JACKSONVILLE, Fla. -- With the fire out and the bodies of four men killed recovered from the remains of the chemical company that exploded and was consumed by an inferno on Wednesday, the focus of efforts at the scene shifted to finding a cause of the blast and rebuilding the neighborhood.

Investigators from four federal agencies joined Jacksonville homicide detectives and the state fire marshal at the scene of Wednesday's massive explosion and fire that took four lives and sent 14 others to area hospitals.

"It looked like one of those roadside bombs you see in Iraq you see on TV," said Anthony Faranella, who was working just 500 feet away when the building exploded. "The destructive power was just phenomenal."

Teams from the U.S. Chemical Safety Board, National Safety and Health Administration, the National Transportation Safety Board and the Department of Alcohol, Tobacco and Firearms arrived at what's left of the T2 Laboratories facility.

Thursday morning, Jacksonville Fire-Rescue officials removed the last two bodies from the site and identified the four people killed -- all employees of T2 Labs, one of whom was a co-owner of the company.

"This particular accident most likely has the highest rank of any we've looked at in 2007 and one of the highest that the agency has investigated," said Bob Hall of the federal Chemical Safety Board. "This is a very serious accident, compared to what is normally seen in the industry."

Businesses in the immediate area remained closed while safety inspectors assessed the structural integrity of the buildings. One neighboring facility had a wall blown out and the roof collapsed.

"It has the appearance of somewhat of an earthquake, where the buildings have been shaking, literally," Jacksonville Sheriff's Office spokesman Ken Jefferson said.

An estimated 1,000 people who work in the area were kept out Thursday, but a few of the business owners were allowed to inspect their property.

"We're about 300 yards from where the explosion was and it's heavily damaged," said Brian Almony. "A lot of glass broken out and all the walls inside buckled."

JEA crews were restoring power in the area and a CSX rail crew was making repairs to damaged tracks behind the explosion site. There was no word on when the area would be reopened.

The 1:30 p.m. explosion at the chemical manufacturing plant on Faye Road -- about one block from the coal-fired electric plant on Heckscher Drive -- was felt by people several miles away and the column of black smoke could be seen from as far as 70 miles away in coastal Georgia.

"There was like this tremendous boom like I've never heard in my life," said Shannon Story, who works nearby. "Everything shook in the building, the power went out, light bulbs fell from ceiling. We all evacuated as fast as we could."

Witnesses described a flash, an explosion and a mushroom cloud above the plant that manufactures chemical solvents and fuel additives.

When the first firefighters arrived, steel and debris were flying through the air.

"The incident is so violent and the fire is still so volatile ... we have not been able to ascertain directly yet what materials are present," Jacksonville Fire-Rescue spokesman Tom Francis said in announcing that a one-half mile radius was evacuated.

More than a dozen victims were transported to four area hospitals, where they were decontaminated upon arrival. Of the 11 patients taken to Shands-Jacksonville Medical Center, one was in critical condition, three fair, seven good and one had been released. Doctors said most of the injuries were from broken bones and chemical exposure.

By late afternoon, with the fire under control and the air quality declared safe, the evacuations were lifted and officials began assessing the damage.

"Nothing there resembles a building," Mayor John Peyton said. "It's amazing when you see the scene that there wasn't more loss of life."

Neighboring businesses were also damaged, one losing a wall and the ceiling collapsing. Shrapnel from the explosion fell at the JEA plant a quarter-mile away.

Byron Evetts, an engineer working at the JEA plant who is also a trained rescuer, rushed to the scene to try and help.

"There were large, structural beams lying hundreds of yards from the scene. It looked like a war zone," Evetts said.

Faye Road between Alta Drive and New Berlin Road remained closed to all but official traffic Thursday morning. Officials said the closure could last some time.