The MTA and the Department of Homeland Security announce new tests to prepare for the unthinkable: the possibility, however remote, of terrorists releasing a deadly gas in the subway. NY1's Vivian Lee got a sneak peek.

It's no bigger than a toaster oven, but officials say it will help protect New Yorkers from a terrorist attack in the subways.

"This will tell us real-time data on aerosol concentrations, or the particle concentrations," Dr. David Brown of the Argon National Labs said as he held up one of the protective machines.

Roughly 200 machines, like the one seen in the video above, are planned to filter the air in more than 50 subway stations in Manhattan, Brooklyn, and Queens next week.

They'll be looking for tracer particles and gas that will be released at Penn Station, Times Square, and Grand Central Terminal.

"The particles we release will have a florescent — a very small amount of fluorescent material," Brown said. "So, it can pick up that fluorescent material and discriminate that against all the other particles that are in the subway."

The data will help the MTA and scientists with the Department of Homeland Security learn how air travels underground, in the event of a biological or chemical attack.

"On what surfaces does it deposit?" said Dr. Donald Bansleben of the department's Science and Technology wing. "Where does it deposit in trains? Where does it deposit on clothing of people that may be actually in the subway at that time?"

The gas and particles being used for the study are not harmful, but the findings could be crucial in the event of a real attack.

In 1995, sarin gas released by a doomsday cult in the Tokyo subway system killed 13 and injured more than a thousand. Air underground moves because trains do.

"The primary mover is the movement of those trains," Dr. Charles Burrus of the MTA said. "If we have information early that there a contaminant in a particular station or location, and we suspend the traffic in that area, we retard the movement of that contaminant."

"We are living in a society where there are chemicals in the air and possible attacks by terrorists," one subway rider said. "I think it's definitely beneficial they do whatever they have to do to get the job done and keep us safe."

The study takes place Monday, May 9 through Friday, May 13.

Officials say at those times there is no known credible threat against the transit system in the city.