Authorities evacuated everyone in a 3,000 foot radius of the explosion due to fears that there would be more, and larger, blasts.
The explosion happened around 12:45 p.m. Wednesday at Scully Welding Supply at the intersection of Oak Avenue and MacDade Boulevard in Collingdale.
During that time, there was concern that the flames would hit two large propane tanks filled with gas. One of the tanks holds 33,000 cubic feet of propane gas, while the other has 18,000 feet of gas.
The American Red Cross said that approximately 200 residents were asked to leave their homes. Around 7:30 p.m., all residents were allowed back home.
Delaware County Emergency Services Director Ed Truitt says dispatchers received reports of multiple explosions, which were still ongoing when firefighters arrived.
Three workers were injured. One remains in serious condition at Crozer-Chester Medical Center. Four firefighters were treated for heat-related injuries.
Eamon O'Hara captured dramatic video of the explosions as they happened with his iPhone. He says the force of the blasts pushed him back, but he kept recording.
"It was crazy... scary. But it was giving me a little rush!" O'Hara said.
Tammy Scanlon, 38, who lives a few hundred yards across the railroad tracks from Scully's Propane, heard the explosions go on for about 30 minutes.
"It sounded like a car backfired the first time. It got worse," she said. "You could feel the dishes shaking in my house. It was just one after another."
Kimberly Bench, 47, said she felt the air suck in and out of her house and looked up to see a big piece of metal hurtling skyward during the blasts.
"We heard a big explosion. Our house rattled," she said.
Butch Cook, who manages a nearby a sandwich shop, said he heard a series of explosions, each one followed by flames, for about 20 minutes.
"You would hear a bang, and then the flames would be there," the 54-year-old Cook said.
Scully's is said to have suffered the brunt of damage in its backyard.
The damage, however, was not just contained to Scully's. The extent of the surrounding property damage is still unclear, but authorities say Kaiser's Automotive next door was gutted.
Mayor Frank Kelly initially said the fire may have begun when a worker was moving smaller propane tanks, but later clarified that was speculation. The actual cause of the fire is still under investigation.
Evacuees return home
Hundreds of evacuees were allowed to return to their homes a couple hours after the fire was extinguished.
Nervous residents along a 1-mile perimeter of Scully Welding Supply hurried out of their homes after emergency personnel came around telling everybody to get out.
"It was very scary, especially since my husband has emphysema and he's wheelchair and oxygen bound so we had to quickly get things together," Collingdale resident Helen Belcher said.
Emergency responders kept pushing residents further and further away out of concern the raging inferno could spread to other tanks including Robert's Oxygen Supply next door which contains three 2-story tanks containing oxygen, liquid nitrogen and carbon dioxide.
At the end of the day, the danger was over, and fear and tension was replaced by sighs of relief.
The Associated Press contributed to this report.