Three employees at an ammunition manufacturing company were injured yesterday in a fiery explosion that rocked the central part of Stafford County, sheriffs deputies and emergency rescue officials said.

Two of the workers were flown to Washington Hospital Center. One of them is in critical condition with shrapnel wounds to her legs, abdomen and other parts of her body. Another is in fair condition with bruises to her face, hospital officials and a company employee said. The third woman was not seriously injured.

The blast, which occurred at Delta Frangible Ammunition LLC on Wyche Road, blew a hole through the side of the company's small building and left the interior a shambles, officials said.

"We could hear [the explosion] from the courthouse," said Fire Marshal Curt Alvis. A small fire accompanied the explosion and was extinguished by the building's sprinkler system, Alvis said.

The blast occurred while the plant was making bullets. Company officials said they are unsure what went wrong.

Delta Frangible President George Davis said the explosion was likely because of an employee error. "Something was done wrong," Davis said. "This doesn't happen spontaneously.

"It's like pumping gas," he added. "You do it every day, but accidents happen."

Davis said that employees are required to wear goggles and other protective gear, but that he was not certain whether the women who were injured were doing so at the time of the blast.

Davis said that he had talked with the employee who was in fair condition, and that she was doing well. He said he had not been able to speak with the more seriously injured employee. Davis declined to identify the injured employees.

"One of them appears much better than I feared," he said. "Right now I'm just worried about my people."

The company, which employs fewer than 10 people, manufactures an environmentally friendly lead-free bullet. Officials said that the damage would have been worse, and that additional explosions might have occurred if the firm made traditional bullets.

In addition to Stafford deputies and rescue squads, the Bureau of Alcohol, Tobacco and Firearms responded to the blast and remained on the scene yesterday afternoon to help investigate the explosion and make sure the area was safe.