Much of the area is dotted with giant pillars of coal, left standing in a checkerboard pattern to hold up the mountain above the Eagle coal seam and prevent the mine's ceiling from collapsing.

A map plotting where rescuers found the bodies of victims shows the blast spread north, east, south and west simultaneously, and repeatedly turned 90-degree corners when it encountered coal pillars and passageways.

Experts say that's precisely how explosions behave in the confined space of a mine -- if fuel is available.

"The best way to describe it, it follows the source of fuel," said Michael Sapko, who studies coal mine explosions at the National Institute for Occupational Safety and Health, the government's chief mine safety research organization.

Mines use complex ventilation systems powered by enormous fans to push fresh air in and methane out. Experts say the effect is usually a breeze ranging from mild to stiff.

Since the 1920s, mines have also been required to use pulverized rock to cover coal dust with a protective layer of inert material.

In a properly dusted coal mine, Sapko said, an explosion can be stopped almost in its tracks. But research by Sapko's agency shows even the thinnest coating of coal dust is dangerous enough to instantly transform a small explosion into a giant one.

"Once it gets in the air, and if there's an ignition source present, it's uncontrollable at that time," Sapko said.

Months of examination reports written by Massey employees and years of violations cited by federal inspectors indicate Upper Big Branch miners routinely struggled to keep the mine dusted.

MSHA records show inspectors have slapped Massey with at least 475 citations, including not having enough rock dust to prevent explosions and allowing combustible materials pile up at Upper Big Branch since it opened in 1994.

One of the most serious came less than a month before the explosion. During a routine inspection, MSHA scooped up eight samples and sent them to a lab to make sure they contained enough rock dust.

Lab tests determined one of the samples contained less noncombustible material than required by law, according to a citation issued eight days after the explosion.

MSHA rated the mid-March dust violation "significant and substantial," saying it was "reasonably" likely to cause a fatal accident if not corrected.

"This standard/condition has been cited 8 times in the last two years," an unnamed MSHA employee wrote as justification on a form dated April 13.

The samples came from a spot called Headgate 22, an area that was being prepped as the next section to be mined using Massey's longwall mining machine. It was about three miles from the nearest entrance.

"Needs dusted," says a report from that area earlier in the day April 5.

The problem was reported, but there's no indication it was fixed.

The final notation in the record book for Headgate 22 notes small concentrations of methane in four locations and the same problem with one of them: "Needs Dusted."

BECKLEY, W.Va. -- About the time Michael Elswick was wrapping up work deep inside the Upper Big Branch mine, he phoned a colleague on the surface with an ominous if relatively routine report.

Three conveyer belts needed to be sprinkled with pulverized stone to cover a layer of combustible coal dust and reduce its danger, the veteran coal miner said, according to a copy of a log book The Associated Press obtained through an open records request.

Just 32 minutes later, Elswick and 28 other men were dead.

Authorities say they died instantly in an April 5 explosion that investigators suspect began with methane, then gorged on coal dust as it turned 90-degree corners, rounded a 1,000-foot-wide block of coal and built enough force to kill men more than a mile away.

The information Elswick and his co-workers dutifully recorded in the hours, weeks and months before the worst coal mining disaster in 40 years shows it struck in what could be considered a predictable place: A mine with a chronic, stubborn coating of coal dust, which can make a minor flare-up much, much worse.

According to the log book, provided to the AP by the West Virginia Board of Coal Mine Health and Safety, Elswick's co-worker Scott Halstead reported problems with five of the six belts he inspected the day of the explosion. The reports show the need for rock dust along belts stretching more than three miles underground in the southern West Virginia mine owned by Massey Energy Co.

Elswick called the surface at 2:30 p.m. with the latest safety update. Most workers were getting ready to head to the surface and home to their families. It was the day after Easter.

Elswick, Halstead and others had made similar reports for months, noting that vast areas of the mine needed rock dusting. And shift after shift, they reported that the problem areas had been treated.

But the page that would list corrective actions taken for the issues Elswick and Halstead reported that afternoon is blank. Shane Harvey, Massey's general counsel, conceded the problems probably could not have been fixed between Elswick's call and the time of the blast.

However, Harvey said the log book observations are meant as more of a reminder than as a cause for concern.

"You make a notation of it so that it gets done, and the fact that a notation was made doesn't mean it was a problem," Harvey said. "That's the way the company looks at it. Just like you'd make notations, at least mental notations, to vacuum your floor."

Officially, the cause of the Upper Big Branch disaster remains undetermined. But 10 days after the explosion, in a preliminary report to President Barack Obama, the federal Mine Safety and Health Administration blamed a combination of methane gas and coal dust.

Massey is pushing a far different scenario -- one that potentially relieves the company of blame and pushes responsibility onto MSHA. Massey claims millions of cubic feet of methane rushed in from a floor crack and overwhelmed the ventilation system weakened by MSHA-mandated changes and other safeguards.

Regulators have disclosed that gas detectors sensed explosive amounts of methane inside the mine at the time of the blast. But they've kept most other details secret.

Massey officials insist coal dust had nothing to do with the tragedy, citing feedback from personnel who have been inside Upper Big Branch since the disaster. The mine "appears to have been very well rock dusted, with rock dust still in place," Harvey said.

And an explosion does not need coal dust to turn corners, Massey board member and mining engineer Stan Suboleski said.

"Maybe it was just a lot of methane," he said.

But thousands of pages of handwritten reports support the government's suspicions.

People who have been inside the mine since the blast continue to be stunned at the destruction. Former MSHA chief J. Davitt McAteer, who's conducting an independent investigation for Gov. Joe Manchin, said the explosion spread across more than two miles, packing lethal power most of the way.

Much of the area is dotted with giant pillars of coal, left standing in a checkerboard pattern to hold up the mountain above the Eagle coal seam and prevent the mine's ceiling from collapsing.

A map plotting where rescuers found the bodies of victims shows the blast spread north, east, south and west simultaneously, and repeatedly turned 90-degree corners when it encountered coal pillars and passageways.

Experts say that's precisely how explosions behave in the confined space of a mine -- if fuel is available.

"The best way to describe it, it follows the source of fuel," said Michael Sapko, who studies coal mine explosions at the National Institute for Occupational Safety and Health, the government's chief mine safety research organization.

Mines use complex ventilation systems powered by enormous fans to push fresh air in and methane out. Experts say the effect is usually a breeze ranging from mild to stiff.

Since the 1920s, mines have also been required to use pulverized rock to cover coal dust with a protective layer of inert material.

In a properly dusted coal mine, Sapko said, an explosion can be stopped almost in its tracks. But research by Sapko's agency shows even the thinnest coating of coal dust is dangerous enough to instantly transform a small explosion into a giant one.

"Once it gets in the air, and if there's an ignition source present, it's uncontrollable at that time," Sapko said.

Months of examination reports written by Massey employees and years of violations cited by federal inspectors indicate Upper Big Branch miners routinely struggled to keep the mine dusted.

MSHA records show inspectors have slapped Massey with at least 475 citations, including not having enough rock dust to prevent explosions and allowing combustible materials pile up at Upper Big Branch since it opened in 1994.

One of the most serious came less than a month before the explosion. During a routine inspection, MSHA scooped up eight samples and sent them to a lab to make sure they contained enough rock dust.

Lab tests determined one of the samples contained less noncombustible material than required by law, according to a citation issued eight days after the explosion.

MSHA rated the mid-March dust violation "significant and substantial," saying it was "reasonably" likely to cause a fatal accident if not corrected.

"This standard/condition has been cited 8 times in the last two years," an unnamed MSHA employee wrote as justification on a form dated April 13.

The samples came from a spot called Headgate 22, an area that was being prepped as the next section to be mined using Massey's longwall mining machine. It was about three miles from the nearest entrance.

"Needs dusted," says a report from that area earlier in the day April 5.

The problem was reported, but there's no indication it was fixed.

The final notation in the record book for Headgate 22 notes small concentrations of methane in four locations and the same problem with one of them: "Needs Dusted."