One man has died and another has been hospitalized following an explosion at a refinery in Wynnewood.

Garvin County Sheriff Larry Rhodes says Billy Smith, a 34-year-old Pauls Valley man, was killed when a boiler in the refinery exploded about 6:20 p.m. Friday. Rhodes says Russell Mann of Davis was injured and remained hospitalized — his condition was not released.

Rhodes says the refinery had been shut down for planned maintenance and that the boiler was being brought back online when it exploded.

The sheriff said the investigation will be turned over to federal safety inspectors and CVR Energy Inc. of Sugar Land, Texas, the refinery owner.

CVR released a statement Friday saying it would assess the situation. CVR officials did not respond to phone calls and emails on Saturday.