HOUSTON— Five employees have been released from a hospital after a Valero Houston Refinery sulfur tank fire early Monday.

Valero Energy Corp. spokesman Bill Day said the workers were taken to the hospital for evaluation, but the sulfur release was quickly contained. Three were contract employees from the refinery and two others were contract employees from adjacent sites.

The small explosion spewed vapor into the air and led officials to ask residents to remain indoors for several hours. Day said officials do not believe the loading tank fire poses any further threat to the community.

Debris was scattered on the ground below where the tank ruptured in the Manchester area of east Houston, near the Houston Ship Channel. But the cause of the fire is under investigation, Day said. He said the plant is operating at a reduced rate.

The Houston refinery makes gasoline and gas derivatives.