WASHINGTON -- An executive at a sugar company faulted for a deadly refinery accident in February said he found such "shocking" and "disgraceful" conditions at the Georgia plant last year that he warned his superiors that a fatal disaster was likely.

But Imperial Sugar Co. executives responded that he was being overzealous and told him to back off, he said. A month later, an explosion ripped through the plant in Port Wentworth, Ga., killing 13 workers and injuring dozens more.

"It was without a doubt the dirtiest and most dangerous manufacturing plant I had ever come to," said Graham H. Graham, who toured the facility shortly after being hired in November as Imperial's vice president of operations. "I stated that I believed a fatal disaster would befall the refinery if a fundamental change in the way the plant was operated did not take place."

Graham's comments came at a hearing before the Senate Health, Education, Labor and Pensions subcommittee on workplace safety, which is reviewing the accident to determine if tighter regulations are needed to protect workers from combustible dust hazards.

Investigators said the explosion was fueled by excessive accumulations of dust that was probably ignited when a large bucket used to haul sugar in a silo elevator broke loose and struck the metal siding, causing a spark.

Last week, the Occupational Safety and Health Administration proposed nearly $9 million in fines against Imperial for what it said were willful and egregious safety violations. If sustained, the fines would be the agency's third-highest on record.

OSHA said criminal charges are also possible.

Imperial, based in Sugar Land, Texas, is contesting the citations. CEO John Sheptor declined to appear at Tuesday's hearing but issued a written statement defending the company's safety record. The company also released e-mails showing that Graham reported progress after his initial evaluation, saying in one January e-mail, for example, that workers had made "enormous improvement."

In an interview Monday, Sheptor said Graham has "exaggerated numerous things regularly about our facilities" and suggested that Graham was trying to protect himself from being blamed for the accident.

Graham said Tuesday he was hired to oversee general operations and he intervened with safety warnings even though he is not the top safety officer.

He told lawmakers that the Georgia refinery -- the second-largest in the U.S. -- was littered with debris and sugar dust. Electrical equipment had missing safety covers, and motors and controls were encrusted with sugar, he said. Fire protection gear was "sheathed in dust so thick it was impossible to determine if it was operable," he said, and employees said they could not remember the last time they participated in fire drills.

Graham said he found similar conditions at an Imperial refinery in Gramercy, La., which was also cited in OSHA's investigation.

He acknowledged that conditions improved after his initial reports, including the immediate firing of the Georgia plant manager. But he said he warned superiors that the job was not finished.

Democrats said the blast -- the latest in a series of fatal dust accidents in recent years -- highlights the need for new federal safety regulations. The House passed legislation in April that would force OSHA to adopt new standards specifically targeting dust.

But OSHA head Edwin Foulke told the panel that the Imperial findings bolster the Bush administration's position that regulations aren't necessarily the cure. Although OSHA has not ruled out a new standard, he said, the investigation shows that existing regulations are broad enough to cover dust hazards.

"It shows ... that the system works," he said. "It wouldn't have mattered if we had a combustible dust standard. This accident would have happened."

Independent safety experts disagreed, arguing that the general violations that OSHA cited -- such as for poor maintenance -- do not provide enough guidance to address the specific hazards posed by dust and that employees don't understand the severity of the threat.

John Bresland, chairman of the U.S. Chemical Safety Board, said the Georgia accident could have been prevented with stiffer regulations. In a 2006 study, Bresland's agency found that 281 industrial dust fires and explosions between 1980 and 2005 caused 119 deaths and more than 718 injuries. Since the study, he said, 82 additional dust accidents have occurred.

"OSHA has failed to respond proactively," said subcommittee Chairwoman Patty Murray, D-Wash. "These penalties come far too late for the 13 workers who died."