Rande,
Experts Say Spores Won't Spread in Ventilation System [NYT]
nytimes.com
October 18, 2001
THE STRUCTURES
By JAMES GLANZ and DAVID E. ROSENBAUM
Experts on biological warfare and building design said yesterday that it was extremely unlikely that the anthrax spores mailed to Senator Tom Daschle could have been spread in dangerous amounts to the rest of the Hart Senate Office Building through the ventilation system.
Even what were apparently finely ground, weapons-grade spores containing anthrax would be quickly diluted in any ordinary office building and at least partly filtered by a standard office ventilation system, as long as it was up to current standards, the experts said. And once contaminated air left the building through its exhaust pipes, the concentrations of the spores would be far too low to cause infection.
"Once it goes to the outside, it'll quickly be diluted so that it's not a hazard," said Richard Spertzel, a former weapons inspector and senior biologist for the United Nations Special Commission on Iraq.
Government investigators quickly shut down the Hart Building's ventilation system to eliminate any chance that the disease could be spread farther, and Mr. Spertzel said they acted properly. But he added that weapons-grade anthrax, which wafts in the air and seldom sticks to surfaces, would have been cleared from the area by the ventilation system, often called H.V.A.C. for heating, ventilation and air conditioning.
"If you left the H.V.A.C. on," he said, "you could walk in there in two to two and a half hours and be perfectly safe."
Still, the experts said the incident would bring attention to recommendations that have long been put forward to reduce the damage that bioterror attacks — whether from outside a building or, as in this case, inside — are likely to cause.
Those recommendations include keeping the air pressure in office buildings at a slightly higher pressure than the outdoors, carefully monitoring all intake vents and adding high-efficiency filters to all heating and air conditioning systems. For anyone who is particularly worried about the threat, mobile filters, available commercially, will more quickly cleanse the air in individual offices.
But even without those measures, the likelihood of mass exposures through air circulation within a building is minute, said James E. Woods, founding director of the HP- Woods Research Institute in Herndon, Va.
"There's a huge fear factor, but when we stop and think about it, the probability of getting exposed is pretty low," said Mr. Woods, who is also chairman of the environmental health committee of the American Society of Heating, Refrigerating and Air Conditioning Engineers, which sets standards for the field.
The nine-story Hart Building is built in the shape of a cross as seen from above; inside, at the center of the cross, is a dramatic 100-foot atrium. The building houses the offices of about 50 senators and is connected through open corridors to the Dirksen Building, which also contains Senate offices.
The letter to Mr. Daschle, the Senate majority leader, was opened in his office, in the building's southeast quadrant. That quadrant has now been closed off. Government officials said its ventilation system was not connected to the rest of the building.
"Those ventilation systems have been off since shortly after the letter was opened, to minimize any further spread," said Robert Gibbs, program manager of the Defense Advanced Research Projects Agency, at a news conference with Senator Daschle and others this afternoon.
To become infected with inhalational anthrax, the deadliest form of the disease, a person would have to inhale 8,000 to 10,000 spores no larger than about five microns. The filters in the systems of newer office buildings should remove about 90 percent of particles of that size in a single pass, said Mr. Woods, of the heating engineers' society.
More advanced filters, called HEPA for high-efficiency particulate air filter, take out at least 99.97 percent of such particles in a single pass, Mr. Woods said. But those filters are often 5 to 10 times as expensive and require more powerful air- circulation systems, and so are not used in many buildings. Officials refused to comment on the ventilation systems used in federal buildings in Washington.
Experts cautioned that a ventilation system could be used to spread lethal quantities of anthrax. An attack with the potential to cause much larger numbers of casualties would involve infusing huge amounts of anthrax into one of the building's intake vents. The best solution, Mr. Spertzel said, is to "guard it so nobody has access to it."
About the possibility that anthrax or some other biological weapon could be released into the outside air, Dr. Richard L. Garwin, a physicist who is an authority on weaponry at the Council on Foreign Relations in New York, suggested a way to protect people who stay inside: use the ventilation system to keep the building's air pressure slightly higher than that of the surroundings, so that contaminants do not enter through windows and doors.
There are even measures for reducing the threat of a bioweapon already inside a building.
Dr. Thomas J. Johnson, director of the division of respiratory care on the Brooklyn campus of Long Island University, said emergency rooms had long taken measures to protect against small, lethal particles — in their case, drug-resistant tuberculosis bacteria on the droplets released when patients cough.
The emergency rooms use mobile HEPA filters with their own fans, he said. Another bioweapons expert, Dr. Matthew S. Meselson, said that such units sell commercially and that he keeps one in his office at Harvard, where he is a professor of biology.
Both Dr. Johnson and Dr. Meselson said that those filters could not eliminate the danger of anthrax infection in a contaminated building, and that the best defense was to stop the attacks from occurring in the first place. But they said the filters showed that other protections were available.
"We know we can do some good, basic protection of individuals using the same methodology we used for multidrug-resistant TB," Dr. Johnson said.
Fred |
