OMAHA, Neb. -- Authorities continue to investigate a fire that ripped through a south Omaha community earlier this week.

The Omaha Fire Department continued to put out hot spots throughout Tuesday, a day after the Nox-Crete chemical company's building on S. 20th Street was destroyed.

What started as a fire became more after an explosion of propane tanks and cloud of smoke that enveloped most of Omaha.

"We had a few propane bottles that did explode," OFD Fire Chief Scott Fitzpatrick said of the three-alarm fire. "Crews backed up a little more, evacuated more people from the area once we knew what was inside the structure. And throughout the next few hours during the fire, we had several explosions that happened inside the building."

Nox-Crete is a company that makes chemical solutions for concrete products and these flammable chemicals were what spread the fire. According to Fitzpatrick, the building was empty when the flames started.

Sergio Robles, Risk Reduction Specialist for the Omaha Fire Department, explained that although they kept the fire under control, they decided to evacuate residents due to its proximity to residential areas.

"We put up an announcement on social media that people had to evacuate their homes because of the magnitude of the fire," Robles told Telemundo Nebraska. "And since the fire was very close to neighborhoods, so we wanted to make sure everyone was safe.

Approximately 15 people evacuated their homes and went to the Columbus Community Center. Now there is no order to evacuate and residents can safely return to their homes.

“In that fire, there are a lot of chemicals we are unaware of what they were. So the air quality is what we were concerned about,” Jennifer Rohda with Nebraska Regional Poison Control told news partner WOWT.