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.

From celebrating America's 250th birthday to a new ride at Adventureland, NewsdayTV's Elisa DiStefano and Newsday lifestyle editor Meghan Giannotta have your inside look at Newsday's summer FunBook. Credit: Newsday/Howard Schnapp, Kendall Rodriguez, Drew Singh; Anthony Florio, Randee Daddona, Morgan Campbell, Debbie Egan-Chin

Get ready for sun and fun with NewsdayTV's summer FunBook special! From celebrating America's 250th birthday to a new ride at Adventureland, NewsdayTV's Elisa DiStefano and Newsday lifestyle editor Meghan Giannotta have your inside look at Newsday's summer FunBook.

From celebrating America's 250th birthday to a new ride at Adventureland, NewsdayTV's Elisa DiStefano and Newsday lifestyle editor Meghan Giannotta have your inside look at Newsday's summer FunBook. Credit: Newsday/Howard Schnapp, Kendall Rodriguez, Drew Singh; Anthony Florio, Randee Daddona, Morgan Campbell, Debbie Egan-Chin

Get ready for sun and fun with NewsdayTV's summer FunBook special! From celebrating America's 250th birthday to a new ride at Adventureland, NewsdayTV's Elisa DiStefano and Newsday lifestyle editor Meghan Giannotta have your inside look at Newsday's summer FunBook.

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