BLAWNOX, Pa. -- Most of the residents displaced by a fire at a senior citizen high-rise in Blawnox returned home Thursday night.

VIDEO: Residents Return After Fire

The blaze started in a fifth-floor apartment at about 1:45 a.m. in the 700 block of Center Avenue.

One woman living on the fifth floor, Jean Guentner, 79, suffered second-degree burns, firefighters said. She was taken to the West Penn Burn Unit in stable condition. Friends said Guentner was set to celebrate her 80th birthday this weekend.

"(Firefighters) were talking to her," said Allegheny County fire marshal Bob Full. "I think they were going to try to climb over the railing."

Another woman who complained of chest pains was treated and released from a Pittsburgh-area hospital.

"I opened my entry door, and I saw all the smoke," said resident Rich Alvino. "I didn't know what the fire was. It smelled like it was electrical. So, I was going to go back to sleep but then I looked out. I saw lights, so I decided maybe I better not go to sleep. Might be sleeping for a long time."

Firefighters said the flames and heat were so intense that they had to go to the sixth floor to fight the fifth-floor fire.

"It was extraordinarily chaotic, but also very heroic," said Full. "On the sixth floor, they pulled a hose and went out on the sixth-floor balcony and squirted the hose on the fifth floor."

One woman, Melanie Casey, who just had knee surgery, told Channel 11 News that she crawled on the floor, trying to make it to Guentner's apartment. However, she said the smoke got too thick, so she had to turn around.

"I ran up the steps, and I opened the door, and it was just tons of smoke, and I couldn't kneel because of my knee, so I laid down on my side and tried to scoot against the wall to get to her apartment. I could hear her screaming," said Casey. "I couldn't breathe."

Another resident thanked Casey, who he said called his apartment. The man said if it weren’t for her, he wouldn't have known what was going on.

The cause of the fire is being investigated, but firefighters said it may be connected to cigarette smoking.

This was not the first time there was a fire at the high-rise. Two years ago, 120 people were displaced in a fire. No one was injured in that blaze.

Firefighters said the fire was caused by cigarettes in a trash can.