Federal investigators say they know what caused a runaway freight train in Yakima last year that derailed four tank cars containing thousands of gallons of liquefied propane: Nobody set the brakes.

"It was apparent (to investigators) that not all the hand brakes had been had been properly applied," said Warren Flatau, a spokesman for the Federal Railroad Administration in Washington D.C.

The derailment occurred a year ago -- on April 8, 2007 -- when an unmanned 37-car Burlington Northern Santa Fe train with two locomotives plowed off a sidetrack alongside the S.S. Steiner hops warehouse on Washington Avenue.

The train was going backward, derailing four propane tank cars at the tail of the train. The crash temporarily forced the evacuation of the nearby Yakima County Sheriff's Office, but the double-hulled tank cars withstood the impact and no propane escaped.

Flatau said investigators determined the accident was caused by human error. Those findings were based on a combination of interviews with BNSF personnel and an analysis of something called "locomotive event recorders."

"Human factors are the leading cause" of train accidents, Flatau said, adding that most derailments are caused by track or equipment malfunctions.

He said his agency determined that two BNSF employees, a conductor and a brakeman, played a role in the accident. He declined to release their names, citing federal privacy laws, and said his agency was not a party to BNSF disciplinary matters.

He said his agency has proposed two civil penalties of up to $5,000. The case remains active, he said, adding that agency officials and the railroad are currently "negotiating a settlement."

Gus Melonas, a spokes-man for BNSF in Seattle, declined to comment. Shortly after the accident occurred, Melonas ruled out vandalism or sabatoge as a cause.

The sequence that led to the derailment began about 4 p.m. on a Sunday afternoon when the train started rolling backward on a visually imperceptible grade of 1 percent from the railroad yard near Nob Hill Boulevard.

Nobody apparently noticed what was happen-ing. On its journey the train passed through the grade crossing on Mead Avenue, automatically triggering the crossing guards. Police said they think motorists who waited out the slow-moving train -- it probably never exceeded 10 mph -- didn't realize it was unmanned.

The train ran out of track next to the Steiner warehouse, derailing the tank cars -- each containing approximately 33,000 gallons of liquefied propane -- and causing massive damage to a short stretch of the spur.

After an initial evac-uation of the immediate vicinity, local officials determined the propane cars were not leaking and called off a hazardous materials mobilization.

A Steiner employee said BNSF quickly paid for repairs to the warehouse. The employee, who spoke on the condition his name would not be used, said Steiner was not otherwise financially harmed because BNSF owns the property where the Steiner warehouse sits and the track that was damaged.

The accident occurred a month after a derailed CSX Corp. train carrying liquefied propane touched off an explosion in Oneida, N.Y., that forced evacuations for miles around, including parts of the city's downtown.

It was unclear from news reports if the cause of that crash has been determined. Investigators at that time predicted the case could take up to 18 months to resolve.

* Chris Bristol can be reached at 577-7748 or cbristol@yakimaherald.com.