Port Wentworth, Ga. ? Volatile dust was blamed Friday in an explosion that leveled a sugar refinery, and crews pulled four bodies from tunnels beneath the mangled mass of metal and beams left by the blast.

At least four people known to be inside during the explosion were missing. Savannah police Sgt. Mike Wilson said no attempts would be made to find more bodies until today, when heavy equipment will be brought in to remove debris.

Search efforts were slowed by the instability of what was left of the refinery, gutted by flames and wracked by the impact of the blast itself.

Anxious families of the night-shift workers at the Imperial Sugar plant gathered at the parish hall of a Catholic church across the street and wept as officials relayed grim news from the plant.

Investigators were unable to determine what sparked the overnight 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.

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 with 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.