Commuters in Boston's MBTA subway system will notice scientific equipment and researchers with electronic monitoring devices throughout the system August 20 -27, while the U.S. Department of Homeland Security (DHS) continues a scientific study of airflow throughout the underground portion of the subway system. The first portion of the study was conducted in December.

Led by DHS's Science and Technology Directorate, the purpose of the study is to gather data on the behavior of airborne contaminants if they were to be released into the subway-part of the Department's ongoing commitment to preparedness and the shared responsibility of protecting the nation's critical infrastructure.

"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."

"Our customers and employees should know that the MBTA is working closely with our federal partners in order to make the transit system as safe as possible," MBTA Transit Police Chief Paul MacMillan added.

In order to collect data on the behavior of airborne contaminants, the study involves releasing non-toxic, inert, odorless gas and particle tracers into the subway system. 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 study will be conducted by researchers from Argonne National Laboratory, Lawrence Berkeley National Laboratory and an international team from ICx Technologies of Arlington, Va., Defence Science and Technology Laboratory of the United Kingdom and Chemistry Centre of Australia.

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.