Bruce Crummy, Associated Press
FILE - In this Dec. 30, 2013 file photo, a fireball goes up at the site of an oil train derailment in Casselton, N.D. BNSF Railway officials said Friday it appears that a broken rail caused a derailment near the southeastern North Dakota town of Casselton, the second such accident in the past year and the fifth in the area within the last decade.

FARGO, N.D. — BNSF Railway officials said Friday it appears that a broken rail caused a derailment near the southeastern North Dakota town of Casselton, the second such accident in the past year and the fifth in the area within the last decade.

No one was hurt in the derailment around 5:30 p.m. Thursday, which affected 21 cars of an eastbound train carrying lumber and paper and 12 cars of a westbound train carring empty oil tankers. But public officials reacted angrily to what appeared to be Casselton's second escape from a potentially dangerous oil train fire in less than a year.

"I'm not condemning BNSF, but we are owed some answers," Cass County Sheriff Paul Laney said. "To keep having derailments of this magnitude in the same area ... we need to see some research, some studies, whatever it is they do."

BNSF spokeswoman Amy McBeth said the railway is working with the Federal Railroad Administration on factors that led to the break and also plans a broad review of infrastructure in the area.

"The track was visually inspected earlier yesterday with no issues and has been regularly inspected in accord with our track inspection program which complies with federal standards," McBeth said in a statement. "We are grateful that there were no injuries."

The accident comes less than a year after a derailment involving oil tankers 1 mile west of Casselton sparked massive explosions and left a black cloud hanging over the town of about 2,500 people. There were no injuries, but hundreds of people voluntarily evacuated. That accident was blamed on a broken axel.

There were previous derailments around Casselton in September 2009, May 2005 and December 2004.

North Dakota Gov. Jack Dalrymple said BNSF CEO Matt Rose told him Friday the railway plans to do "a complete analysis of every foot" of a roughly 7-mile stretch of track on either side of Casselton and make improvements a priority. That includes the rail base, ballast, ties, crossings and other factors, the governor said.

"The CEO is not satisfied," Dalrymple said. "He's going to make a special project out of that stretch."

Dalrymple was told the lumber train was travelling at 33 mph when it derailed, and the oil tanker train was going about 4 mph. The tankers that derailed were newer models and were not breached, he said.

North Dakota Sens. John Hoeven and Heidi Heitkamp issued statements calling for continued improvements to rail safety.

"As North Dakota grows, we continue to make safety for our communities a priority," Hoeven said. "That is why in the course of our past discussions with BNSF, we have pressed the company to limit speeds where appropriate and make the necessary capital investments to upgrade safety and efficiency."

Said Heitkamp, ""Last night we were lucky. We were lucky the trains that derailed didn't hurt anyone and that the crude oil train was empty. But we can't rely on luck. We saw what happened in Casselton almost a year ago and yesterday's incident is disappointing."