HOUSTON (AP) _ The captain and two crew members of a Panamanian ship which exploded in the Houston Ship Channel may have caused the blast by illegally dumping hazardous chemicals, federal authorities said.

The fire started May 11 while the 375-foot chemical tanker Seta was moored for repairs at Newpark Shipyard. The 25 crewmen aboard when the Seta exploded jumped into the ship channel.

Federal authorities think residue from chemicals illegally dumped into the ship channel may have been ignited by a spark from a welding torch on an adjacent vessel in dry dock, and the fire spread to the tanker, said Coast Guard Lt. Mary Landry.

Cargo tanks had residue from recent hazardous cargoes of acetone, toluene, caustic soda, mineral spirits, xylene, hexane and kerosene.

The captain and two crew members were arrested Friday.

Goran Bacic, the ship's captain, and Klause Eheler, the port captain, were charged with felony violation of the Clean Water Act, which carries up to a $50,000 fine and three years in prison, officials said.

Doran Prpic, the second-ranking officer, was charged with a misdemeanor violation of the Clean Water Act.

Bacic and Prpic are Yugoslavian, and Eheler is German, officials said. They were released on bond, which was set at $100,000 on the felony charges and $25,000 on the misdemeanor charge, officials said.

The ship channel was closed to regular traffic while firefighters battled the blaze for 12 hours. Three crew members were burned and several firefighters suffered heat stroke.

The Coast Guard, FBI and federal Environmental Protection Agency are conducting a joint investigation, FBI spokesman Charles B. Kearney said.

The fire caused an estimated $2 million in damage, but Ms. Landry said there was little environmental harm.