The National Transportation Safety Board said yesterday that a broken rail caused a fiery train wreck in New Brighton in 2006 and blamed Norfolk Southern for not inspecting or maintaining the tracks properly.

The NTSB ruled that the rail fractured because of an undetected internal defect and said the Federal Railroad Administration also was partly to blame for inadequate oversight of the inspections.

The train, hauling 83 tank cars filled with ethanol from Chicago to New Jersey, derailed on Oct. 20, 2006.

Several cars plunged from a bridge into the Beaver River, where nearly 500,000 gallons of ethanol spilled out, ignited and burned for two days.

No one was hurt, but emergency personnel had to evacuate about 100 people from a seven-block area.

"Because Norfolk Southern did not have an adequate rail inspection and maintenance program, they put the public, crew and environment at risk," said NTSB Chairman Mark V. Rosenker. "Norfolk Southern was not conducting a continuous search of their rail for internal defects, which left segments of rail uninspected and in service indefinitely."

Rudy Husband, the railroad's spokesman, said the company wouldn't comment until it had a chance to review the final report, which won't be available for a few weeks.

The NTSB said the track where the derailment occurred was installed in 1977 and showed significant wear. A contractor hired by the railroad conducted ultrasonic inspections of the track three times in 2006.

The last inspection on Aug. 1 showed an intermittent loss of signal over a 9-foot length of rail in the area where the derailment later occurred. A loss of signal indicates a defect.

The NTSB said Federal Railroad Administration regulations require that all railroads conduct a "continuous" search when inspecting rails for internal defects, so any rail inspection interrupted by loss of signal is not considered valid.

The NTSB said about a year-and-a-half before the accident and without consulting the FRA, the railroad told its inspection contractor that it could ignore a loss of signal as long as it didn't extend beyond five feet of rail.

During the Aug. 1 inspection, the NTSB said, the contractor should have stopped the inspection vehicle to check the rail by hand, as the railroad required.

"This accident illustrates the importance of having a comprehensive rail inspection and maintenance program that will account for factors such as rail head wear and loss of signal during internal testing," Mr. Rosenker said.