NYPD Plans to Release Non-Toxic Gases in the Subway

The NYPD will release and track harmless gases in NYC's subway to better prepare for accidents and terrorist attacks
Morning commuters crowding into a New York subway car Photograph by Robert Nickelsberg/Getty Images

In an effort to prepare against chemical, biological and radiological attacks in the New York subway, the New York Police Department has announced plans to release harmless gases into the city’s streets and subway stations to better understand the pathways of airborne contaminants. Officials will use more than 200 sensors, set up throughout all five boroughs, to track these benign gases as they disperse. They’ll then use that data to build a computerized model that can help predict how airborne contaminants might behave, depending on locational and weather conditions.

“If some sort of poison or contaminant were dispersed in the atmosphere of New York City, either accidentally or through a terrorist attack … we’d have an idea how it would travel,” says Paul Browne, deputy commissioner of the NYPD. “That would help guide us as to what our responders should do and what instructions we should give the public—for example, do you shelter in place or do you evacuate—and if so, in which direction.”

The so-called Subway-Surface Air Flow Exchange test is being funded by a $3.4 million Department of Homeland Security Transit Security grant and performed in partnership with the U.S. Department of Energy’s Brookhaven National Laboratory. It will take place in July on three non-consecutive days chosen for variance in weather conditions. The public will receive a day’s notice.

The gases, known as perfluorocarbon tracer gases (PFTs), are colorless, odorless, and non-toxic, and they will be released at very low levels. “We’re talking grams of material dispersed over about a half-hour,” says Paul Kalb, division head for environmental research and technology at Brookhaven. “You won’t see anything or detect anything.”

PFTs have been used since the 1980s to learn about airflow in cities, including Washington, Boston, and New York’s Manhattan. Tracer gases are also used to track air pollutants such as coal fire soot, find air leakages in buildings, and even track kidnapping ransom money (PDF).

New York already has several airborne contaminant detection mechanisms in place, although they don’t track the movement of air: Police officers wear radiation detection devices on their belts, and police stations and some subway stations are outfitted with air analysis devices that get checked every 24 hours to see if they’ve collected biological or chemical contaminants, says Browne.

The NYC study will be by far the largest urban airflow study to date, according to Brookhaven. Seven different PFTs will be released at seven locations and then tracked by air samplers set up on street lamp posts and in dozens of stations along 21 subway lines. But don’t expect to learn the results of the study: “That information [about how the air travels], by the way, is not going to be made public,” says Kalb. “The city wants to make sure they’re not helping terrorists do their deed.”

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