This MSHA photo shows what agency investigators say is inadequate water spray as the result of missing spray nozzles  on the longwall shearer at the Upper Big Branch Mine.

U.S. Mine Safety and Health Administration officials spent a little more than an hour earlier today briefing the media on their investigation of Massey Energy’s Upper Big Branch Mine Disaster, releasing information similar to what they provided to the disaster victims’ families last evening.

In addition, if you check the Upper Big Branch “Single Source Page” on the MSHA Web site, you’ll see that the agency posted some additional information, including a Power Point presentation (see here or here) that was provided to the families and some videos.

Kevin Stricklin, MSHA’s coal administrator, told us that agency investigators believe “the most likely”ignition source was the longwall machine’s cutting tool, or shearer. MSHA’s conclusion at this point is that a pocket of methane somehow seeped into the longwall area and was ignited by a spark created when a well-worn bit on the shearer hit a piece of rock as it cut into the coal. Stricklin said:

We’re going to need a little more time to be definitive, but the most likely source right now to the investigation team is the longwall shearer.

MSHA believes that a rather small methane ignition then turned into a major explosion, as it followed fuel — in the form of coal dust — through the mine’s underground tunnels.  MSHA repeated its previous conclusions that roughly 80 percent of the samples taken in the mine showed inadequate levels of crushed stone, or “rock dust”, meant to control explosive coal dust.  This time, MSHA also released a detailed map that shows where these samples were taken (click on it to make it bigger):

Now, Massey issued this statement a while after MSHA had concluded its briefing:

Massey representatives were not present at MSHA¹s family briefing or press conference, nor were Company officials briefed by MSHA on the issues they covered. Based on media accounts, however, we have some understanding of MSHA¹s working theory.

Our findings are different than MSHA¹s working theory, as we understand it. We do not currently believe that there were issues with the bits or the sprays on the shearer that contributed to the explosion. We likewise do not believe that coal dust played a meaningful role in the explosion. We currently believe the mine was well rock dusted and that the mine exploded due to an infusion of high levels of natural gas.

We plan on discussing our findings with the UBB families as soon as possible and we will brief the media in more detail at a later date. We are also very interested in meeting with MSHA officials to understand their conclusions.

But MSHA released a photo showing one of the worn-out longwall shearer bits:

And, MSHA released a video showing its test of the water sprays on the longwall shearer:

And the agency also posted this NIOSH video that discusses the ways explosions like this can occur and how they can be prevented:

MSHA officials also said their probe has so far found no evidence of flame or coking — evidence of a larger explosion — in the tailgate end of the longwall face. Government investigators believe that is strong evidence that a smaller ignition took place there, as opposed to the huge methane explosion Massey argues occurred (the tailgate end of the longwall face is where the famous floor crack Massey has made so much of is located).

Given the condition of the longwall shearer at Upper Big Branch, NPR’s Howard Berkes asked perhaps the most important question of the day: How is it possible that these conditions were allowed to exist if MSHA — as agency officials like to say — is using all of its available tools to inspect and take enforcement actions to protect miners?

Kevin Stricklin defended his agency’s inspectors, noting the large number of citations and serious enforcement orders issued at UBB:

Based on the numbers I’ve seen, I think my folks were enforcing the law here.

And MSHA chief Joe Main repeated another now-stock answer whenever the agency is questioned about why its enforcement efforts weren’t enough to prevent mining deaths, saying the ultimate responsibility for safety and health rests with the mine operator.

Other items of interest from the MSHA briefing:

— Agency investigators are looking into comments from a family member at last night’s meeting who said they personally overheard a call from the longwall section workers to the surface at about 3 p.m. on April 5 — just minutes before the explosion — that, if it happened, may shed some light on events underground.

— MSHA believes that, shortly before the explosion, power and water to the longwall machine were cut off by workers — and that at least two workers appeared to be trying to exit the longwall shearer area, making it about halfway down the face before the explosion occurred.

— In response to an interesting question from Dennis Roddy of the Pittsburgh Post-Gazette, Stricklin said that turning off water to the longwall would not have been the best idea if the miners had experienced an ignition — but that it appears to have been standard practice at Upper Big Branch to turn off the water whenever the power was turned off.

— Massey’s official mine progress map was not up to date, and MSHA investigators are looking into “remnants” of various types of ventilation controls that may or may not have been plotted on the map and may or may have not been part of the company’s approved ventilation plan.

— MSHA investigators are still actively looking into what went on at the mine over the Easter weekend, especially in the midnight shift prior to the explosion, trying to determine among other things if any ventilation changes were being made during that time.

Here’s the audio of the entire MSHA media briefing: