(Corrects gallon to barrel in paragraphs 3 and 12)
HOUSTON, Oct 30 (Reuters) - The U.S. Chemical Safety Board (CSB) said on Wednesday that leaking volatile naphtha, possibly due to open valves and a running pump, set off a massive fire at Mitsui & Co Ltd's Intercontinental Terminals Co (ITC) operation along the Houston Ship Channel in March.
The fire that began on March 17 spread a black cloud of smoke across Houston, shut the ship channel, led to cuts in production at nearby refineries, closed roadways and school districts as it spread from one giant storage tank to 10 more before being put out on March 20.
The board said the fire began in piping next to a 80,000-barrel tank containing naphtha. A pump connected to the piping was left on for several hours beginning the night before to mix butane with the naphtha.
The board noted that valves on the piping had to be operated manually, increasing risk in an emergency.
"Under a major fire scenario resulting from a leak near this equipment, neither ITC operators nor emergency responders could access the area to close these manually operated valves," the CSB said.
In addition to further examining piping that was the source of the naphtha leak, "the CSB plans to identify potential naphtha release points and ignition sources, determine 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."
No injuries were reported from the breakout of the blaze to when it was extinguished.
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. The company was cited by the U.S. Occupational Safety and Health Administration for violations following the fire.
Vopak, which operates a storage terminal adjacent to ITC, sued in May for at least $1 million in lost business and damages. It alleged the ITC's negligence and inability to quickly stop the fire shut Vopak’s operations for weeks.
There are also 23 other personal injury claims filed against ITC, according to court records.
The fire began on March 17 in a 80,000-barrel storage tank located in the middle of 15 similar size storage tanks, the CSB said. (Reporting by Erwin Seba Editing by Chizu Nomiyama)