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Chemical detection sensors at the new World Trade Center Transportation Hub

Although nearly all countries in the world have signed a Chemical Weapons Convention treaty for prohibiting the production and usage of chemical warfare agents, “there is a concern that people can secretly make these types of deadly chemicals, and easily walk in the subway with a backpack and release them,” said Bansleben. “To save lives, the Port Authority is interested in protecting this very large space.”

The Oculus is not the first place to be equipped with chemical sensors. U.S. public transportation spaces such as the Grand Central Terminal in New York City, and Washington, DC metro system have used such devices since the early 2000s. Hidden in nonobtrusive vented cabinets, chemical detectors are constantly sampling and scanning the air, looking for hazardous gases.

S&T, which funds this project, contracted the Argonne National Laboratory to install chemical sensing technology in a fashion to achieve maximum coverage of the volume of the Oculus. To achieve more reliable detection, the Lab will install different types of sensors that use two different physical techniques—point and standoff. If both techniques independently confirm a dangerous chemical present in the area, authorities will be alerted that a hazard is present.

Point detectors register only substances that are close to them. These detectors sample the air to look for hazardous gases using Ion Mobility Spectroscopy and compare them quickly to a library of chemicals.

Standoff detectors cover large areas via an infrared laser using the analytical technique of Fourier Transform Infrared Spectroscopy. 

“For example, one of these sensors may be sending an infrared beam across a large space, and if the beam passes through a cloud of hazardous material, it may absorb the energy,” said Bansleben. “Every molecule has a fingerprint in the infrared region and will absorb energies at different frequencies; if there is a match, security would be alerted.”

Sometimes cleaning chemicals may cause an alarm to go off because of a similarity in a physical property to a threat chemical. False alarms, if they were to occur often, are problematic because they may cause unnecessary evacuation and thus make the technology unreliable. “Combining multiple

techniques is the best way to achieve protection and avoid false positives,” Bansleben said.

If a sensor at a certain location identifies a hazard, it will alert the local operations center. Then the operators will notify security and, if needed, the Fire Department, First Responders, and the Police. If the authorities predict a wide spread of the chemical, they will evacuate the public immediately.

S&T notes that the project started just after September 11 this year, and the detectors, which will not be in plain sight, will be tested in the Oculus for a period of 12 months under S&T’s guidance. This period allows the Argonne National Lab to see how accurately the devices work, analyze collected data, and work with detector vendors to improve the technology.

After a year of successful testing, the Argonne National Lab will teach the Port Authority how to use the chemical detectors for another year. Then in 2019, S&T anticipates donating most of the detectors to the Port Authority so that it integrates them into its emergency response actions.

“The World Trade Center is something that has a lot of meaning for this country since 9/11,” said Bansleben. “We are proud to support and protect public transit systems from terrorism.”