UPDATE: NTSB Investigators Unraveling Cause Of Fiery Caltrain Collision That Injured 13

SAN BRUNO (CBS SF) -- Federal investigators meticulously combed through debris Saturday in the wake of a fiery crash between a Caltrain engine and construction equipment that injured 13 people and has shut down rail service between the South San Francisco and Millbrae stations.

A team of six National Transportation Safety Board investigators arrived at the scene Friday morning to begin the probe into the collision. Caltrain has said they will not remove the damaged train or begin repairs to the track until the NTSB has given the all-clear.

"From where the train hit and the vehicles came to rest was over 500 feet so they hit pretty hard," said National Transportation Safety Board Vice Chairman Bruce Lansberg. "One of the vehicles had it's fuel tank punctured and that was the source of the fire. The fire did not initiate from the locomotive itself."

Lansberg told reporters among the investigative tools the NTSB will be using will include video from a camera on the engine.

"This is going to be tremendously helpful to us as we established what happened in this crash," he said.

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The investigative team plans to be at the collision site for several days in order to collect all of the perishable evidence related to the crash. Additional data collection of about three months will be followed by a period of analysis likely to take 15-18 months before a final report on the incident is issued.

The track closure in the area was continuing to impact commuters on the Peninsula. The system only had 69 trains in service as opposed to its usual 104 trains.

Caltrain rider Worthington Foster found out about the collision and the delays it was causing when he got on Caltrain Friday morning. Samtrans buses were taking passengers between the South San Francisco and Millbrae stations, causing some delays.

"It would have been nice to know ahead of time that I would have this extra stop," said Foster.

"Got here, didn't know what was going on. Someone told me about it, so I was like, 'Oh, OK,'" said Andrea Xu, another Caltrain rider. "It's just kind of confusing and kind of hectic."

The bus bridge will be in place until at least 4 p.m. Friday. For the rest of the system, Caltrain will continue to operate under its regular weekday schedule. Passengers traveling between the South San Francisco and Millbrae train stations should expect service delays as a result of the bus bridge.

Passengers can also find other public transportation options by visiting 511.org.

Caltrain officials said the equipment involved in the collision was part of the system's ongoing electrification project, but it should not have been on the tracks as the commuter train with 75 passengers aboard approached.

"All the equipment should have been cleared of the tracks when trains come through," said Caltrain spokesperson Dan Lieberman. "We've been doing construction on the tracks throughout electrification. That's under investigation."

Neighbors who live near the crash site told KPIX 5 it was not uncommon to see workers near the tracks.

"These guys are working on this whole line every day," said area resident Larry Valencia. "I know they're super safety conscious and all of that, but why was that train flying on that track where the truck was?"

That will be among the many questions federal investigators will be trying to answer.

"There are watchmen on site that are communicating with dispatch, but ultimately, it's not clear where the breakdown took place," Lieberman said. "This is not exactly a happy day, but we're glad it is not worse than it is."

Caltrain officials said a total of 13 people were injured in the collision, but none of the injuries appeared to be life-threatening. San Bruno Fire officials said that five of those injured, including two Caltrain employees, individuals were transported to area hospitals.

"Our deepest thoughts and sympathies are with all those who were injured today," said Caltrain's acting executive director Michelle Bouchard in a statement issued by the agency.

Early Friday morning, commuters riding on the rail line between San Jose and San Francisco were forced to use a bus bridge between the South San Francisco and Millbrae stations. SamTrans and BART were also providing mutual aid.

The collision near Scott Street in San Bruno happened around 10:38 a.m. when the train slammed into two pieces of equipment on the track.

The force of the impact ripped the equipment apart, with the burning cab remaining in front of the engine and another large piece of wreckage coming to rest several cars back. Burning gasoline could be seen under several cars.

Passengers told KPIX about the terrifying moments that followed.

"It was pretty chaotic. There was maybe 15 seconds where nobody knew what to do," Jesse Miller told KPIX 5. "Some people started opening up the emergency exits in the windows. Some people actually jumped out of the windows."

Miller posted an image on Twitter of the fireball moments after the crash.

"I saw one worker who was taken away in an ambulance. He looked like he got some cuts and serious bruises," said Caltrain passenger Elizabeth Tom. "I saw another passenger, he had a gash on his eye."

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