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Questions and Answers

What is S-SAFE?

The Subway-Surface Air Flow Exchange (S-SAFE) is a project designed to study air flow in the dense, complex urban environment of New York City, both below- and above-ground. The New York City Police Department and the U.S. Department of Energy's Brookhaven National Laboratory are conducting the study to better understand the risks posed by airborne contaminants, including chemical, biological and radiological weapons if they were to be dispersed in the atmosphere and in the City's subway system.

How will the public benefit from this study?

Air flow and thus the dispersion of airborne hazards in New York City cannot be easily predicted due to the City’s highly urban environment with tall buildings, street canyons and a large and complex subway system with rail tunnels relatively close to the street level.  Effective planning for emergency response to the airborne hazards, including chemical, biological and radiological agents, requires better understanding of the air flow currents and potential dispersion pathways and phenomena unique to the New York City environment.

In the event of emergency involving dangerous airborne material, NYPD and other first responders will be better informed and prepared to protect, or evacuate if necessary, the public, including subway commuters.  In addition, New York City agencies will have site-specific air flow data to refine their emergency response.

How will the study be conducted?

On the morning of each test day, researchers will disperse small amounts (measured in parts per million) of several different perfluorocarbon tracers (PFTs) from several locations in the subway and at street level. Approximately 200 state-of-the-art air samplers will be deployed throughout the five boroughs to track the movement of the tracers. The concentration of the tracers will be very minute (measured in parts per billion or less). At the end of each day’s study period, the contents of the samplers will be collected for analysis.

When will these tests be conducted?

Testing will occur over three non-consecutive days between July 8 and July 28. Selection of test days is weather-dependent, so the decision to proceed will be made the day before the test and announced on the S-SAFE website, through social media channels and provided to the news media.

Are perfluorocarbon tracer gases safe?

Yes. The S-SAFE study will use very small amounts of PFTs at very low concentrations. These tracers are colorless, odorless, biologically inert, non-toxic and non-combustible gases. Perfluorocarbon compounds can be inhaled or ingested with no concern and are nontoxic even at high concentrations.

Who is paying for this study?

The S-SAFE field study is funded by the NYPD through a $3.4 million Department of Homeland Security Transit Security Grant.

Where can I get more information?

For more information, visit the S-SAFE website home page.