MONTCOAL, West Virginia (AP) — A huge underground explosion blamed on methane gas killed 25 coal miners in the worst U.S. mining disaster in more than two decades. Four others were missing Tuesday, their chances of survival dimming as rescuers were held back by poison gases that accumulated near the blast site.

Rescuers prepared to drill three shafts going down over 1,000 feet (300 meters) each to release methane and carbon monoxide that chased them from the mine after the blast Monday afternoon, Gov. Joe Manchin said.

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West Virginia State Police direct traffic at the entrance to Massey Energy's Upper Big Branch Coal Mine Monday, April 5, 2010 in Montcoal, W.Va. (AP Photo/Jeff Gentner) ASSOCIATED PRESS

The site of the explosion Monday afternoon was about 1 1/2 miles (2 1/2 kilometers) into the sprawling Upper Big Branch mine. The mine, owned by Massey Energy Co., is about 30 miles (50 kilometers) south of Charleston.

Manchin said at an early morning news briefing that while drilling on at least one of the three holes was slated to begin soon, it would take perhaps 12 hours before the drilling was complete and rescue teams could be sure of their safety in the mine, meaning the search wasn’t expected to resume before 6 p.m. (2200 GMT).

“It’s going to be a long day and we’re not going to have a lot of information until we can get the first hole through,” Manchin said.

The drills need to bore through about 1,100 feet (335 meters) of earth and rock, he said.

“All we have left is hope, and we’re going to continue to do what we can,” Kevin Stricklin, an administrator for the federal Mine Safety and Health Administration, said at a news conference. “But I’m just trying to be honest with everybody and say that the situation does look dire.”

Though the cause of the blast was not known, the operation run by Massey subsidiary Performance Coal Co. has a history of violations for not properly ventilating highly combustible methane gas, safety officials said.

Stricklin said officials had hoped some of the missing survived the blast and were able to reach airtight chambers stocked with food, water and enough oxygen for them to live for four days. However, rescue teams checked one of two nearby and it was empty. The buildup of toxic methane gas — a constant problem at the mine — and of carbon monoxide prevented teams from reaching other chambers, officials said.

A total of 31 miners were in the area during a shift change when the blast happened, officials said. Some may have died in the blast and others when they breathed in the gas-filled air, Stricklin said. Eleven bodies had been recovered and identified, but the other 14 have not, said Manchin, who returned to the state after being out of town. Names weren’t released publicly, but Manchin said three of the dead are all members of the same family.

“Everybody’s just heartbroken over this and the impact on these families,” said mine safety director Joe Main, who was headed to West Virginia.

It is the most people killed in a U.S. mine since 1984, when 27 died in a fire at Emery Mining Corp.’s mine in Orangeville, Utah. If the four missing bring the total to 29, it would be the most killed in a U.S. mine since a 1970 explosion killed 38 at Finley Coal Co., in Hyden, Kentucky.

After a record low 34 deaths last year, Main said he and others believed coal mining had turned the corner on preventing fatal accidents.

“There’s always danger. There’s so many ways you can get hurt, or your life taken,” said Gary Williams, a miner and pastor of a church near the southern West Virginia mine. “It’s not something you dread every day, but there’s always that danger. But for this area, it’s the only way you’re going to make a living.”

In Monday’s blast, nine miners were leaving on a vehicle that takes them in and out of the mine’s long shaft when a crew ahead of them felt a blast of air and went back to investigate, Stricklin said.

They found nine workers, seven of whom were dead. Others were hurt or missing about a mile and a half inside the mine, though there was some confusion over how many. Others made it out, Manchin said.

In a statement early Tuesday, Massey Chairman and CEO Don Blankenship offered his condolences to the families of the dead miners.

“Tonight we mourn the deaths of our members at Massey Energy,” Blankenship said.

Massey Energy, a publicly traded company based in Richmond, Virginia, has 2.2 billion tons of coal reserves in southern West Virginia, eastern Kentucky, southwest Virginia and Tennessee. It ranks among the top five U.S. coal producers and is among the industry’s most profitable. It has a spotty safety record.

In the past year, federal inspectors fined the company more than $382,000 for repeated serious violations involving its ventilation plan and equipment at Upper Big Branch. The violations also cover failing to follow the plan, allowing combustible coal dust to pile up, and having improper firefighting equipment.

Methane is one of the great dangers of coal mining, and federal records say the Eagle coal seam releases up to 2 million cubic feet of methane gas into the Upper Big Branch mine every 24 hours, which is a large amount, said Dennis O’Dell, health and safety director for the United Mine Workers labor union.

In mines, giant fans are used to keep the colorless, odorless gas concentrations below certain levels. If concentrations are allowed to build up, the gas can explode with a spark roughly similar to the static charge created by walking across a carpet in winter, as at the Sago mine, also in West Virginia.

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Associated Press writers Allen G. Breed, Vicki Smith, Tom Breen and Tim Huber in West Virginia and Sam Hananel in Washington contributed to this report.

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