NEW YORK CITY — Police will release "harmless tracer gases" into subway stations throughout the city this summer to test the flow of noxious chemicals that could be used as airborne weapons.
The study is scheduled for July in underground and street-level locations along 21 subway lines and several dozen stations through all five boroughs to test the effects of airborne contaminants including chemical, biological and radiological weapons that could be released into the subway system, police said.
The exact subway lines remain secret for security purposes, police said.
"It is an effort funded through a grant from Homeland Security to determine the flow of toxic material through the subway system and also in the streets as well," Police Commissioner Raymond Kelly said during an unrelated press conference Wednesday. "What the public will see is perhaps as many as 200 detection devices. It will be done on three non-consecutive days in July.''
Researchers will release low concentrations of non-toxic gases known as perfluorocarbons, which are odorless and invisible.
During the study, commuters may notice boxes holding air-sampling equipment in subway stations, on street light poles and being carried by researchers.
A previous airflow study was conducted in Manhattan in 2005, but this is the first test to take place in all five boroughs, police said.
''If we get that type of material dispersed in the city, where does it go, how do you track it, is it transported more rapidly if something is done in the subway system?" Kelly added. "These are questions we've had out there for a while, and this will give us some answers.''
With reporting by Trevor Kapp