According to safety officials with the Georgia Department of Labor, the blasts might have occurred when workers tried to unseal one of two 9-foot-tall, 48-inch-wide round pressure vessels. The tanks contain byproducts from the Amodel unit's polymer production.

Some of the victims were preparing to clean the vessel - also known as a ``knockout pot,'' said Labor Department Inspector Carl Spitzer, who visited the site Tuesday afternoon. The workers had loosened a few of the bolts on the head - a cap sealing the tank. Then the head blew off. Investigators are still trying to determine the cause of the two explosions.

Heinrich ``Heins'' Kohl, 25, and George Sanders, 42, were apparently at ground zero of the explosions and died instantly. John Rowland, 35, was pronounced dead more than an hour later at Medical College of Georgia Hospital.

All three victims were operators at the plant. Plant officials said they were shutting down the unit for routine maintenance and repairs before their deaths. Hot water had been flushed through the pipes, and the system was cooling down.

The waste tank normally operates at 108 pounds of pressure, said Jerry Hancock, the department's boiler pressure safety supervisor for the safety engineering division in Atlanta. Before being opened, the tank's gauge should have read zero.

Mr. Hancock said plant workers reported it had spiked to 5. Mr. Spitzer said the pressure was likely between a half-pound and one pound before it blew.

``That's really a low-pressure vessel, and that's what's got us stumped,'' he said.

Two explosions occurred simultaneously about 2:35 a.m. at the plant at the corner of Tobacco and Clanton roads, one of several sprawling industrial facilities that pepper the southern end of Richmond County.

Damage to the structure was minimal, but Syltherm, a heat-transfer fluid that keeps pipes hot to prevent polymers from hardening, leaked and fueled a fire that took hours to put out.

The findings about the vessel mishap are only preliminary, and a definitive cause of the disaster has not been determined, Mr. Hancock cautioned.

``It's about like guessing, but that's what it appears to be,'' he said.

Three other Amodel workers were at the other side of the unit at the time of the blasts. Those the inspector interviewed ``just said they heard a loud bang,'' he said.

Only the dead saw what happened, which is making the investigation difficult, Mr. Spitzer said.

``They took it to the grave with them,'' he said.

Pam Barbara, the plant's site services manager who is acting as spokeswoman in the wake of the tragedy, said the company could not comment on the Labor Department's findings until its own internal investigation is finished, which could take weeks or months.

The federal Occupational Safety and Health Administration and the U.S. Chemical and Safety Hazard Investigations Board are also investigating.

Amodel and all other units at the plant - which makes heat-resistant plastics used in car engines and medical equipment - were shut down Wednesday. They will likely stay that way until after the three men's funerals, Ms. Barbara said.

``We wanted to get our people refocused,'' she said. ``When you have distracted employees, you don't want to be operating on the other units.''

Despite the shutdown, there is still cleanup work and equipment monitoring for the plant's 200 employees to do, Ms. Barbara said.

``Plus, we wanted to give them counseling to help them deal with the situation,'' shesaid.

Plant Manager Scott Savage, human resources officials and counselors spent Wednesday visiting the families of the men killed in the explosions.

Richmond County Emergency Management Agency and Rural/Metro Ambulance agents assisted plant personnel Wednesday in dealing with issues and in the cleanup of some bio-hazardous materials, EMA Director Dave Dlugolenski said.

Investigators were gathering data from equipment and gauges that will be analyzed in the coming weeks, Mr. Dlugolenski said.

``They're still in the fact-finding mode,'' he said.

Staff Writer Sylvia Cooper contributed to this article.

Reach Johnny Edwards at (706) 823-3225.