(Adds company statement, paragraph 3)
By Erwin Seba
HOUSTON, Oct 30 (Reuters) - The U.S. Chemical Safety Board (CSB) said on Wednesday a fuel leak, possibly due to open valves and a running pump, set off a massive blaze at a Mitsui & Co Ltd petrochemical storage operation along the Houston Ship Channel in March.
The fire that began on March 17 at Intercontinental Terminals Co (ITC) spread black smoke across Houston, shut the ship channel, slowed production at local oil refineries and closed roadways and schools as it spread from one giant storage tank to 10 others before being extinguished on March 20.
"ITC has been cooperating with the CSB and other federal, state and local regulatory authorities in their respective investigations of the March fire at the Deer Park facility," said a company spokesman. "These investigations continue, and ITC is working with the government agencies to identify potential causes and take appropriate steps to ensure safe operation."
The safety board said investigators believe the fire started in piping next to a 80,000-barrel tank containing naphtha, a flammable liquid used in motor fuel production.
A pump connected to the piping was left running for several hours beginning the night before to mix the naphtha with another fuel and prepare it for export on March 17, it said.
The board's lead investigator noted that valves on the piping had to be operated manually, preventing emergency workers from being able to shut the piping system as the fire spread.
"The leaks could not be controlled once the fire started," said CSB lead investigator Crystal Thomas in a presentation on Wednesday.
The safety board plans to pursue the piping and other possible ignition sources for the blaze. Its review could answer "why the fuel release was not detected before ignition, why the release was not isolated, and why prolonged emergency response efforts were necessary to control and ultimately extinguish the fire," according to an initial report released on Wednesday.
No injuries were reported from fire.
The CSB investigates chemical plant explosions and fires to determine root causes to improve plant safety, but has no regulatory or enforcement power.
Mitsui faces criminal charges for spilling chemicals into waterways around the ITC terminal in the Houston suburb of Deer Park, Texas, after the fire was put out.
Vopak, which operates a storage terminal adjacent to ITC, sued in May for at least $1 million in lost business and damages.
Reporting by Erwin Seba Editing by Jonathan Oatis and Tom Brown