WEST CARROLLTON, Ohio -- A leak of ignitable liquid led to the midnight explosion that rocked West Carrollton and surrounding communities on Monday.

Authorities said the liquid came into contact with gas-fired boilers in or around the laboratory at Veolia Environmental Services on Infirmary Road.

Investigators said they found no evidence of criminal intent during the investigation.

Two people were injured during the blast. One was treated and released from a local hospital. The other victim remained hospitalized on Tuesday.

Firefighters made a decision to let the fire burn itself out, in part, to avoid runoff into local streams and rivers, but later foam was applied to the fire.

The force of the blast shattered windows near the plant and sent flames and a huge plume of black smoke into the air around midnight. One neighbor told News Center 7, "Boom! Everything fell off the walls. I didn't know if a plane had crashed in my front yard. My second thought was the plant over there."

The blast leveled two buildings on the property, the laboratory and a building that had chemical tanks in it. The blast also shattered windows and caused other damage to nearby homes.

The Ohio Environmental Protection Agency and the U.S. EPA were called to the scene to investigate.

Darek Teeters, General Manager of Veolia ES Technical Solutions said, �The safety of our employees and neighbors is our top concern. Six employees were on site at the time of the explosion. Of that number, four employees were sent to the hospital � one was evaluated and released; one was treated and released; and two were admitted. Of the two employees hospitalized, one suffered burns and the other a pelvic injury. All of our employees were evacuated safely."

People as far away as Clayton reported feeling the explosion, and the flames could be seen for miles.

One woman who lives near the plant, Evelyn Lowrie, said the explosion shook her house very hard. Lowrie said, "When it hit, it hit hard. Didn't really know what it was."

EPA officials said Monday afternoon that there was no health risk to residents in the area. "Safety is a very high priority. We are working with authorities to keep our neighbors notified of the situation," said the company's general manager.

Stay with WHIOTV.com for continuing updates, and follow us on WHIOTV's Twitter Page