NEW ORLEANS – A federal agency that oversees offshore oil drilling was so concerned about deaths and injuries it had documented that it was moving to impose new safety rules even before this week's oil rig explosion off the Louisiana coast, according to records obtained by The Associated Press.

A Minerals and Management Service review published last year found 41 deaths and 302 injuries out of 1,443 accidents, the majority caused by human error and operational and maintenance problems. The new rules focus on preventing human error, a safety area that hadn't received as much attention in the past.

The accidents and the explosion have again brought criticisms of the industry and opponents of President Barack Obama's plan for more offshore drilling say the collapse should be taken as a warning to slow the fervor to drill.

As officials continued to search for what caused the blast, crews were making progress cleaning up oil from the explosion Tuesday, and trying to contain what spilled and prevent any threat to the coast's fragile ecosystem. The Coast Guard was also using an airplane, a helicopter and a Coast Guard cutter to continue looking for 11 missing workers even as hopes diminished that they survived.

Officials did receive good news Friday when Coast Guard Rear Adm. Mary Landry said no oil appeared to be leaking from a well head at the ocean floor, nor was any leaking at the water's surface. But she said crews were closely monitoring the rig for any more crude that might spill out.

At midday Friday, at least half a dozen boats were visible with booms extended in loops, trapping a thin oil sheen that extended about 7 miles north of where the rig sank.

From the air, there was no sign the oil was affecting animal life in the area.

Strong winds were blowing generally from the south as a cold front approached from Texas. The passage of the front late Friday or Saturday was expected to shift winds to the north, which could push the sheen away from the coast.

BP PLC, which leased the rig and took the lead in the cleanup, said it has activated an extensive oil spill response, including using remotely operated vehicles to assess the well and 32 vessels to mop up the spill.

BP Chief Executive Tony Hayward said the company will do "everything in our power to contain this oil spill and resolve the situation as rapidly, safely and effectively as possible."

Weather forecasts indicate the spill was likely to stay well away from shore at least through the weekend, but if winds change it could come ashore faster, said Doug Helton of the National Oceanic and Atmospheric Administration's office of response and restoration.

Environmentalists said the explosion was a reminder the industry was dangerous.

"I would hope it would serve as another wake-up call on this issue that there is no such thing as safe oil drilling," said Sara Wan, a California Coastal Commission who opposes offshore drilling. "Once that oil starts leaking in the ocean, that damage is irreversible. You just look at what happened with Exxon-Valdez — they're still feeling the affects of it. There's no real way to clean it up."

Despite the explosion, White House spokesman Robert Gibbs said the president had no plans to give up his effort to expand offshore drilling. Gibbs said Obama continues to believe that the United States needs a comprehensive solution to its energy problems — including expanded domestic production of oil and natural gas short term personal loans.

The president still believes increasing domestic oil production can be done safely, securely and without harming the environment, Gibbs said.

"I don't honestly think it opens up a whole new series of questions, because, you know, in all honesty I doubt this is the first accident that has happened and I doubt it will be the last," Gibbs said.

Meanwhile, U.S. Sen. Bill Nelson called for a congressional investigation of safety practices at offshore oil rigs. Nelson, a Democrat who has led opposition to offshore drilling, said he asked the U.S. Interior Department to investigate and provide a comprehensive report on all U.S. drilling accidents over at least the last decade.

"The tragedy off the coast of Louisiana shows we need to be asking a lot more tough questions of big oil," Nelson said. "I think we need to look back over 10 years or so to see if the record denies the industry's claims about safety and technology."

The Coast Guard, which was leading the investigation, had not given up the search early Friday for those missing from the rig.

Lt. Cmdr. Cheri Ben-Iesau said a Coast Guard cutter would remain on the scene Friday after searching overnight, and a helicopter would take advantage of clear weather to make three more search flights.

"We use a scientific program to make a best-guess estimate on survivability," Ben-Iesau said. "And then the Coast Guard searches a little longer than that. Because there's always the unknown."

Carolyn Kemp of Monterey, La., said her grandson, Roy Wyatt Kemp, 27, would have been on the drilling platform when it exploded.

"They're assuming all those men who were on the platform are dead," Kemp said. "That's the last we've heard."

Most of the crew — 111 members — were ashore, including 17 taken to hospitals. Four were in critical condition. Four others made it off safely were still on a boat operating one of several underwater robots being used to assess whether the flow of oil could be shut off at a control valve on the sea floor, said Guy Cantwell, spokesman for rig owner Transocean Ltd.

Ed Overton, a Louisiana State University environmental sciences professor, said the sheen's distance from shore means the impact on wildlife is likely not widespread, although some seabirds that dive for food could become coated with oil.

The problem, Overton said, would be if thicker globs of oil reach coastal areas such as the Chandeleur islands, home to hatcheries for pelicans and other birds.

A turn in winds and currents might send oil toward fragile coastal wetlands — nurseries for fish and shrimp and habitat for birds.

To prevent that, the Marine Spill Response Corp., an energy industry cleanup consortium, brought seven skimmer boats to suck oily water from the surface, four planes that can scatter chemicals to disperse oil, and 500,000 feet — 94.6 miles — of containment boom, a floating barrier with a skirt that drapes down under the water and corrals the oil.

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Schwartz reported from Los Angeles. Associated Press writers Holbrook Mohr from Jackson, Miss., Mike Kunzelman, Cain Burdeau and Alan Sayre in Louisiana, Chris Kahn in New York, Jason Dearen in San Francisco and Sofia Mannos of AP Television News contributed to this report.

Oil drilling accidents prompted new safety rules