Sugar dust sounds like an unlikely killer, but federal regulators were criticized two years ago for doing too little to stop it from triggering...

PORT WENTWORTH, Ga. — Sugar dust sounds like an unlikely killer, but federal regulators were criticized two years ago for doing too little to stop it from triggering explosions at industrial plants.

The threat was clear Friday in the gutted, burning remains of the Imperial Sugar refinery, a network of warehouses, silos and buildings eight stories tall connected by corridors of sheet metal.

A blast late Thursday collapsed floors, spread flames throughout the plant, buckled metal girders into twisted heaps and shredded sheet metal. Four bodies were pulled from tunnels underneath the rubble and crews were looking for at least four more workers. None was immediately identified Friday.

“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.

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“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 — several critically burned — were taken to hospitals as ambulances lined up a dozen at a time outside the refinery’s sole entrance road.

For 90 years, the refinery has been a core part of the economy in Port Wentworth, a city of 5,000 near Savannah. More than 100 people were working the night shift when the blast occurred.

Investigators were unable to determine what sparked the explosion. But John Sheptor, Imperial president and chief executive officer, said sugar dust in a silo where refined sugar was stored before being packaged likely ignited like gunpowder.

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 workers in grain silos, sugar plants and food-processing plants in the past 30 years. Most explosions are preventable by removing fine-grain dust as it builds up, experts say.

The U.S. Chemical Safety Board, which sent investigators to the plant Friday, concluded in a 2006 report that the Occupational Safety and Health Administration (OSHA) had no comprehensive regulation to prevent the blasts and its program “inadequately addresses dust explosion hazards.”

The board recommended OSHA issue a comprehensive industrial standard for combustible dust, but the agency did not do so.

Imperial Sugar employees gathered at a gymnasium for a company meeting Friday.

Employee Dana Claxton, 28, said the company promised its employees would continue to get paid. But that seemed little comfort to the workers hugging outside the gym, knowing some of their colleagues could still be trapped, or dead, inside.

“Everybody is upset about everybody,” said Claxton, who has worked at the plant for four years. “There’s a million jobs out here, but there’s not a million friends.”

The Port Wentworth refinery turns raw cane sugar into crystal sugar sold in supermarkets.