It was a whirlwind from start to finish. Not only for marathon runners, but for volunteers too.

Leslie Adams, a nurse at Tufts Medical Center, was stationed inside the medical tent near the finish line of the race. Adams was hanging IV fluid for a dehydrated runner when she heard a huge crash.

"Then we heard from the announcer: 'Make space,'" she said. "We need to get all the runners out of the front of the tent. I look over and the gentleman who lost both of his legs was being run down the center aisle and I was like, 'Here we go, this is it.' That’s when the fear really started. Two seconds later someone else was doing compressions on another body, on a stretcher. I don’t know if that person made it. I was just terrified. In my mind I was thinking, 'Well, I’m here, I have to take care of these patients, I’m not going anywhere.'”

As a nurse in the pediatric intensive care unit, Adams is used to treating the critically ill, but her patients are usually stabilized in the emergency room before they reach her. This was different. It was raw. Her own safety was at risk. She’s never been so scared.

"Being terrified for my life and trying to reassure others that they’re going to be okay is a weird situation," she said. "In my head I was like, 'Oh my God,' and then I’m talking to a mom who’s holding her two kids sitting in a wheelchair, saying, 'It’s going to be okay.' I don’t know if it’s going to be okay, but I said that to try to calm her down because the look on her face wasn’t reassuring."

What reassured Adams were her three friends, also nurses and volunteers in the same medical tent. She saw them continue to take care of patients, and followed their lead. And then there was the voice of the medical tent coordinator, who called out directions from the microphone in them middle of the tent.

"I remember the announcer had a very calm, quiet voice," she said. "There was no sense of panic in his voice and he was able to relay information continuously. He was giving us direction every step of the way. I felt like there was never a moment of silence from him. That really guided me in what I was doing."

That guiding voice belongs to John Andersen, a middle school science teacher who’s been working as a marathon medical tent coordinator for 15 years.

"I honestly believe that I went into my teaching mode at that moment, and it was how am I going to make this situation as safe as I can for anyone who is here in the tent, and anyone who could be coming into the tent," Andersen said.

Doctors, police officers and firefighters would give directions to Andersen, which he would then relay to the rest of the tent.

"Nobody was yelling, no body was screaming, everybody was just doing what needed to be done as quickly as possible," he said.

After the first patient was wheeled in -- a ghost-white man with no legs below his knees, and belts holding up his legs to stop the flow of blood -- Andersen said the gravity of the situation became clear. He was afraid because he didn’t know where his wife was.

A charge nurse in the emergency room at Newton-Wellesley Hospital, Laurie Andersen was posted outside the medical tent. They had been married for 30 years and volunteered at the marathon together.

"I wasn't afraid, I don't know why I wasn't afraid," Laurie said. "I feel kind of weird about that... I knew that there were a lot of injured people, and I just went into action mode, and I didn't feel afraid."

Laurie said that after the second bomb, a lot of people started running towards her, while a wave of volunteers left the tent to help at the scene of the blasts.

"A second wave of people started to come out of the tent, and I basically told them to go back into the tent because by then there was injured coming in, and I figured they needed to wait for them to come to them, rather than run down the street," she said. "So I sent the second group back into the tent, and then I helped orchestrate who went in, how quickly, and made paths for the people who were sicker, so EMS could get through and into the tent and help the people who were walking and wounded and injured."

After the first rush of badly injured people were triaged, Laurie said she walked about ten feet into the tent and waved at her husband.

"She came in gave the 'hi' sign, and everyone who was around me pointed and told me, 'There she is, there she is, there she is,' which of course let my heart slow down a little," John said.

Both John and Laurie Andersen said a lot of lives were saved that day thanks to the amazing job done by their fellow first responders.

Brendan Kearney is second in command at Boston EMS.

"I think to the untrained public, they just see tons of resources coming to the scene," Kearney said. "But for the people who are involved in response, it is a coordinated response."

As soon as the blasts occurred, hospitals and private ambulance services were put on alert to prepare for mass casualties.

But it was in the makeshift emergency room in the medical tent that gave many of the victims the chance to survive.