The Gas Company and Redondo's officials inspect the roof over part of the Waipahu factory where workers were evacuated today after hearing some kind of explosion. BRUCE ASATO | The Honolulu Advertiser

The Honolulu Fire Department responded to the scene, but no smoke or fire was visible an hour later.

Kendrick Ho, Redondo's production manager, said officials were still trying to figure out what happened.

He said the injured employee was struck in the head by a falling tray but was able to walk away.

Bryan Cheplic, spokesman for the city Emergency Services Department, said one person was treated at the scene for minor injuries.

Employee Larry Bagay was among the nearly four dozen employees sitting across from the plant awaiting further instructions.

"We heard a big bang in the smoke house," Bagay said, adding, "that's where we cook all our hot dogs."

"It was really loud."

Soon afterward, he said, their quality control manager told them to leave the building until officials knew more about what had happened.

At 11:20, Ho told employees they could go to the locker area and pick up their belongings and then go home.