If you see something next week, think twice before you say something

Homeland Security researchers will be back underground next week, spraying inert gases and taking readings at 20 T stops and aboard subway trains, as part of their efforts to figure out the best way to counter any biological or chemical attacks on mass transit.

Particle and gas concentrations will be sampled in more than 20 stations and in subway cars covering the entirety of the underground portion of the MBTA subway system. While the deliberate release of chemical or biological agents is of primary concern, the study will also help researchers understand airflow characteristics for smoke or unintentional spills of chemicals or fuels—providing a direct benefit to MBTA for use in developing evacuation, ventilation, and other incident response strategies. The information will also help guide the design of next generation chemical and biological agent detection systems.

Although the equipment will be visible, the study will not disrupt normal activities or present any inconvenience to the public. Commuters may notice a variety of electronic equipment positioned in stations or being hand-carried by researchers.

The researchers did similar studies here last December; they want to do it again to take into account the differences between winter and summer conditions. Homeland Security adds:

The tests will use sulfur hexafluoride and perfluorocarbon gas tracers, both innocuous, non-toxic, inert gases that have been used in dispersion experiments since the 1960s. Sulfur hexafluoride is a harmless, common tracer gas used for indoor and outdoor air testing. Perfluorocarbons are used in eye surgery and other medical applications. An inert particle tracer will also be used. These tracers are tagged with sodium fluorescein and a common optical brightener. Sodium fluorescein is a biologically inert, non-toxic organic dye used in oceanography as a marker in seawater, and in medical imaging applications. The optical brightener is used in many laundry detergents and in paper manufacturing.