HOUSTON (AP) _ An explosion Saturday at a petrochemical plant destroyed about a third of the facility, killed one worker and injured two others, and rousted about 50 people from their homes, fire officials said.

The explosion and fire occurred about 5:10 a.m. at the three-acre ArChem Co. plant off Interstate 45, Southeast Houston Fire Department Chief David Renfrow said.

''About one-third of the plant was destroyed,'' Renfrow said. ''It took about an hour to get (the flames) extinguished.''

ArChem officials at the scene said they could not provide an explanation for the blast and declined to speak further with reporters. Repeated calls to ArChem's offices went unanswered.

About 50 residents of a nearby trailer park evacuated after the blast were allowed to return home late Saturday morning, Renfrow said. The park was the only residential area near the plant, Renfrow said.

''We thought someone ran into the side of the house,'' said Chris Martinez, who lives near the plant.

''I was sitting here and I heard something go boom and the trailer went rattle,'' said Ed Smith, another evacuee.

The explosion was believed to have occurred in a reactor tank holding toluene, an industrial chemical used as a solvent and in making dyes, Renfrow said.

The 27-year-old worker killed apparently was working on top of the reactor tank when it exploded, said Renfrow. Other tanks also were destroyed.

The two injured workers were taken to Southeast Memorial Hospital, said hospital spokesman Bill McGlashen.

One was in serious condition, suffering from a fractured skull, facial and skin burns and chemical inhalation. The other was in stable condition, suffering from facial and skin burns and chemical inhalation, McGlashen said.