STEVE INSKEEP, Host:
It's MORNING EDITION, from NPR News. I'm Steve Inskeep.
RENEE MONTAGNE, Host:
Howard, good morning.
HOWARD BERKES: Good morning.
MONTAGNE: What did investigators say about this deadly accident - how it started?
BERKES: Now problem number two, a water spraying system that's supposed to help control sparks wasn't working. Now investigators point out that the water sprayers also help control coal dust, which is explosive. The sparks ignited the methane in what is described as a small fireball. But without the sprayers to control or extinguish that ignition and with coal dust to fuel it, it exploded. Investigators reported excessive coal dust spread throughout the mine and that fed the blast, sending it coursing more than two miles underground.
MONTAGNE: It sounds like a lot of things went wrong in this Massey Energy mine. Did investigators explain that?
BERKES: Now, some people did ask about federal oversight - were regulators doing enough? And the officials said regulators cited the mine repeatedly, they closed unsafe areas at times but Massey Energy would fix the problem so they could start cutting coal again and the violations would return.
MONTAGNE: And Howard, we're calling this a working theory. Does that mean that there is some uncertainty about what went wrong?
BERKES: I'm told that investigators were careful not to say that this is their final and firm conclusion. They're still working through evidence and it'll be 60 to 90 days, they said, before they'll have a final report. They also pointed out that there's a federal criminal investigation that's still underway. And by the way, the investigators themselves will talk publicly about their tentative findings in a news conference later this morning.
MONTAGNE: And any response so far from the owner of the Upper Big Branch mine, Massey Energy?
BERKES: Massey is set to conduct its own briefing for the families Friday morning in Charleston, West Virginia. And the company has had its own theory - based essentially on a natural and massive infusion of methane or natural gas that overwhelmed all the safety systems. Last night, one of the government's experts refuted that theory by presenting evidence he said contradicts it. We'll get Massey's response to that and the rest of the government's tentative conclusions I'm sure on Friday.
MONTAGNE: Howard, thanks very much.
BERKES: You're welcome, Renee.
MONTAGNE: NPR's Howard Berkes reporting from Beckley, West Virginia.