A Senate office building contaminated in several areas by anthrax mailed to Senate Majority Leader Tom Daschle may remain closed until mid-November after it is fumigated with a chlorine-based gas, U.S. officials said on Monday. 
The Environmental Protection Agency plans to use chlorine dioxide gas to decontaminate the Hart office building, which was closed on Oct. 17, after a letter containing anthrax spores was opened in Daschle's office two days earlier. 
Twenty-eight people, most of them staffers to the South Dakota Democrat, tested positive for exposure to the potentially deadly spores. They have been treated with antibiotics and none has become ill. 
EPA officials and Assistant Senate Majority leader Harry Reid said at a briefing for reporters the fumigation procedure will take 16 days. If it goes according to schedule, the building would be reopened on Nov. 13. 
The plan to use the type of gas not used on anthrax before was to be reviewed by experts in the EPA and other agencies a final time later on Monday and on Tuesday, the officials said. The gas has successfully destroyed other bacteria considered tougher than the anthrax strain, they said. 
EPA officials assured senators that the plan was "the quickest, most protective and least disruptive approach we can take," said Reid, a Nevada Democrat. 
He also said lawmakers were told it was the only way to safeguard papers, art work and other valuable artifacts in their offices. 
EPA officials said they would seal off the office building, which is joined by a basement hallway system to other Senate buildings and the Capitol. 
They said the gas breaks down quickly, and they have a set of procedures to verify the destruction of the anthrax spores. 
After an earlier closed briefing with EPA officials, Sen. Larry Craig, an Idaho Republican, said full fumigation of the building was needed because there was contamination on several floors and on an air vent. 
Foams and other types of applications that could have been used more quickly on surfaces and without fully closing the building could not be used "without risking the spores to go airborne," Craig said. 
Since the building was closed, many senators have had to set up makeshift offices, with their staffs scattered in spare rooms in other buildings. 
"You've got 50 senators, myself among them, working in nooks and crannies of the Capitol," said Sen. Byron Dorgan, a North Dakota Democrat. But he said it was worth it to ensure that the building is safe. 
"What every senator wants is the building to be safe for their staff," Craig said. 
Asked about the cost of the fumigation, Reid said, that was not considered. "It will cost whatever it takes to make the building safe," he said. 
In addition to the area around Daschle's office on the fifth and sixth floors of the Hart Building, spores have been found in an air conditioning filter on the ninth floor, at the stairwell leading from the eighth to the ninth floor, and at a first floor elevator bank, officials have said. 
Small amounts of anthrax also have been found in three other Capitol Hill office buildings.