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Members of a federal panel investigating the cause of the Gulf of Mexico rig explosion and oil spill accused rig owner Transocean on Tuesday of thwarting their efforts to get to critical documents and a witness.

The co-chair of the panel, U.S. Coast Guard Capt. Hung Nguyen, told a crowded hearing room in a New Orleans suburb that members for two months have been trying to get Transocean to turn over materials related to its compliance with international safety management codes.

Nguyen said the panel, which is also looking for ways to improve safety and oversight, also has been unable to get a specific Transocean manager to testify about safety.

Transocean lawyers said the document request is too cumbersome and that whether the witness testifies isn't within their control.

Nguyen said one of the key elements the panel has been trying to analyze is the safety culture at the companies involved in the April 20 disaster. He said the panel will have to make recommendations whether or not Transocean supplies the information, so he encouraged them to comply.

"We did issue two subpoenas for the same thing. Each time we were told it was irrelevant and burdensome," Nguyen said. "If they are burdensome, that means there is something going on with your safety management system."

Another panel member, Coast Guard Capt. Mark Higgins, said the board has been "thwarted in some respect" in getting to the witness.

"I would encourage you to look at this as an opportunity to disprove what we have seen through this small window as to the culture at Transocean," Higgins said.

Transocean lawyer Ned Kohnke said the company has acted in good faith and produced everything it believes it should. He said the panel has the right to go to court to enforce the subpoena.

"How you can say we are thwarting is beyond me," Kohnke said.

He accused the board of making improper conclusions and not following its own rules of procedure.

"With all due respect, you have been wrong in other regards," Kohnke said. "We are here cooperating."

Later, another attorney accused Nguyen of being biased toward Transocean and insisted he remove himself from the panel. The request was denied.

Also Tuesday, two Transocean workers who were on the Deepwater Horizon at the time of the explosion and were responsible for monitoring the computer system that keeps the rig in place testified about the alarms that went off, the actions of personnel on the bridge and the effort to evacuate the crew. Yancy Keplinger said crew members received a call from the rig floor warning about a well control issue, but there was no time to react because the explosion occurred right after.

A third Transocean official testified that water poured onto the burning rig was meant to keep the vessel cool so it could be stabilized, not to put out the fire.

Who was responsible for fighting the fire and how prepared the companies were to respond have been key points of inquiry by the joint U.S. Coast Guard-Bureau of Energy Management, Regulation and Enforcement investigative panel.

Eleven workers were killed, and 206 million gallons of oil spewed from the well, according to federal estimates.

BP PLC's well a mile beneath the sea gushed for three months before being capped in July and then permanently sealed in September. The British oil giant owned the well but was leasing the rig that exploded from Transocean Ltd.

In other developments Tuesday:

— President Barack Obama signed a widely expected executive order establishing a Gulf Coast Restoration Task Force. The panel, which was recommended by Navy Sec. Ray , will be led by Environmental Protection Agency administrator Lisa Jackson. Obama's order asks the task force within a year to issue a strategy that will provide a roadmap for restoration efforts.

— It was announced that another portion of the Gulf was reopened to commercial and recreational fishing after federal scientists found no oil contamination to bar consumption of seafood. The 2,927 square-mile area is located off eastern Louisiana, about 40 miles south of the blown-out BP well.

Associated Press Writer Dina Cappiello contributed to this report from Washington.