Dean McAuley had found a path to safety, but he didn’t leave. As his two friends followed the police away from the Las Vegas gunman’s view, one called back to him: “You’ve got to come with us.”

He replied, “I’ve got to go to work,” he said at a news conference on Wednesday.

Mr. McAuley, a firefighter from the Seattle area who went to the country music festival each year with friends, ignored warnings that bullets were still flying. He got gloves from a medical tent and helped bring two women back to the tent. He then helped Natalia Baca, 17, by operating a tourniquet and helping to put an IV in her arm.

She had a hard time breathing, but was calm. He told her to trust him, and said he wouldn’t let anything happen to her.

He let her use his phone to call her father, telling him that she would be O.K. After a man offered his car to take them to the hospital, he kept her calm by showing her pictures of his wife, son and dog.

A day later, after he spent several more hours triaging patients at the hospital, he made it home to Washington and “squeezed the heck out of my wife.” He was avoiding his phone, but was relieved to get a text message from Ms. Baca’s father: “You saved my daughter’s life.” Ms. Baca and her twin sister were both O.K.