NYPD to Spew (Non-Toxic) Gas in Subway System

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An air sampler on West 47th Street -- part of a scientific study to understand how the subway system affects airflow

To know how to react to a dirty bomb or airborne attack, the New York Police Department simulated one in the subway Tuesday morning. The NYPD and researchers from Brookhaven National Laboratory released a nontoxic gas through 21 subway lines as part of a plan to monitor air flows and chart potential responses, including evacuation routes and where to place emergency equipment.  

"It's planning for the worst and hoping we don't ever have to use it," said NYPD Deputy Commissioner Paul Browne. "When you are able to map a hazardous material in the air, it gives first responders information they need."

Low concentrations of the tracer gas perfluorocarbons were released at several dozen subway stations and at street level in Manhattan at 8:00 a.m, according to Browne. "This study helps us map and predict where those dangerous contaminants would go," he said. "And it's not just terrorism -- it could be accidental, a toxic material accidentally discharged into the environment."

The study was commissioned by the NYPD and funded with a $3.4 million grant from the Department of Homeland Security. It's the largest urban airflow study to date and the first of its scale to track airflow in a dense, complex urban environment both below and above-ground.

And it will help parse how air flows in one of New York's microclimates -- the subway system.

"The subways in New York are somewhat unique because they’re very shallow," said Paul Kalb, a research engineer at Brookhaven and one of the study's principal investigators. "If you walk down the streets, you see grates that are the interchange where air flows into the subway. So if there's a release in the subway, some of that material could come out through the station. Some of that material could be pushed through the tunnel."

Paul Kalb, standing in front of an air sampling box attached to a light pole on West 47th Street. (Kate Hinds)

Air particles even ride the subway, exiting and entering trains as doors open in the stations.

To track the perfluorocarbons, scientists are putting up hundreds of air samplers -- plastic toolbox-like containers attached to light poles and places in the subway system. They will installed before each test and removed several hours later, where they'll be taken to the lab.

"Our detection limits are so good that we can see really minute quantities, "said Kalb. "So a small, tiny tiny amount may go from Times Square to Bronx...and we’ll be able to see that. We’ll also be able to see what concentrations are moving at what rate."

And how far the perfluorocarbons go -- and what quantity they travel in -- is key.

The data from this study will be distilled into a computer program for the NYPD. "So if something happened," said Kalb, "if there were an accidental or a terrorist release of a material, they can say 'okay, here's the location, here's the given wind speed'...and basically push a button and it will tell them 'based on all the information we know, here's what you can expect, and the plume is probably going to head in this direction and therefore you probably want to set up an evacuation zone somewhere else...you may want to take that information and see which subway lines are impacted, which ones have to be closed down, which ones are safe."

Testing for the Subway-Surface Air Flow Exchange program (S-Safe) will occur over a total of three days this summer. The other two days have yet to be announced.

What won't be announced: the results. The data is "for official use only," said Kalb. "We don't want to give potential terrorists a recipe for how to most effectively spread materials throughout the city."