By ALISON SIDER

A man working on a maintenance project at Valero Energy's Ardmore, Okla. refinery died after being found unconscious Monday night, a spokesman for Valero said.

Valero spokesman Bill Day said the cause of death is unknown and is under investigation. There are no signs of any release, "no fire, no explosion, nothing like that," he said.

"[The death] is not believed to have been caused by the refinery at this point," Mr. Day said.

He said the refinery's emergency response team called an ambulance after the man was found unconscious, and the man was pronounced dead at the hospital.

The worker was employed by Cat-Spec, a contractor that was in the refinery doing maintenance work on the 85,000 bpd refinery's hydrotreater. Cat-Spec's main office was closed Tuesday evening.