The assessment was given to the Senators during a closed meeting by Tennessee Senator Bill Frist, reports CBS News Chief Washington Correspondent Bob Schieffer. Frist is also a doctor and has been working on the situation here with health officials.
Meanwhile, officials have decided to pump chlorine dioxide gas into the shuttered Hart Building to rid it of potentially deadly anthrax spores, Daschle said Tuesday.
Pending a final approval by scientists who are studying the plan, Daschle said the process should allow the building to reopen around mid-November. Half the Senate's 100 members have their offices in the building, which has been closed since Oct. 17, two days after Daschle's office received an anthrax-laden letter.
That letter released two grams of anthrax containing "billions of spores" of the bacteria, Rep. Mike Pence, R-Ind., told reporters Tuesday. Scientists have said it takes 8,000 to 10,000 spores to make someone ill with the disease.
Pence, who has met with health officials and investigators, is one of three lawmakers whose offices in the Longworth House Office Building have been found to have anthrax traces. In a conference call with reporters, he said the amount of anthrax in Longworth is infinitesimal compared to the amount in Daschle's office.
Environmental Protection Agency officials are hoping that experts would approve using chlorine dioxide in the nine-story Hart building in the next day or two. Once they do, the building will be sealed off and EPA will start the process, expected to last 16 days.
"We're going to go ahead with the process EPA recommended," Daschle, D-S.D., told reporters.
As a precaution, the adjacent Dirksen Senate Office Building will be closed for two days while the Hart building is flushed with gas, senators were told Tuesday. The two buildings are connected by passageways in their staircases and basement.
Twenty-eight people in or near Daschle's office were exposed to the potentially deadly bacteria, and 6,000 others on Capitol Hill were tested for exposure. All six of Congress' major office buildings and the House side of the Capitol were closed.
Chlorine dioxide, which is used to purify water in many American and European communities, has not been used to kill anthrax in the field before, officials said. But it has been successful against bacteria that are considered even harder to destroy, said Paul Schaudies, a microbiologist and a consultant to the EPA.
The gas should punch holes in the hard coating around the anthrax spores and destroy its genetic matter, he said.
"It'll take that spore that's now a hard ball and make a whiffle ball out of it," Schaudies said.
After the gas is pumped into the building, it would not be reopened until teams ensure that anthrax spores have been killed, said senators and EPA officials.
Lawmakers said they did not know how much the cleanup would cost.
Meanwhile, trace amounts of anthrax were found in a Capitol Police office in the Ford House Office Building, said a congressional official speaking on condition of anonymity. Officials think the anthrax may have been tracked in by officers who went to Daschle's office the day the letter was received.
The Ford building, which houses the Congressional Budget Office but no lawmakers' offices, remains closed. Anthrax had already been found on a mail sorting machine in that building.
The Longworth House office building probably will not reopen until at least next week as testing for anthrax there continues, aides to lawmakers with offices in that building were told Monday.
Over the weekend, anthrax traces were found in the 6th and 7th floor offices of three representatives. No additional anthrax has been found since then, officials said.
"Until every single test is documented and confirmed, we simply won't open that building up," said Rep. Bob Ney, R-Ohio, chairman of the House Administration Committee.
The Hart and Longworth buildings are the buildings with lawmakers' offices that have not reopened.
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