All hospitals train for events like Monday’s explosions after Boston Marathon, but they hope they won’t have to put it into use. But yesterday they did.

I arrived at Massachusetts General Hospital around 4 p.m., where 16 security guards stood between the entrance and the parking lot. Director of Emergency Services Alasdair Conn said some of the first victims from the explosions were taking here.

"The most severe patients arrived quickly by Boston EMS," Conn said. "And they were suffering from traumatic amputations, if you like, their legs were blown off. Those are the ones that basically were immediately evaluated and then taken to the operating room."

Conn said that the hospital upgraded its disaster response a few years ago to prepare for these types of events.

"We obviously have a limited experience of explosions in an urban area," he said. "The Israelis, unfortunately, have this several times a year, and we asked their disaster response teams to come and help us upgrade our disaster response and I'm very pleased that we went through that orientation and additional training. It's worked well today."

At Brigham and Women’s Hospital, where more of the victims were taken by ambulance, security was also tight. Three guards holding assault rifles blocked the hospital entrance. Only family members and employees could enter the building.