According to Felicia Gans of the Boston Globe:
South Boston residents can expect increased police activity Tuesday morning as public safety and transportation agencies carry out chemical incident drills.
The exercise will train authorities on how to respond if there is a chemical release in a subway station. Agencies including the MBTA, along with Boston police, fire, and Emergency Medical Services will participate.
The training takes place from 10 a.m. to noon at the Paul S. MacMillan MBTA Emergency Training Center on Foundry Street, though state transportation officials warned there could be increased activity in the area as early as 8 a.m.
Dozens of volunteers will also be in attendance, playing the role of subway customers in the exercise.
The state transportation department is working with representatives from city and state departments, the MBTA, Amtrak, the FBI, and several other agencies to coordinate the chemical incident exercises.
For more information, residents can visit the MassDOT website, blog, or social media page
Video from 2014 Boston Urban Shield Exercise