mining area, officials said.

"It wasn't a massive crack," Stricklin said. "It was what you would typically see in a longwall mine."

MSHA officials have not said the floor crack and similar smaller cracks are not evidence worth examining. Instead, they have disputed Massey's description of their size and the conclusions the company has drawn from the cracks' presence in the mine.

Such cracks and floor heaving is typically caused by the shifting of ground pressures during highly mechanized longwall mining, and can release methane from coal seams and geologic formations below.

Since early June, federal and state investigators have focused on, among other things, incidents in 2003 and 2004 when methane "outbursts" from the mine floor inundated the Upper Big Branch with the explosive gas. No ignitions or injuries were reported in those two incidents.

MSHA documents show Massey had proposed a number of steps, including de-gasification wells, to prevent a recurrence, and federal experts proposed additional measures, but MSHA has been unable to explain which of those steps were eventually implemented, and Massey has not responded to questions about the matter.

"There may be a crack in there that was involved in the explosion," Stricklin said, "but we don't know that yet."

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.

CHARLESTON, W.Va. -- A crack in the floor of Massey Energy's Upper Big Branch Mine measures 36 feet long and appears to be the normal result of the geologic stresses caused by longwall mining, U.S. Mine Safety and Health Administration investigators said Friday.

MSHA geologist Sandin Phillipson went underground Thursday to re-examine and measure the crack. Families of miners killed in an April 5 explosion said Massey officials had told them the crack was 100 to 150 feet long and possible evidence that the disaster could not have been prevented.

In an interview Friday, MSHA coal administrator Kevin Stricklin again disputed Massey's characterization and said even if methane escaped from a floor crack, proper safety precautions could have prevented the 29 deaths at Upper Big Branch.

"There's no reason for anyone to die because of a methane inundation," Stricklin said. "There are steps that can be taken and measures that can be put in place."

Earlier this week, the crack's size and its potential meaning in the investigation became the focus on the ongoing public relations battle Massey is waging with MSHA over the Upper Big Branch disaster.

After MSHA disputed the description of the crack that Massey gave to families, the company fired off one news release with previously released photos of the crack and another with the government's photo log to prove the pictures were authentic.

Massey also clarified that, at the time, the crack had not been measured, but that company officials estimated it to be about 50 feet long.

The skirmish prompted top MSHA officials to send Phillipson -- who had examined the crack, but not measured it, on July 28 -- back to the Upper Big Branch longwall section on Thursday.

In a report to his superiors, Phillipson described the crack as "a slab of floor rock cantilevered up as floor heave, which has formed an open aperture crack with brow parallel to the solid block of coal."

The crack runs for about 36 feet "outby" -- toward the mine's opening -- from the longwall section mining face, the geologist said. When it reaches a crosscut tunnel, the crack itself disappears, but the floor heaving continues for another 10 feet, the geologist said. The crack is about five inches deep and the floor heaving is six to 10 inches high, MSHA's geologist found.

Also, the geologist found that the crack is not "rooted," meaning it doesn't appear connected to the coal seam or a void below the active mining area, officials said.

"It wasn't a massive crack," Stricklin said. "It was what you would typically see in a longwall mine."

MSHA officials have not said the floor crack and similar smaller cracks are not evidence worth examining. Instead, they have disputed Massey's description of their size and the conclusions the company has drawn from the cracks' presence in the mine.

Such cracks and floor heaving is typically caused by the shifting of ground pressures during highly mechanized longwall mining, and can release methane from coal seams and geologic formations below.

Since early June, federal and state investigators have focused on, among other things, incidents in 2003 and 2004 when methane "outbursts" from the mine floor inundated the Upper Big Branch with the explosive gas. No ignitions or injuries were reported in those two incidents.

MSHA documents show Massey had proposed a number of steps, including de-gasification wells, to prevent a recurrence, and federal experts proposed additional measures, but MSHA has been unable to explain which of those steps were eventually implemented, and Massey has not responded to questions about the matter.

"There may be a crack in there that was involved in the explosion," Stricklin said, "but we don't know that yet."

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.