Georgia's senators are urging the federal government to launch an investigation into the explosion at the Imperial Sugar Co. refinery which killed seven people and left another missing.

Sens. Johnny Isakson and Saxby Chambliss sent their plea to Labor Secretary Elaine Chao and William Wright, the interim executive of the U.S. Chemical Safety and Hazard Investigation Board.

Federal agencies have already deployed investigators to the site, but the senators are asking for a "complete and thorough investigation of the incident," according to the letter.

"It is imperative that the federal government begins work quickly to determine why this accident happened so we can avoid another tragedy," said Isakson.

Added Chambliss: "We need to ensure that we know how this happened and how future situations can be prevented."

An explosion of sugar dust as powerful as a bomb blast is thought to be the cause of the Feb. 7 blast. Emergency crews were able to snuff out the fire at the plant's main building Wednesday, but the blaze persists at the refinery's 80-foot silos. Local crews had to call in a specialized team with powerful equipment to assault the blaze.

The refinery is located on a 160-acre site on the Savannah River upstream from Savannah. The plant is 872,000 square feet, and 111,000 square feet — about 12 percent — was destroyed, said company spokesman Steve Behm.