A 36-foot crack in the Upper Big Branch mine isn't venting methane and didn't contribute to a blast in April that killed 29 men, a federal official said Friday, disputing a company's claim that the crack could've caused of the blast.

The crack has been the subject of a running dispute between the Mine Safety and Health Administration and the mine's owner, Virginia-based Massey Energy. Company officials have suggested a massive crack could have unexpectedly flooded the southern West Virginia mine with explosive methane gas.

Ruling out any possible contributing factors at this point in the investigation is "completely irresponsible," company spokesman Jeff Gillenwater said in an e-mail.

"No one investigating the tragedy at UBB should rush to judgment," he said, insisting the crack merits further investigation.

Some of the victims' relatives said Massey told them the crack was 150 feet long. Stricklin strongly disputed that in a media briefing earlier this week but couldn't offer an exact measurement.

Stricklin said he sent a geologist underground to measure the crack for a second time Thursday. The crack — near the longwall mining machine and a number of other, smaller cracks — was 36 feet long about 5 inches deep, he said. Investigators believe the April 5 explosion occurred in an area near the machine.

But the geologist said the crack in the sandstone floor was "rootless," meaning it did not lead to a coal seam, and was not venting methane, Stricklin said.

Cracks and floor heaving are common in longwall mining, he said, and this one had no special significance.

Stricklin wouldn't rule out another crack elsewhere in the mine causing the blast.

"I just didn't want a family member thinking this particular crack was the cause of the explosion," he said. "I didn't want the question lingering out there."

Stricklin also insisted earlier this week that all explosions are preventable. Even if a massive inundation of methane occurred, he said, it should not have automatically exploded.

Mines should have enough fresh air movement to carry methane out, the equipment underground should not be able to provide a spark, regular inspections should find flaws in any safety systems, and all mines should be thoroughly coated with rock dust to prevent coal dust from exploding.

"Those are four key components we stand by," Stricklin said. "We don't think explosions need to occur anywhere."