A freight train derailment Tuesday in the City of Industry sent 21 railcars into a tangled heap, spilled flammable liquid and disrupted Metrolink service.
About a dozen businesses were evacuated after the 9:30 a.m. crash of the Union Pacific train near Fullerton Road and Railroad Street.
Officials said the cause was under investigation but that there was no indication of an obstruction on the tracks.
No one was injured.
"We were very fortunate," said Los Angeles County Fire Department spokesman Ed Osorio. "The train and the cars did not hit anything else."
Three tankers on the 48-car westbound freight train contained combustible propylene glycol, used to make antifreeze. Liquid poured from one overturned car, which had been punctured.
Firefighters evacuated 150 to 200 people from a commercial strip that included an office building, fast-food restaurant and retail shops, in case of an explosion or fire. The evacuation ended four hours later.
The same businesses were briefly evacuated again later when workers feared a crane righting the cars had punctured a natural gas line. It had not.
Investigators from the Federal Railroad Administration were searching the scene late Tuesday for clues to the cause of the derailment.
The speed limit is 65 mph on that section of track, but it was unknown how fast the train was going, said Mike Furtney, a Union Pacific spokesman at the scene.
Osorio said fire officials spoke to the engineer, who was mystified about the cause of the derailment.
"He said there was nothing wrong with the train, and he didn't see anything that he hit."
The locomotive did not derail. Furtney said the middle cars may have derailed because of a track or equipment problem.
Metrolink service on the Riverside line, which shares the tracks with Union Pacific, will remain canceled today, spokeswoman Denise Tyrrell said.
Airborne danger was ruled out early on, officials said. "These cars are placarded and identified with what they're carrying," said county fire Inspector Ron Haralson.
Union Pacific official John Bromley said no other hazardous materials were on the train, which also carried paper products and a load of plastic pellets. "There was no danger to the public," he said.