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PHILADELPHIA, PA (CNN) -- A man risks his own life to save a fellow subway rider in Philadelphia. The victim's fall onto the subway tracks was caught on camera. Good Samaritan describes his quick reaction as a basic instinct.

Chris Knafelc says, "I can't imagine not helping someone in that situation, like I can't imagine that."

In SEPTA surveillance video, you can see the victim, for whatever reason, walk right off the platform at the Cecil B. Moore subway station. He's sprawled across the tracks, just inches from the third rail, which if touched, will electrocute a person.

Still, witness Chris Knafelc jumps down four feet to help. He says, "I just wanted to stabilize his neck because he kept trying to move."

Knafelc stayed with the victim, but he knew time was critical; the subway runs every seven minutes.

So he shouted to nearby passengers to tell SEPTA personnel to shut down the southbound lines. He says, "I had a plan if a train came. I was going to roll him underneath, you know. Like where you stand, like underneath the ledge or if I couldn't I was going to ask someone to jump down and help me roll him."

Chief Thomas Nestel with SEPTA Police says, "There are bad scenarios that could have happened here and didn't happen because a person that was unknown to our victim jumped into the track and saved his life."

Firefighters arrived and moved the victim off the track. He was taken to Temple University Hospital where he's in stable condition.

Knafelc is being hailed for the compassion he displayed. But the 32-year-old says it's simply how he was raised. He says, "There have been people there for me when I needed somebody and these people I can't pay back, so the next best thing would be to pay it forward."

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