OMAHA, Neb. • Federal investigators announced on Tuesday a special investigation into rail operator Norfolk Southern after a fiery derailment on the Ohio-Pennsylvania border in February and several other accidents, including the death of a train conductor just hours earlier Tuesday.

The National Transportation Safety Board said it will begin a broad look at the railroad’s safety culture, saying it has sent investigation teams to look into five significant accidents involving Norfolk Southern since December 2021.

The agency also said it was urging the company to take immediate action to review and assess its safety practices.

It announced plans Monday to improve the use of detectors placed along railroad tracks to spot overheating bearings and other problems in response to the derailment in Ohio last month.

NTSB has said the crew operating the train that derailed Feb. 3 outside East Palestine, Ohio, got a warning from such a detector but couldn’t stop the train before more than three dozen cars came off the tracks and caught fire.

Half of the town of about 5,000 people had to evacuate for days when responders intentionally burned toxic chemicals in some of the derailed cars to prevent an uncontrolled explosion, leaving residents with lingering health concerns. Government officials say tests haven’t found dangerous levels of chemicals in the air or water in the area.

Within the industry, Norfolk Southern has had a strong reputation for being a safe railroad over the years, said Christopher Barkan, director of the Rail Transportation and Engineering Center at the University of Illinois.

But pressure has been mounting on the railroad in the aftermath of the East Palestine derailment.