New York Police Commissioner Ray Kelly

New York Police Commissioner Ray Kelly Credit: New York Police Commissioner Ray Kelly (Getty)

The NYPD will again pump a harmless gas through the city's transit system Friday to test the risk of a terrorist attack or accident that spreads dangerous contaminants underground.

Starting at 8 a.m., researchers will disperse the odorless gas for 30 minutes in select Manhattan subway stations. Air sampling, with equipment stationed throughout the city, will last until 3 p.m.

This is the NYPD's second test, after the one on July 9. The project, commissioned by the NYPD, is funded through a $3.4 million grant from the Department of Homeland Security.

The NewsdayTV team looks at the most wonderful time of the year and the traditions that make it special on LI.  Credit: Newsday

'Tis the season for the NewsdayTV Holiday Show! The NewsdayTV team looks at the most wonderful time of the year and the traditions that make it special on LI.

The NewsdayTV team looks at the most wonderful time of the year and the traditions that make it special on LI.  Credit: Newsday

'Tis the season for the NewsdayTV Holiday Show! The NewsdayTV team looks at the most wonderful time of the year and the traditions that make it special on LI.

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