Metro Set To Initiate Chemical Sensors
washingtonpost.com
Use at 2 D.C. Stations A First for Subways
By Lyndsey Layton
Washington Post Staff Writer
Tuesday, December 25, 2001; Page A01
After two years of experimenting in secret, Metro will activate sensors in two downtown stations next month and become the first subway in the world that can detect a release of toxic chemicals.
The move signals that the technology is ready for use in other subway systems, airports, shopping malls and other large, enclosed public spaces, federal scientists say.
Anthony Policastro, an engineer at Sandia National Laboratory who is overseeing the Metro project, said his team will continue to improve the sensors but that the basic system works. "We have been testing for some time, and we're satisfied," he said.
That has encouraged subway managers in Chicago, Atlanta and Los Angeles, who, along with National Park Service officials, have expressed interest in the technology, Policastro said. Boston has begun experimenting with a sensor at the suggestion of the Massachusetts Institute of Technology's Lincoln Laboratory, which is providing technical expertise to the subway. The Park Service is considering installing sensors in the Statue of Liberty.
And scientists are installing sensors in an undisclosed airport, Policastro said.
Work on the $7.5 million Metro sensors began in 1999 and was progressing quietly until Sept. 11, when the terrorist attacks made it a priority among lawmakers and administration officials. On Thursday, Congress approved $15 million to expand Metro's sensor program from two stations to 12. Transit Police Chief Barry McDevitt said that the goal is to install sensors in all 47 underground subway stations.
Although chemical sensors have been available to the military for some time, use in public spaces, such as shopping malls and subway stations, is new.
Until now, the only way to analyze the air in those places has been to sample it and take it to a laboratory, a time-consuming task. A sensor is like "a chemical technician in a box" that can automatically alert authorities, said Jonathan Kiell, a spokesman for the Department of Energy's National Nuclear Security Administration.
The sensors are similar to fire alarms in a home, Kiell said. An alarm is key during a chemical release because a quick evacuation can save lives.
One challenge faced by scientists working on the Metro project has been getting the sensors to distinguish toxic chemicals from a host of background chemicals found in the air in subway stations.
The sensors, which are about the size of a shoe box and are hidden in the two stations, continuously suck in air and analyze it. When they detect one of several toxic chemicals, they bleat quietly and sound an alarm in Metro's operations control center. Policastro won't discuss the chemicals the sensors are designed to detect. Metro asked The Washington Post not to identify the two stations.
The devices are not yet able to pick up biological agents, such as anthrax and smallpox. The military has sensors that can detect biological agents, but they are bulky and expensive and have been troubled by false warnings. Policastro said it will be a couple of years before one is developed for use in the subway.
But the Metro program, known as Protect, is about more than sensors.
To understand how a toxic chemical might spread in a subway system, federal scientists studied the way air moves through the Metro and how trains complicate that movement.
They found that a chemical that is released inside a train travels with the speed of that train, spreading a toxic plume as the train moves.
"We call it an unwanted passenger," said Policastro, who released smoke into the subway system in the middle of the night and tracked its trip through the system. "It moves along, station by station."
A chemical released on a station platform can spread to adjoining stations when trains are running because rail cars act as pistons, pushing and pulling air through subway tunnels. The piston effect is especially strong in older stations with flat ceilings, such as those in Boston and New York. Washington's coffered ceilings tend to weaken the piston effect, Policastro said.
The fact that trains can disperse chemicals makes subways potential targets for terrorism. The 1995 sarin gas attack in the Tokyo subway killed a dozen people and sickened 5,700.
One contaminated train ran through the system three times before it was stopped.
In 1998, 40 percent of terrorist attacks worldwide targeted transportation systems, with a growing number against bus and rail systems, Federal Transit Administrator Jennifer Dorn told Congress in October.
Added Trixie Johnson, research director at the Mineta Transportation Institute in California: "Terrorists view passenger rail systems as killing fields."
Containing a chemical attack in a subway is complicated by natural flow -- wind that exists in subways even when no train is moving. The Metro system has a natural flow of 1 to 2 mph, Policastro said.
Natural flow makes it nearly impossible to isolate a chemical release in one station and keep it from spreading.
"If there's a chemical release and we shut the trains down to evacuate the people, it doesn't mean the plume is just going to stay sitting there," Policastro said. "It's going to spread to neighboring stations. It's kind of a race between us getting people to safety before that natural current brings the chemical to them."
To understand how air movement affects a chemical release in the subway, meteorologists have mapped how the air flows through Metro's particular stations and developed computer models that predict the way a chemical plume would move, depending on its concentration and where it was released.
The models are used to create a real-time map of a "hot zone" -- the area of the chemical plume -- that can be used by rescue officials to make decisions about evacuations and response efforts. The data can also help transit managers decide whether to turn on ventilation fans and flush the chemicals outside or try to contain the plume inside the station.
"The responders want to know where the danger zone is and how it's going to move over time," Policastro said.
Each of the nation's 14 subway systems has unique characteristics that have to be mapped and modeled so their sensor system will work properly, Policastro said. "Other subway systems could take the system that we have now and install it, but every one needs to be tailored to their particular needs," he said. "You can't take a bunch of detectors and slap them someplace and know what to do."
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