In 1995, the subway system in Tokyo was the target of a domestic terrorism attack involving a potent gas called sarin, a chemical weapon that can cause neurological damage and even death. In five coordinated incidents, members of a radical-religious group known as Aum Shinrikyo released the sarin gas on five trains in the Tokyo subway system. The attack killed 12 commuters, seriously injured 54 and affected 980 more who experienced some health effect. The lesson learned in the tragedy was that chemical agents have the potential do widespread damage -- and a subway system provides an ideal environment for dangerous gas to travel fast.
See pictures from the DHS test in our slideshow: Images from a homeland security experiment
A terrorist attack on a U.S. subway system using biological agents is an ongoing concern for the U.S. Department of Homeland Security. Chemical weapons, particularly airborne contaminants, are usually invisible and not easily detected until after they have been released and have caused significant damage. As part of an effort to enhance emergency response and security in the country's transportation systems, DHS officials have been conducting a scientific study of airflow throughout the underground portion of the subway in both Boston and Washington.
While Washington D.C. has the newest subway system in America, Boston's MBTA subway system is the oldest of its kind in the country (Related: MBTA flaw disclosure: The students speak up). Inside the "T," as it is known to locals, a scientific team placed equipment - electronic monitoring devices used to gather data on the behavior of airborne contaminants if they were to be released into the subway. The research was conducted in two stages; the first portion was conducted in December 2009, the second in August 2010.
"The movement of airborne contaminants can be affected by differences in temperature and humidity, so a comprehensive study requires gathering data in both winter and summer months," said program manager Teresa Lustig. "In addition to comparing the effects of seasonal conditions, a second phase of the study also allows us to test the effectiveness of some of the proposed countermeasure and response strategies derived from analysis of the December tests."
CSO recently observed the team preparing for the second phase test in Boston. To collect data on the behavior of airborne contaminants, the scientists released two types of innocuous tracer gases; sulfur hexafluoride and perfluoro-carbon. Both are stable, colorless, odorless, non-combustible gases that have been used extensively and safely as atmospheric tracers since the 1960s. The tracer gases cause no health risk or damage to materials and were released at low concentrations, according to DHS officials. However, the materials move like any chemical agent, and can give scientists a sampling of just how quickly an airborne contaminant can travel in a subway.
"Once an aerosol is released into the air, it takes awhile for it to settle," explained researcher David Silcott, general manager of IBX Biodefense."Once a train comes along, it pushes it down further into the system."
Particle and gas concentrations were sampled in more than 20 stations and in subway cars covering the entire of underground portion of the MBTA subway system. Boston's T, in contrast to the newer and streamlined equipment of Washington, D.C.'s subway, was built over a long period of time in several stages, which is one reason it was selected for the testing.
"Because the Boston system was built over time, the train cars are different for each line," said Lustig.
The results will help MBTA authorities develop a plan to quickly detect an attack and shut down subways to limit the spread of contaminants. While the test is primarily to gauge behavior of chemical or biological agents, the study will also help researchers understand airflow characteristics for smoke or unintentional spills of chemicals or fuels, said Lustig. The results can help MBTA officials develop evacuation, ventilation, and other incident response strategies, too, she said.
By looking at the data we collect from the two vastly different systems, we can apply what we learn to other subways systems across the nation and to our international partners--all in the effort to keep travelers safe."
This story, "DHS simulates terror attack in subway systems" was originally published by CSO.