(CNN) -- Inside Moore Medical Center's emergency room, Dr. Stephanie Barnhart had been monitoring the weather all afternoon. A tornado watch was in effect, but that was almost commonplace for this time of year in Oklahoma.
The first "code black" emergency alert came shortly before 3 p.m. on Monday. The second notified the staff a tornado had touched down in the nearby town of Newcastle. Barnhart and her team jumped into action.
The doctors quickly moved all 30 hospital patients to a clinic in the center of the hospital. They used mattresses and blankets from gurneys in the hallway to cover themselves in hopes of preventing head injuries.
For 15 to 20 minutes, they waited anxiously, watching on TV as the massive tornado moved within 2 miles of their location.
Then the power went out.
"We were hearing it, and we knew that it was coming for us," Barnhart remembers.
The tornado ripped through 17 miles of central Oklahoma. At least 24 people, including nine children, were killed, according to the state medical examiner's office.
The second floor of the medical center was reduced to rubble. Lampposts and other items from the streets were hurled through the walls of the ground floor. Cars, including Barnhart's, are now piled upside down and sideways in the parking lot. It looks a lot like a junkyard.
"It's pretty amazing that we even walked out alive," Barnhart told CNN's Dr. Sanjay Gupta.
One of the biggest concerns in a tornado is shrapnel, Gupta says. A loose object or anything that's broken by the force of the storm's winds can cause a penetrating, and potentially deadly, injury.
Looking at the destruction, it's hard to believe some patients walked out of the medical center without a scratch. The mattresses and blankets helped protect them from the worst of the storm.
Huddled inside the hospital, Barnhart says she didn't realize how much damage the tornado had caused until she walked outside and saw the bowling alley across the street -- or saw where the bowling alley used to be.
Barnhart, 34, is a tiny blonde bundle of faith. She called her husband as soon as she could get cell reception after the tornado passed to tell him she loved him. She says she wasn't really concerned about her own safety during the storm, but worried about friends and family -- who all thankfully made it through OK.
"We've been blessed by that. I know there are lots of families that have been devastated by this, and we are definitely praying for them," she says.
Barnhart went back to work Monday night at one of the area's other hospitals, where patients at Moore Medical Center were evacuated after the tornado passed.
She's received many thanks for her quick thinking, but says it's difficult to take credit.
"I was just doing my job, and I knew what I had to do," she says. "It's Jesus that helped us and saved us, and I know that he was with us."
CNN's Danielle Dellorto contributed to this story.