Firefighters were working through the night to extinguish a blaze at a sugar refinery so crews that pulled four bodies from the rubble could resume the grim task of looking for more on Saturday.

At least four people known to be inside the Imperial Sugar Company refinery during the explosion were missing. Crews planned to bring in heavy equipment Saturday to remove debris as investigators continued assessing what sparked the blast that ignited a storage silo.

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Imperial Sugar was one of the largest, and oldest, employers in this tiny city of 5,000 just a few miles west of Savannah. The sudden blast that rattled the city late Thursday engulfed the refinery in flames.

Portions of it were still smoldering Friday night, Savannah Fire Capt. Matthew Stanley said.

Investigators were unable to determine on Friday what sparked the explosion as firefighters battled flames inside the vast refinery — a network of warehouses, silos and buildings eight stories tall connected by corridors of sheet metal.

"It really looked like a small war zone," Stanley said.

Imperial President and CEO John Sheptor said sugar dust in a silo where refined sugar was stored before being packaged likely ignited like gunpowder. Sugar dust can become combustible if it's too dry and builds up a static electric charge.

The result was as devastating as a bomb. Floors inside the plant collapsed, flames spread throughout the refinery, metal girders buckled into twisted heaps and shredded sheet metal littered the wreckage.

"There was fire all over the building," said Nakishya Hill, a machine operator who escaped from the third floor of the refinery uninjured but for blisters on her elbow.

"All I know is, I heard a loud boom and everything came down," Hill said. "All I could do when I got down was take off running."

More than 30 employees were rushed to hospitals as ambulances lined up a dozen at a time outside the refinery's sole entrance road.

Several were airlifted to a burn center in Augusta, 130 miles up the Savannah River. Many were in critical condition, including some who were placed on ventilators, said Dr. William Wessinger, the medical director at Memorial University Medical Center in Savannah.

Beth Frits, a spokeswoman for the Joseph M. Still Burn Center at Doctors Hospital in Augusta, said 16 fire victims transferred from Memorial were in critical condition and three were in serious condition.

By Friday afternoon, the first deaths were confirmed as firefighters pulled three bodies from tunnels that ran beneath the refinery; a fourth body was recovered later in the day. None was immediately identified.

Company officials refused to speculate on when the plant might reopen, saying structural engineers would need to examine the damage.

Sugar dust is so combustible that static electricity, sparks from metal tools or a cigarette can ignite explosions.

More than 300 dust explosions have killed more than 120 works in grain silos, sugar plants and food processing plants over the past three decades. Most are preventable by removing fine-grain dust as it builds up, experts say.

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