Federal researchers will release nontoxic particles and gases into the New York City subway this month as a part of a study on airborne terrorism threats, officials announced Sunday.

According to Daily News, Researchers from the Homeland Security Department and the Massachusetts Institute of Technology aim to find “actionable data for emergency preparedness authorities,” according to an advisory from the Metropolitan Transportation Authority.

The particles and gases that will be used in the study are designed to imitate biological and chemical agents, authorities said. The scientists will set up air testing devices at dozens of locations across the subway from Oct. 18-29 to conduct the study.

Fox5 News stated that this isn’t the first time researchers have released non-toxic particles and gases into the New York City subway system. Several subway stations will be tested on five random days within the next two weeks. “The key here is if you believe your adversaries want to take down the core central transit system, then how would they do that?

This would be one of those ways,” said Balboni. Balboni explains the particles and gases used in the study will imitate the movement of biological and chemical agents in a densely populated urban environment.

Those gases will then be tracked, allowing researchers to understand the relationship between airflow on street level and in underground environments. “This is just a proactive stance by MTA to ensure ppl are comfortable that airflow has been tested,” said Balboni.