CHICAGO (AP) — Salvage crews have begun cutting apart and clearing away wreckage from the crash of a Chicago commuter train at O'Hare International Airport's underground station.

Workers wearing face shields have been operating electric saws Wednesday morning, sending sparks flying.

They are cutting apart the lead car of an eight-car train that was damaged during Monday morning's crash, when the train jumped the tracks and barreled to the top of an escalator at the busy airport.

The accident, which happened around 3 a.m., injured more than 30 people.

Union officials say the accident might have begun with the train operator dozing off toward the end of her shift. But federal safety officials say a piece of emergency safety equipment may have also failed.

The National Transit Safety Board is investigating.

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