Rescuers drilled into a coal mine where 25 people died in an explosion but got no answer Wednesday when they banged on a pipe, trying to communicate with possible survivors.

Crews needed to bore at least one more hole to release poison gases before searchers could enter the Upper Big Branch mine to look for four people still missing in the worst U.S. mining accident in more than two decades.

The company that owns the mine, Massey Energy Co., frequently sidesteps hefty fines by aggressively contesting safety violations, including recent problems with the ventilation system that clears away combustible methane gas.

Methane was blamed for the explosion that rocked the mine Monday, and a dangerous buildup of that gas along with carbon monoxide prevented anyone from getting inside to pull out the bodies of 18 dead miners or to look for the four still unaccounted for.

Rescuers hoped they might somehow have reached a chamber where they could survive for four days. Seven bodies were pulled out after the explosion, and two miners were hospitalized.

Gov. Joe Manchin said the first hole reached the Upper Big Branch Mine after boring through about 1,090 feet of earth and rock. Rescuers banged on the drill pipe for 15 minutes in hopes of being heard below ground, but got no response.

Officials said they also plan to set off three small explosions on the surface to send a seismic signal to the mine.

Miners are trained to bang back on the drill's casing, Manchin said. Sections of mine roof contain numerous metal bolts that help keep it in place and that trapped miners can bang on to signal their presence.

Officials said they might need to drill as many as four holes to vent the mine, but Chris Adkins, chief operating officer for Massey, said Wednesday that two might be enough. Once rescuers can enter the mine it will take four or five hours to get far enough inside to check for survivors, who would be about 1,000 feet below the surface.

"We hope, we pray that the first two holes that go down will give us enough information to where we can pull the atmosphere back to where it is not explosive and get back in there," Adkins said.

The quality and quantity of coal produced at Upper Big Branch make the mine one of gems of Massey's operation. The mine produced more than 1.2 million tons of coal last year and uses the lowest-cost underground mining method, making it more profitable. The mine produces metallurgical coal that is used to make steel and sells for up to $200 a ton _ more than double the price for the type of coal used by power plants.

Federal regulators probing the explosion plan to review Massey's safety violations, many of which involved venting methane gas. If the odorless, colorless gas is not kept at safe levels, a small spark can ignite it.

Massey is still contesting more than a third of all its violations at the Montcoal, W.Va., mine since 2007. In the past year, federal inspectors have proposed more than $1 million in fines for violations at the mine. Only 16 percent have been paid.

Bombarding federal regulators with appeals is an increasingly common industry tactic since the 2006 Sago mine disaster that killed 12 led to stiffer fines and new enforcement to punish the worst offenders, according to an Associated Press review of records from the Mine Safety and Health Administration.

In an interview Tuesday with AP, Massey CEO Don Blankenship downplayed the link between the ventilation system and the accident.

"I don't know that MSHA thought there was a problem," he said.

The death toll in Monday's explosion was the highest in a U.S. mine since 1984, when 27 people 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 to die in a U.S. coal mine since a 1970 explosion killed 38 at Finley Coal Co. in Hyden, Ky.

In the area about 30 miles south of Charleston where coal is king, people anxiously awaited word on the missing.

Larry Asbury's son is on a mine rescue team. He joined about 50 mourners who packed the creaky pews of the modest St. Joseph Catholic Church a few miles from the disaster to honor the victims and pray that the missing turn up safe.

"The coal community is coming together and praying for miners and their families," he said. "It's just so important to show the community this kind of support."

Manchin said the first drill hole entered the section of the mine about a football field's length away from a rescue chamber where officials hope the miners sought refuge.

Searchers would have to navigate in the darkness around debris from structures shattered by the explosion and around sections of track that were "wrapped like a pretzel," said Kevin Stricklin, an administrator from the federal Mine Safety and Health Administration.

"There's so much dirt and dust and everything is so dark that it's very easy, as hard as it may seem to any of us outside in this room, to walk by a body," Stricklin said.

Manchin said he continues to meet with the families, but had no updates regarding the two injured miners pulled to the surface after the explosion.

"The families are very resilient," said the governor, flanked by state and federal safety officials. "They know the odds are against us."

Diana Davis said her husband, Timmy Davis, 51, died in the explosion along with his nephews, Josh Napper, 25, and Cory Davis, 20.

The elder Davis' son, Timmy Davis Jr., described his father as passionate about the outdoors and the mines. "He loved to work underground," the younger Davis said. Two other family members survived, he said.

During pauses at Tuesday's service at St. Joseph's, some leaned over and consoled each other.

"It's such a terrible time for West Virginia, but it's so important to ask for God's help," said Bishop Michael J. Bransfield.

Though the situation looked bleak, the governor pointed to the 2006 Sago Mine explosion that killed 12. Crews found miner Randal McCloy Jr. alive after he was trapped for more than 40 hours in an atmosphere poisoned with carbon monoxide.

___

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