Boston's subway system will soon be sprayed with non-hazardous bacteria to test new sensors for identifying biological attacks. The test is part of the U.S. Department of Homeland Security's Science and Technology Directorate's (S&T) Detect to Protect program, which is designed to identify a biological attack within minutes.

In 2009 and in August this year, inert gasses were released in the Boston subway system as part of an initial study to determine how particulates flow through the subway and where the best locations for sensors were. Now that the sensors have been placed, killed Bacillus subtilis will be sprayed in small quantities throughout the subway tunnels. The bacterium being used is common and considered nontoxic to humans even while it's alive.

“While there is no known threat of a biological attack on subway systems in the United States,” S&T Program Manager Anne Hultgren said, “the S&T testing will help determine whether the new sensors can quickly detect biological agents in order to trigger a public safety response as quickly as possible.”

The released particles will dissipate quickly but will provide invaluable data for the project, according to a Homeland Security Department press release.