PORT WENTWORTH, Ga. -- Investigators believe sugar dust may have caused Thursday's sugar refinery explosion near Savannah.

Sugar dust is considered a combustible dust, according the U.S. Occupational Safety & Health Administration's Web site.

According to the Handbook of Sugar Refining, sugar dust comes from various sources, including rotary driers, bucket elevators, and sieves. The handbook said faulty operatiojn of vaccum pans, which are used to make sugar, and an increase in sugar temperature can produce even more sugar dust.

Static electricity, sparks from metal tools or a cigarette can ignite explosions, officials said. Sugar dust is suspected of sparking a nonfatal explosion last summer at a factory in Scottsbluff, Neb., and one that killed a worker in Omaha, Neb., in 1996.

Imperial Sugar, based in Sugar Land, Texas, acquired Savannah Foods & Industries, the producer of Dixie Crystals, in 1997. The acquisition doubled the size of the company, making it the largest processor and refiner of sugar in the U.S., according to the company Web site.

Imperial markets some of the country's leading consumer brands, Imperial, Dixie Crystals and Holly, as well as supplying sugar and sweetener products to industrial food manufacturers.