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A strong cellphone battery and the perseverance of emergency crews on Monday morning led to the dramatic rescue of a young woman who sprained her ankle and could not walk her way out of an enormous remote railyard on the South Side.

The woman, in her early 20s, was on her way somewhere when she decided to take a shortcut through the yard south of 39th Street and near Damen Avenue, said Chicago Fire Department spokesman Larry Langford.

As she stepped through the huge industrial rail area, she hopped over a fence but tumbled and came down hard on her ankle, spraining it, Langford said.

Lying there, unable to move, she began calling 911 at 10:13 a.m.

“She said she couldn’t walk and was injured and needed medical assistance,” Langford said.

An ambulance and fire engine was sent to the area she thought she was — south of 39 and east of Damen.

She stayed on the line with 911 operators, but first responders encountered a major problem: Their vehicles could not get inside the railyard, there was no access.

Crews including a battalion chief were sent in on foot.

“They were literally walking around the railyard, looking for her,” Langford said.

They started asking if she could hear the chief hitting the air horn blaring and if she could she could hear a train that had just passed by.

“Time was going by and they couldn’t find her,” Langford said.

At one point she said yes, she could hear the airhorns getting closer but then the horn’s sound was fading. “So we’re passing her,” Langford said.

After enlisting the help of the Fire Department’s helicopter, they asked her for her description: “Are you out in the open? Are you underneath anything?”

She told then she was wearing blue and within five minutes after sending the helicopter in, their luck changed — she could see the helicopter near 43rd Street and at 11:40 a.m., they finally found her. As it turned out, they’d been looking too far north, Langford said.

The railyard police stepped in and helped with their next hurdle: getting inside.

“We get a call from the railroad police, who knew how to get inside with their vehicles in there. They put their SUV in there, drove out into the yard, and lifted her into the SUV,” Langford said.

Fire’s ambulance 68 was waiting on the street at 41st and Ashland Avenue, and she was carefully moved from the SUV.

After paramedics examined her, she was taken to the University of Illinois Hospital, where she is recovering from a bad sprain.

Langford, who was on the scene when she was rescued, didn’t talk to the woman but saw her.

“She looked relieved but she was kind of worn out. She was out there for over an hour. She looked kind of concerned and at the same time she was happy she was found,” Langford said.

“I’m sure she’s happy her phone has a good battery.”

Langford said it was fortunate the incident happened during the daytime and it wasn’t cold or they would have had to use heat sensing cameras to find her.

“She was where nobody would have seen or heard her from the street,” Langford said. “She is going to be OK.”