Read more at Coal Tattoo.

CHARLESTON, W.Va. -- More than three-quarters of the samples taken from Massey Energy's Upper Big Branch Mine did not comply with existing standards for controlling the buildup of explosive coal dust underground, federal investigators have revealed.

This potentially key evidence, first revealed to families of the mine disaster victims Thursday night, supports the theory that a buildup of coal dust might have made a methane ignition at Upper Big Branch far worse than it otherwise would have been.

During a Friday morning media briefing, U.S. Mine Safety and Health Administration officials said 79 percent of the more than 1,800 dust samples taken at Upper Big Branch exceeded federal limits for the allowable "combustible content."

MSHA officials were measured in their public remarks about the samples, saying further analysis is still needed and a final conclusion cannot yet be reached about the role of coal dust in the April 5 explosion that killed 29 miners.

"It's going to be fair to say that coal dust played a role," MSHA coal administrator Kevin Stricklin told reporters, "but we don't know how big of a role."

Massey Energy quickly challenged the MSHA data, calling it "unproven or faulty," and noted that the agency lost a major case over dust sampling following the deaths of 13 miners in an Alabama explosion nearly a decade ago.

"MSHA's narrow-minded focus on compromised coal-dust evidence is doing a disservice to those UBB families entitled to concrete answers unequivocally supported by accurate scientific findings and the facts," the company responded.

The coal-dust sampling data was, by far, the biggest news to emerge from MSHA's Thursday evening meeting with Upper Big Branch families and a Friday morning media briefing, both held as the investigation into the worst U.S. coal-mining disaster in 40 years continued into its sixth month.

Among other news from the MSHA briefing and the earlier meeting with miners' families:

| Investigators have interviewed at least 235 witnesses and have another 20 witnesses on their list for future closed-door sessions. MSHA has not decided if it will seek to question Massey CEO Don Blankenship.

| Massey managers have sent a letter to the West Virginia Office of Miners Health, Safety and Training that challenges subpoenas issued to company officials by the state. Among other things, Massey has objected to MSHA officials taking part in interviews conducted under the authority of state agency subpoenas. Under federal law, MSHA would be able to subpoena witnesses itself only if federal officials decided to hold such sessions in a public hearing.

| Methane detectors indicate the time of the explosion was somewhere between 2:59 p.m. and 3:06 p.m., but MSHA believes other monitors indicate the exact time was 3:02 and 40 seconds. MSHA officials told family members that clocks on the mine's carbon monoxide alarms -- which indicated a potential time for the explosion was 3:08 p.m. -- were off by a few minutes.

Read more at Coal Tattoo.

CHARLESTON, W.Va. -- More than three-quarters of the samples taken from Massey Energy's Upper Big Branch Mine did not comply with existing standards for controlling the buildup of explosive coal dust underground, federal investigators have revealed.

This potentially key evidence, first revealed to families of the mine disaster victims Thursday night, supports the theory that a buildup of coal dust might have made a methane ignition at Upper Big Branch far worse than it otherwise would have been.

During a Friday morning media briefing, U.S. Mine Safety and Health Administration officials said 79 percent of the more than 1,800 dust samples taken at Upper Big Branch exceeded federal limits for the allowable "combustible content."

MSHA officials were measured in their public remarks about the samples, saying further analysis is still needed and a final conclusion cannot yet be reached about the role of coal dust in the April 5 explosion that killed 29 miners.

"It's going to be fair to say that coal dust played a role," MSHA coal administrator Kevin Stricklin told reporters, "but we don't know how big of a role."

Massey Energy quickly challenged the MSHA data, calling it "unproven or faulty," and noted that the agency lost a major case over dust sampling following the deaths of 13 miners in an Alabama explosion nearly a decade ago.

"MSHA's narrow-minded focus on compromised coal-dust evidence is doing a disservice to those UBB families entitled to concrete answers unequivocally supported by accurate scientific findings and the facts," the company responded.

The coal-dust sampling data was, by far, the biggest news to emerge from MSHA's Thursday evening meeting with Upper Big Branch families and a Friday morning media briefing, both held as the investigation into the worst U.S. coal-mining disaster in 40 years continued into its sixth month.

Among other news from the MSHA briefing and the earlier meeting with miners' families:

| Investigators have interviewed at least 235 witnesses and have another 20 witnesses on their list for future closed-door sessions. MSHA has not decided if it will seek to question Massey CEO Don Blankenship.

| Massey managers have sent a letter to the West Virginia Office of Miners Health, Safety and Training that challenges subpoenas issued to company officials by the state. Among other things, Massey has objected to MSHA officials taking part in interviews conducted under the authority of state agency subpoenas. Under federal law, MSHA would be able to subpoena witnesses itself only if federal officials decided to hold such sessions in a public hearing.

| Methane detectors indicate the time of the explosion was somewhere between 2:59 p.m. and 3:06 p.m., but MSHA believes other monitors indicate the exact time was 3:02 and 40 seconds. MSHA officials told family members that clocks on the mine's carbon monoxide alarms -- which indicated a potential time for the explosion was 3:08 p.m. -- were off by a few minutes.

| MSHA officials said they are looking into what role the opening and closing of air-lock doors in the Upper Big Branch tunnels might have played in changing the flow of fresh air underground.

| Investigators are still looking into potential connections between the April 5 explosion and cracks discovered in the Upper Big Branch Mine floor. MSHA officials told family members that they have not been able to find any evidence that ventilation changes were made to control potential methane outbursts from the mine floor similar to those that occurred in 2003 and 2004.

With their release of the coal-dust data from Upper Big Branch, MSHA made public one of its most significant clues as to what might have sent the massive explosion rocketing through the Raleigh County mine, causing major damage across a 2 1/2-mile area underground.

Methane and coal dust are explosive and are created during the process of mining coal underground, but methane ignitions often can be smaller and less damaging, whereas a coal-dust explosion can rip through huge swaths of underground workings in an instant.

Under federal law, mine operators must spread crushed limestone, called "rock dust" across walls and other surfaces in underground tunnels to keep coal dust from igniting. The law requires operators to regularly "rock dust" to maintain the level of "incombustible" dust underground at a safe level.

Investigators at Upper Big Branch gathered dust samples from areas throughout the underground mine, and have analyzed those to determine if they comply with federal standards -- 65 percent in general, but 85 percent in "return" tunnels where dirty air is more likely to be present.

During Friday's media briefing, Stricklin said the samples taken weeks after the explosion at Upper Big Branch likely would overstate the compliance rate in Massey's favor.

As the explosion tore through mine tunnels, Stricklin said, it would burn up some of the combustible materials in mine dust, making the incombustible rock dust that was left appear to be a higher percentage of the total material present prior to the blast.

That was among the arguments MSHA made when it lost a lawsuit over the September 2001 explosion that killed 13 workers at the Jim Walter Resources No. 5 Mine in Brookwood, Ala.

In that case, Jim Walter appealed a citation in which MSHA blamed the explosion, in part, on the company's failure to properly rock-dust the No. 5 Mine. MSHA had based the citation on rock-dust samples taken after the explosion.

However, an administrative law judge with the Federal Mine Safety and Health Review Commission ruled that the post-explosion samples did not accurately reflect conditions in the mine prior to the blast. In a November 2005 ruling, Judge David F. Barbour ruled that the forces of the explosion probably had churned up more coal dust and blown rock dust around inside the mine. Barbour also noted that the No. 5 Mine had been flooded after the explosion to extinguish underground fires, and that the flooding probably had washed away some rock dust. Barbour also was unconvinced by additional testing of the coke content of the samples, which MSHA had argued helped show the rock-dusting samples were accurate.

This week, MSHA officials did not respond to questions about what changes they had made in their rock-dust sampling procedures since the Jim Walter case.

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