A medical worker rushed to escape from a ‘labyrinth’ of offices in Tulsa.

Gannon Gill was wrapping up an appointment with a new patient on Wednesday when a loud noise startled him. A few seconds later, he heard it again.

Mr. Gill, a physician assistant and a hunter, recognized those sounds as gunfire.

“There was an initial ‘What was that?’” said Mr. Gill, who runs an orthopedic urgent care clinic at the facility in Tulsa, Okla., that was the site of a deadly shooting on Wednesday. He turned to his patient and said: “Let’s go. I don’t think this is good.”

He would later learn that some of his colleagues hid in bathrooms or storage closets. He guided his patient through the “labyrinth” of exam rooms and interlocking hallways, away from the sound of the gunfire. They ran into a small group of colleagues, who joined them.

Mr. Gill crouched, moving quickly toward the closest exit. He and the group made it through the front door of the office and hustled to the parking garage. They were out in less than a minute.

Once in the garage, he discovered his phone in his pocket and called his wife. “Don’t freak out, I’m alive,” he recalled telling her. He asked her to bring his car keys, which he realized he had left behind.

It became clear to Mr. Gill the area was safe and he stayed in the garage with his colleagues, where they called others they couldn’t account for.

One man in the garage, a patient, told Mr. Gill that he and his wife had encountered the gunman during the attack.

“The shooter told him and his wife to leave and he was not there for him,” Mr. Gill said.

During a phone interview, Mr. Gill said he had a hard time remembering some details about a “pretty scary” day.

“You see this stuff on television or the news,” he said, “but you don’t think its ever going to happen in your workplace.”