BOSTON (WHDH) -- Scientists are teaming up with the MBTA this week to simulate a chemical or biological terrorist attack.

Boston is getting federal money to understand how gases might move through tunnels in the event of an attack.

“This will help the first responder,” said Dep. Chief Lewis Best, MBTA transit police.

The MBTA was chosen, along with Washington D.C., for the federal experiment.

“And we think by studying the oldest system in the U.S. and one of the more modern systems that we can apply broadly the lessons learned that from these experiments to other transit systems across the country,” said Teresa Lustig, Dept. of Homeland Security.

The teams are releasing and tracing the movement of odorless, nontoxic gases.

“Where we are in today’s world we know that transit systems have been attacked by terrorists and this is just another preparedness step to be ready for such an incident and to enhance the overall security,” Dep. Chief Best said.

But it isn't done overnight.

"It takes two to three months to get all the results back. We have some results immediately, that we use to get just a general feel for how the test is going,” said David Brown, research scientist.

And sometimes that leaves them with more questions that need to be answered; a long and tedious process.

Testing will continue through the end of the week, at off-peak hours and should not disrupt commuters.