(CNN) -- A "perfect storm was brewing" in West Virginia's Upper Big Branch coal mine in the weeks and days before a fireball tore through it on April 5, 2010, killing 29 miners and injuring one severely, according to a just-released report by the Governor's Independent Investigation Panel.
The report describes in vivid detail the conditions at Upper Big Branch before, during and after the deadliest U.S. mine disaster in 40 years, and concludes that the explosion was preventable and resulted from "failures in safety systems" at the mine in southern West Virginia.
The findings are based on physical examinations of the mine, regulatory records, the mine's internal records and more than 300 interviews with current and former mine employees, family members of miners, as well as with state and federal mine regulators. Noticeably absent from the 120-page report: testimony from the top people in charge of the mine. They invoked their Fifth Amendment privilege against self-incrimination and refused to cooperate with investigators.
Among the key findings: The Upper Big Branch mine lacked adequate ventilation, water sprays on equipment were not properly maintained and failed to function as they should have, and the mining company didn't meet federal and state safety standards for the application of rock dust, a crucial tool in keeping highly explosive coal dust inert.
How far short did they fall? Citing internal mining reports, the investigation found that in the 26 days before the disaster, rock dusting was carried out at the Upper Big Branch mine just 11.6% of the time it was requested. Out of 561 dustings requested, only 65 were recorded. The report notes that "extensive tests conducted by the (Mine Safety and Health Administration) after the disaster support miners' testimony that the Upper Big Branch mine was poorly dusted" and also says "a well dusted mine would have put the brakes on a propagating explosion and the death toll would have been significantly less."
Massey Energy maintains the explosion was caused by an unforeseen, massive influx of methane or natural gas. But the report rejects that argument, calling the disaster man-made and blaming a corporate "culture in which wrongdoing became acceptable, where deviation became the norm."
The report says insufficient basic safety measures at Upper Big Branch turned a small fireball into "an enormously powerful blast" that rocketed through more than 2 1/2 miles of the mine, nearly 1,000 feet underground.
While officials with the U.S. Department of Labor and its Mine Safety and Health Administration have repeatedly defended the agency's performance, the panel's investigators reached a much different conclusion.
"Despite MSHA's considerable authority and resources, its collective knowledge and experience, the disaster at the Upper Big Branch mine is proof positive that the agency failed its duty as the watchdog for coal miners," the report said.
There was no immediate comment from MSHA Thursday.
The panel was commissioned days after the Upper Big Branch explosion by West Virginia's then-Gov. Joe Manchin, and its report draws extensively on testimony given under oath.
According to investigators, Brent Racer had just entered the mine to begin his shift when the explosion hit.
"... it felt like sand picking up, you know, like at the beach, pinging you in the face when it starts blowing real hard. And you couldn't hear the belt, and all of a sudden you heard this big roar, and that's just when the air picked up. I'd say it was probably 60-some miles per hour. Instantly black. It took my hardhat and ripped it off my head, it was so powerful."
Racer was one of the last men to make it out alive.
Adam Jenkins, who was directing traffic in and out of the mine when disaster struck, testified about what he saw on the mine's surface.
"All the dust started, just a white smoke started pouring out the portals, and it sounded like thunder. It was constant. And I didn't know what happened. And [mine superintendent] Gary May, he said, 'Oh, Lord ... something bad's happened.' He said to get ahold of everybody and tell them to get outside now. And I hollered and hollered and hollered for over a half hour."
Roof bolter Tim Blake, who was ending his shift when the blast hit, described putting on his emergency breathing equipment and trying to help eight fallen miners who were with him, including a large man nicknamed Pee Wee.
"I had to manhandle him, get him down, lay him flat down. I put his rescuer (breathing equipment) on him. I went to the next man, which was the boss [Steve Harrah], and he was laying face down. ..I had to roll him over, put his rescuer on him."
The men were being overtaken by carbon monoxide. Blake realized his fresh air supply was running out and checked on his friends one last time before leaving the mine.
"So I went around to each man again, felt for a pulse. Everybody had a pulse but one man. I couldn't find no pulse on him."
Of those seven miners who were still alive when Blake left them, just one survived. Leaving his friends behind, Blake testified, "was the hardest thing" he ever did.
In a statement, Massey Energy's general counsel Shane Harvey told CNN the company is reviewing the report carefully.
He said Massey Energy agrees that the industry needs to examine whether it can achieve better methane monitoring technology.
"At UBB, all methane monitors were functional and yet the mine experienced a massive inundation of methane-rich natural gas that was not detected in time to prevent the explosion," he said. "We have been examining where improvements in methane monitoring can be made and we hope to develop some better technologies as a result of our investigation."
Shane said the company disagrees with the report's conclusion that the explosion was fueled by coal dust. "Again, we believe that the explosion was caused by a massive inundation of methane-rich natural gas. Our experts feel confident that coal dust did not play an important role."
Watch Anderson Cooper 360° weeknights 10pm ET. For the latest from AC360° click here.