Passengers were evacuated from an F train that derailed in Woodside, Queens on May 2, 2014. View Full Caption Metropolitan Transportation Authority / Patrick Cashin

WOODSIDE — A broken section of rail discovered at the scene of the F train derailment in Queens earlier this month was inspected just a week before the incident and found to have no issues, an MTA spokesman said.

The rail had been checked by both an inspector who was on foot and a specialized rail car that can detect internal defects a week prior to the May 2 incident, when a Manhattan-bound F train derailed in Woodside, injuring 19 people and forcing hundreds to evacuate from a smoky tunnel.

Investigators were still trying to determine the official cause of the derailment. It was also not clear what caused the rail to break.

"This investigation is still very fluid. It's still ongoing," NYC Transit President Carmen Bianco said at the MTA's transit committee meeting on Monday. The state's Public Transportation Safety Board is also involved in the probe, he said.

Investigators are conducting a forensic analysis of the broken rail, according to Bianco, as well as testing others that came in the same shipment.

"We have identified many of those rails, a good percentage, and we are performing analysis on those rails also," he said.

No issues have been found with the other rails that have been identified in that batch so far, according to an MTA spokesman.

The rail that broke was installed in February after a hairline crack was discovered in the rail that was previously installed at that location, according to the MTA. It was shipped from the manufacturer in December.

Pennsylvania-based ArcelorMittal Steelton, which made the rail, has been supplying steel rails to the MTA for almost a century, a spokesman said in a statement.

ArcelorMittal's rails undergo ultrasonic testing and a visual inspection before leaving its facility and are "designed to last for decades," according to the statement. The rail involved passed a final inspection on Nov. 25 before being shipped on Dec. 3, the company said.

In a statement, ArcelorMittal's spokesman said "it's too early to speculate on what caused the rail to fracture."

The company is cooperating with the MTA in its investigation, he said.