A sudden braking caused a train derailment in Harlem, injuring 34 people and causing massive transit disruption. View Full Caption TWU

MANHATTAN — Two track-work supervisors were suspended without pay for not securing a piece of rail that flung an A train off the tracks and into a subway wall, injuring 34 people in West Harlem Tuesday, officials said.

The pair, whose identities weren't immediately released, were responsible for oversight work but failed to secure a piece of replacement rail stored between the tracks, an MTA spokesman said.

They were suspended when their shifts began Wednesday morning at 1:30 a.m., union officials said. They'll go without pay pending both a formal review and the investigation into the crash, MTA officials said.

One supervisor had held his position for about a year after spending six years as a track worker, union officials said. They didn't immediately have further information about the other supervisor.

MTA officials didn't immediately provide details about when they had been working on the site.

On Tuesday morning, a southbound A train hit the replacement rail and "bucked" off the track and into a tunnel wall, jostling terrified passengers from their seats and igniting a track fire that filled the cars with smoke, officials said.

Ultimately, 34 people were treated for injuries that weren't considered life-threatening, officials said.

Storing gear between the tracks isn't abnormal, but crews are supposed to follow particular protocols for securing equipment, officials said. The protocols were not followed in this case, officials said.

"Storing equipment in between tracks is a common practice employed by railroads across the country to accelerate rail repairs," MTA chair Joseph Lhota and Interim Executive Director Ronnie Hakim said in a joint press release.

They reiterated that the derailment was caused by "human error" and not subway infrastructure.

The MTA leaders pledged to survey the entire subway system to ensure track equipment is properly secured.

"Nothing is more important than the safety of our customers. The investigation into this incident continues," they said.

Union officials, however, said it was premature to suspend the supervisors because the investigation is still happening.

"I don't think it's justified. It's an ongoing investigation and already they're pointing the finger at human error. Nobody knows yet," said Michael Carrube, president of the Subway Surface Supervisors Association representing the 4,000 subway supervisors in the city.

"It bothers me that every time something happens to a person or to property, [The MTA] is very fast to point the finger at human error, but as things unwind, it really wasn't human error," Carrube added.

It's not unusual for equipment like spare rails to be stored between the tracks, union officials said.

"That has been going on since before I was born," Carrube said.

Carrube argued that instead of blaming supervisors, MTA officials should allow union officials to help them revamp safety protocols.

"The MTA's policy and procedures for safety need to be revamped. We wait for something to happen before were revamp the system. They need to open themselves up to the union," he said.