Executives from BP and other companies involved in a deadly Gulf of Mexico offshore oil well blowout blamed each other in Washington on Tuesday as troops and prison inmates rushed to shore up Louisiana's coast against a huge oil slick.

The oil bosses were grilled on safety practices by members of the Senate Energy Committee, with committee chairman Jeff Bingaman saying it appeared the explosion on the Deepwater Horizon rig that triggered the oil slick was due to a "cascade of errors, technical, human and regulatory."

The hearings are set to continue on Wednesday, the same day a group of activists called Seize BP plans demonstrations at the company's offices and other sites across the U.S. to demand the government freeze its assets to ensure payment for the cleanup and compensation for those hurt by the spill. BP's stock ended down 0.67% in London and its American Depositary Receipts fell 0.12% in New York. The shares have fallen more than 15%t since the rig blast on April 20, wiping more than $30 billion from its market value.

White House spokesman Robert Gibbs said President Barack Obama is "deeply frustrated" that the oil leak in the Gulf has not yet been stopped three weeks after the blast. There are fears it could become the worst oil spill in U.S. history with staggering ecological and economic consequences for fisheries, beaches, wildlife and tourism in at least four states. BP spokesman Daren Beaudo said that some oil had begun washing on the Louisiana shoreline. Beaudo, who took reporters on a boat tour, said oil had washed ashore at three locations: Dauphin Island, Alabama; the Chandeleur Islands off Louisiana; and the South Pass-Port Eads area on a remote stretch of Louisiana's mainland.

"Well we are outside the South Pass of Louisiana where some of the first oil has impacted the shoreline. What we have behind is a forward staging area," he said as clean-up crews removed contaminated sand from the coast.

For some Gulf residents, life went on. Alabama residents were taking a "wait and see" approach to tar balls that washed up on the shore of a popular local beach on Dauphin Island, which government officials have not yet confirmed were linked to the spill.

"The water is pretty clear ... fishing is still good," angler Clyde Willis said.

The fight to contain the slick went on in Louisiana, Mississippi, Alabama and Florida, whose fishing and tourism industries are already feeling the pinch, while BP readied another potential subsea fix. But the U.S. government is concerned about whether enough protective booms are being provided to adequately defend the U.S. Gulf Coast shoreline from a massive oil spill, Homeland Security Secretary Janet Napolitano said on Tuesday.

"We have some concerns about getting adequate boom," she told reporters during a visit to Mobile, Ala., referring to the plastic barriers that are being strung along the coast to keep the oil off the shore. The accident's fallout is being felt on the regulatory front as the ruptured well keeps spewing at least 5,000 barrels (210,000 gallons/795,000 liters) of crude into the Gulf each day in what threatens to be the worst-ever U.S. oil spill.

In response, U.S. Interior Secretary Ken Salazar announced that the federal agency that oversees offshore drilling will be split in two to separate the collection of oil royalties from safety inspection duties. The explosion of the Transocean-owned and operated rig, which killed 11 workers, has governments at all levels scrambling to react. Obama has already suspended a plan to open up more waters to oil drilling.

Finger Pointing

In the congressional hearings, BP America President Lamar McKay, Transocean Chief Executive Steven Newman and Tim Probert, an executive at Halliburton, sat through senators' accusations, then pointed fingers at each other. McKay said the rig's blowout preventer, equipment designed to protect workers by cutting the flow of crude in the case of sudden changes in pressure, had been modified.

Indeed, modifications to the gear were made in 2005, but at BP's request, said Transocean's Newman. Republican Senator John Barrasso told the executives: "I hear one message and the message is: 'Don't blame me.' Well, shifting this blame does not get us very far."

Senator Ron Wyden, a Democrat, at one point interrupted McKay, saying, "The culture of this company has been one accident after another." BP had been trying to repair its image following a 2005 explosion at its Texas City refinery, which killed 15 workers.

Senator Barbara Boxer, a Democrat, slammed BP for stating before it began drilling the fateful well that it would use "proven technology" as it sought to get an exemption from an environmental assessment. After the accident, BP said it wasn't sure how the clean-up would go because the equipment had never been tested in deep water conditions.

"This is just unacceptable to say two starkly different things about the same project," Boxer told McKay. Halliburton joins BP and Transocean in the hot seat because it provided a variety of services on the rig and was involved in cementing the well to stabilize its walls and plug it.

Transocean pins the blast on the failure of the cementing to plug the well. BP leased the rig and operated the well. On their way into the hearings, the oil men were jeered by protesters holding signs saying "Boycott BP" and "BP Kills." BP will try covering the leak nearly a mile (1.6 km) under the surface with a much smaller funnel than the 98-ton dome it tried in vain to put in place over the weekend.

The so-called "top hat" dome is expected to be placed over the relentless leak on Thursday. Desperate efforts continued to protect the coastline, including fragile wetlands, from the approaching slick. In Port Fourchon, La., fatigue-clad Army National Guard troops from the 769th Engineer Battalion of Louisiana sweated alongside prisoners in scarlet red pants and white T-shirts with "Inmate Labor" on the back as they filled giant 1,000-pound (450-kg) sandbags. Black Hawk helicopters dropped the sandbags to plug gaps in coastal beaches through which the oil could seep.