(CNN) -- Government scientists Tuesday increased the estimate of oil flowing into the Gulf of Mexico to between 35,000 and 60,000 barrels per day, up to 50 percent more than previously estimated. That translates into 1.5 million gallons to 2.5 million gallons per day.

The government's previous estimate, issued last week, was 20,000 to 40,000 barrels per day.

The change was "based on updated information and scientific assessments," and was reached by Secretary of Energy Steven Chu, Secretary of the Interior Ken Salazar, and Chair of the National Incident Command's Flow Rate Technical Group Marcia McNutt, the Deepwater Horizon Incident Joint Information Center said.

"The improved estimate is based on more and better data that is now available and that helps increase the scientific confidence in the accuracy of the estimate," it said.

Full coverage of Gulf oil disaster

Alberto Alisedo, a member of the flow rate technical group, said scientists reached the consensus after a three-hour conference call on Monday and a 10-hour meeting on Sunday of the group in Seattle, Washington.

"Our response to the spill is not determined by flow rate estimates," said BP spokesman Toby Odone. "Our primary concern is to capture as much oil as possible. We are building options to contain higher volumes of oil."

He called measurement of the flow rate "extremely challenging," given the fact that the leak is a mile below the surface of the water.

Tuesday night, President Obama used his first Oval Office address to the nation to say 90 percent of the oil gushing into the Gulf of Mexico will be captured within weeks.

Read full transcript of Obama's speech

"Already, this oil spill is the worst environmental disaster America has ever faced. And unlike an earthquake or a hurricane, it's not a single event that does its damage in a matter of minutes or days," the president told the nation. "The millions of gallons of oil that have spilled into the Gulf of Mexico are more like an epidemic, one that we will be fighting for months and even years."

In an attempt to counter complaints of a sluggish government response to the oil disaster, Obama noted cited resources have poured into the region including nearly 30,000 people working in four states to contain and clean up the oil.

"From the very beginning of this crisis, the federal government has been in charge of the largest environmental cleanup effort in our nation's history, an effort led by Adm. Thad Allen, who has almost 40 years of experience responding to disasters," Obama said.

BP spokesman John Curry said the analysis of the increased oil-flow estimate included data provided by BP.

First oil-flow estimate was 1,000 barrels a day

"We want what everyone wants," he said. "We want to do whatever we can to capture all the oil we can to minimize the impact."

BP is working to contain more of the leak at the sea floor: the Lower Marine Riser Package cap now in place can capture as many as 18,000 barrels of oil per day. A second containment option could expand that capacity to 20,000-28,000 barrels per day, the information center said, and BP said Tuesday its response "is not determined by flow rate estimates."

"Our primary concern is to capture as much oil as possible," BP spokesman Toby Odone told CNN after the new estimates were published. "We are building options to contain higher volumes of oil."

Tuesday's increased oil-flow estimate brought together the work of several scientific teams and was based on a combination of analyses of high-resolution videos, acoustic technologies, and measurements of oil and pressure measurements inside the top hat.

Track the oil spill day by day

"We need to have accurate and scientifically grounded oil flow rate information both for the purposes of the response and recovery and for the final investigation of the failure of the blowout preventer and the resulting spill," Salazar said

Meanwhile, government negotiations with BP are continuing on a BP-funded escrow account to pay for oil-spill damage claims, with a main sticking point being whether workers who lose their jobs due to the government's six-month moratorium on offshore drilling could file for damages, two senior administration officials said Tuesday.

Lawmakers hammered oil companies Tuesday as Obama toured the Florida coast to reassure Americans that the government had firm command over the oil disaster in the Gulf of Mexico.

"This is an unprecedented environmental disaster," he told a crowd of soldiers, Marines and sailors at Pensacola Naval Air Station. "This is an assault in our nation's shore, and we're going to fight back with everything we've got."

Obama meets Wednesday with the chairman of oil giant BP, which owns the broken well at the bottom of the Gulf, and the president made clear he expects BP to pay all clean-up costs and damages from the massive leak.

BP announced Tuesday that it accelerated commercial large-loss claims and has approved 337 checks for $16 million to businesses that have filed claims in excess of $5,000. Initial payments began over the weekend and will be completed this week, the British energy giant said.

In Washington, senior Democrats launched a blistering attack on oil companies at a key House subcommittee hearing.

Congress holds BP's feet to the fire

Rep. Henry Waxman, D-California, said that four of the five largest oil firms have produced disaster response plans that discuss how to protect walruses, even though there are no walruses in the Gulf.

These are "cookie-cutter plans" that, in reality, are little more than "just paper exercises," he said.

Rep. Ed Markey, D-Massachusetts, blasted the heads of ExxonMobil, Chevron, ConocoPhillips, BP, and Shell Oil for producing disaster response plans that are "virtually identical."

Health threats from the Gulf oil disaster could last for years, and officials lack knowledge on how long chemicals in the spilled oil and dispersants will remain toxic, a health expert told a Senate committee Tuesday.

What's the condition of Gulf seafood?

A Food and Drug Administration official told a Senate committee Tuesday that seafood from the Gulf of Mexico available to consumers in stores and restaurants is safe.

"We are confident that Gulf of Mexico seafood that is in the market today is safe to eat," said Mike Taylor, deputy commissioner of the FDA.

Also Tuesday, twice suspended the operation to siphon oil from the ruptured well in the Gulf of Mexico, once after a fire aboard a drill ship, the Deepwater Horizon Unified Command said on its website.

The fire Tuesday morning was likely caused by a lightning strike, and siphoning was suspended as a precaution, BP said. There were no reported injuries.

Later Tuesday a faulty sensor led officials aboard the drill ship Discoverer Enterprise to halt collection of oil from the ruptured well into a containment vessel located a mile below, on the floor of the Gulf of Mexico. Collection resumed after 30 minutes, the command said on its website.

The spill now dwarfs the 11 million gallons that were dumped into Alaska's Prince William Sound in 1989 when the tanker Exxon Valdez ran aground, and oil in varying amounts and consistencies has hit the shores of Louisiana, Mississippi, Alabama and Florida.

BP has been siphoning oil from a containment cap placed on the ruptured well but had to suspend oil collection Tuesday after a fire aboard the drilling ship Discover Enterprise.

iReport: Track the oil disaster. Is the oil spill affecting you?

A statement from the company attributed the fire to lightning. It said operations would restart Tuesday afternoon.

Meanwhile Tuesday, federal authorities announced guidelines to speed up maritime waivers that would allow more foreign ships -- in addition to the 15 already in the Gulf of Mexico -- to assist in oil cleanup efforts.

"Should any waivers be needed, we are prepared to process them as quickly as possible to allow vital spill response activities being undertaken by foreign-flagged vessels to continue without delay," said Allen.



CNN's Dana Bash, Anderson Cooper and Ed Henry contributed to this report.