Three senior residents were hospitalized for smoke inhalation after a fire broke out at the Arlington Plaza-Sky Active Living facility in Arlington on Sunday morning, but the situation could have been far worse if not for the timely actions of a passerby.

A runner jogging past the facility at 6801 West Poly Webb Road noticed smoke coming from the apartments and began pounding on doors to alert the residents. One of the residents, Dave Boyles, directed the Good Samaritan to the fire alarm.

“They had come in the front door, and they were … beating on all the doors going down the hallway,” Boyles told NBC 5 DFW. “So I looked out in the hallway, and they said, ‘There’s a fire, there’s a fire.’ When I came out the front door I could see the black smoke coming up from over there.”

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When Arlington firefighters arrived on the scene, they saw flames coming from a second-story apartment balcony. They declared the situation a three-alarm fire so that additional firefighting units could respond and help quickly evacuate the building.

“There’s 86 people here, walkers, scooters. We needed the manpower to get them out just because the building did become pretty full of smoke,” said Lt. Adam Evans of the Arlington Fire Department, per Fox 4 KDFW.

Three residents required medical attention for smoke inhalation, but no one was directly injured by the fire, which was contained to the balcony of one unit. Firefighters say they believe the fire was accidental, but the cause of the blaze is under investigation.

Firefighters set up fans to clear the smoke from the building before allowing residents to return to their rooms.