Around 2:50 p.m. at Charles/MGH as cops swarmed the station looking for somebody who might have robbed a bank in Central Square.

UPDATE: Cambridge Police report:

Transit Police report arresting somebody too young to have his name released for the botched robbery attempt last week that ended with him being chased out of Charles/MGH by a group of fed-up commuters.

The teen was scheduled for an appearance in Boston Municipal Court's juvenile session on a charge of assault with intent to rob, police say.

Update: Arrest made.

A woman's screams from one end of the outbound Charles/MGH platform got the attention of other people waiting for the train shortly before 9:30 this morning - and some of them started running after the guy who'd just grabbed her purse. Sarah Connors reports:

Transit Police say this guy wasn't going to let the locked doors of a closed Charles/MGH last Friday stop him from getting up onto the platform for a train that wasn't coming because it was 1:46 a.m.: He kicked in a panel of one of the station's doors, went upstairs and after waiting for awhile, took a piss onto the tracks.

Naturally, they'd like to have a word with him.

Signal problems on the Longfellow or track problems at Charles/MGH, take your pick of announcements.

Bostonians had their choice of venues for standing around this AM, such as Andrew. Photo by Chris Wright.

Fire on the inbound tracks between Arlington and Copley around 7:40, Jay Joynes tweets. At first, the T shut Arlington station because of heavy smoke, but shortly after 8 a.m., it shut down all Green Line service downtown. And shortly after 8:30, the T began evacuating trolleys stuck in the tunnel near Hynes and Copley stations.

The T eventually sent in some shuttle buses between stations to the west and downtown, but many commuters didn't wait. As Gracetopia tweets:

I now feel like one of the army of the commute, as I walk from Kenmore to downtown with my fellow MBTA refugees.

Lindsay Douglas, though, was one of the people who stayed behind at Kenmore:

I've never seen chaos like this. Coldest day of the year + the MBTA shuts down the green line. Yelling+angry people.

And because misery loves company, an inbound Red Line train died not long after at Charles/MGH, Rob Grover tweets. Later, another train died at Porter. Around 9:20, another train died, inbound at Andrew.

UPDATE, 6:10 p.m. Firefighters confirmed fire is out, get off tracks, T to restore power.

Today's track fire is by Charles/MGH and, of course, it's causing delays - not to be confused with the morning delays caused by signal problems as JFK/UMass (maybe the T needs to stop giving stops dual names).

This is the first Red Line fire since last Thursday.

The morning after No Pants Day, Gretchen Bostrom tweets (don't read if eating):

Just witnessed a guy blow snot into his hand & wipe it on a bench at Charles MGH station, Alewife side. Seriously? No wonder we get sick!

Now I will NEVER sit on a public bench if I can help it!

I think I'm going to be that crazy lady who buys small tissue packets at CVS and hands them out to people I see sniffling.

Meanwhile, over on the Orange Line, Cara reports this morning:

The Globe reports on yesterday's dramatic Red Line rescue and says the T is reacting to "poor decision making" that led to deadly holes being covered with Bounty towels plywood by ordering all such sheets replaced with steel.