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."