NYPD to test for subway gas attack risks

The NYPD at 8 a.m. will conduct an urban airflow study that entails pumping low-concentrations of a harmless, invisible and odorless gas at several subway and street-level locations in Manhattan for 30 minutes. 

Further, air sampling will take place across the five boroughs. The test, the first of three, will help the NYPD determine the risks that airborne chemical, biological and radiological weapons can pose.

The NYPD will give a 24-hour notice before the remaining testing days.