Federal officials backed away yesterday from a plan to fumigate a Senate office building with chlorine dioxide gas to kill anthrax spores after outside experts raised questions about the decontamination technique.
Instead, workers will clean the Hart Senate Office Building piecemeal using various disinfectants, including bleach and bacteria-killing foam as well as the gas.
It was unclear whether the new approach would still allow 50 senators to return to their offices by Nov. 13, the goal under the previous plan. They were forced to abandon the building three weeks ago, after a tainted letter to Senate Majority Leader Tom Daschle of South Dakota exposed 28 staff members to anthrax.
As the cleanup plan was revised, investigators from the federal Centers for Disease Control and Prevention in Atlanta were studying whether some people might be particularly susceptible to inhalation anthrax. Investigators still had not figured out how a New York hospital worker who died of the disease and was buried yesterday became infected with anthrax.
A Pentagon post office became the latest facility to close after traces of anthrax were found there Sunday, and postal inspectors prepared to search tons of decontaminated mail for clues to the attacks.
The change of plans for the Hart building came after outside experts from a dozen institutions offered written comments on the Environmental Protection Agency's decontamination plan.
The comments were not made public yesterday, but one University of Texas expert said he had warned the EPA that chlorine dioxide gas could damage computers and other electronic equipment.
"I think they underestimated the damage chlorine dioxide could do," said Lee H. Thompson, safety director for biological containment facilities at the University of Texas Medical Branch in Galveston. "It's quite corrosive to copper and other metals."
Noting that most buildings that have been decontaminated were laboratories, Thompson said a huge office building with irreplaceable paper files and valuable furnishings poses a far greater challenge.
"They've got a hell of a project ahead," Thompson said.
EPA spokeswoman Bonnie Piper said comments on the fumigation plan were solicited from military research centers, academic specialists and private corporations. Most experts thought chlorine dioxide gas would kill anthrax, she said.
"The unknown was, 'How do you use it on a building that big?'" Piper said. The decision was made to clean the building in phases, using various techniques.
Lt. Dan Nichols of the Capitol Police said cleaning will begin immediately in a stairwell and freight elevator in the Hart building, using a decontamination foam developed at Sandia National Laboratories.
In other parts of the building, cleanup workers will use special vacuum cleaners to filter out microscopic spores and kill them with bleach, Piper said.
The EPA announced its fumigation plan Oct. 29 after consulting with industry experts. But the agency said it would seek outside comment before sealing the Senate office building and filling it with chlorine dioxide gas.
In the U.S. biological weapons program, which was closed in 1969, buildings were decontaminated using formaldehyde gas. But the caustic formaldehyde cannot be removed completely from porous substances such as paper and carpet, making that method impractical for the Hart building, Thompson said.
As the EPA struggled over cleanup methods, CDC epidemiologists hunted for patterns among the anthrax victims. To date, 17 cases of anthrax have been confirmed, including 10 of the dangerous inhalation form of the disease. Four people have died.
Researchers are gathering data to see if they can determine whether advanced age or a history of smoking might make people more vulnerable to inhalation anthrax, said Dr. Bradley Perkins of the CDC.
The 10 inhalation anthrax victims range in age from 43 to 73, with a median age of 56, or 21 years above the median age in the United States. And, while only one was a smoker when infected, Perkins said, several are former smokers.
Medical detectives still have not been able to figure out how 61-year-old hospital worker Kathy T. Nguyen was infected, Perkins said. Funeral services were held yesterday for Nguyen, a Vietnamese immigrant.
Environmental tests found no anthrax in her Bronx apartment building, at the Manhattan hospital where she worked, along her subway route, or in a restaurant where she ate and sometimes worked, Perkins said.
Even her clothing - initially reported to have tested positive for anthrax - proved negative in more definitive tests.
As Nguyen was buried, a 56-year-old New Jersey postal worker became the third survivor of inhalation anthrax to recover sufficiently to leave the hospital.
Norma Wallace, 56, of Willingboro, worked as a mail handler at the Hamilton facility that is believed to have directed three anthrax-tainted letters. She believes that she contracted the disease Oct. 9 when a co-worker shot compressed air into a jammed mail-processing machine and sent dust flying.
Her employer, the U.S. Postal Service, said tests have been completed on 102 of the 260 postal installations scheduled for examination. So far, 60 facilities have received a clean bill of health and 14 have tested positive for anthrax, said Azeezaly S. Jaffer, vice president for communications.
A retail post office inside the Pentagon closed Sunday after environmental tests found "slight traces" of anthrax in two rental mailboxes. No illnesses have been traced to the site.
Jaffer said postal authorities continue to divert mail addressed to U.S. government offices in Washington, trucking it to Lima, Ohio, for irradiation to kill any anthrax spores.
The mail is then returned to Washington, where postal inspectors will search for more anthrax-laced letters that could offer clues for the investigation, Jaffer said.
Wire services contributed to this article.