The National Transportation Safety Board said Tuesday it is opening a special investigation into Norfolk Southern's safety practices and culture in the wake of a hazardous train derailment in East Palestine, Ohio, and other recent incidents involving the train company.

The last time the agency opened such an investigation was in 2014 for Metro-North following several significant accidents.

The scrutiny comes after a Norfolk Southern freight train carrying hazardous materials derailed on Feb. 3 near East Palestine, Ohio, sending toxic chemicals into the air, soil and creeks in the area. NTSB Chair Jennifer Homendy called the derailment "100% preventable" and said it was "no accident."

Most recently, a Norfolk Southern train derailed Saturday near Springfield, Ohio. The railroad company told authorities that this incident did not involve hazardous materials. But officials acknowledged Monday that cars on the train that did not derail did have hazardous contents.

A Norfolk Southern train conductor was killed in a collision with a dump truck at a rail crossing at the property of steel producer Cleveland-Cliffs, in Cleveland, Ohio, early Tuesday.

Norfolk Southern CEO Alan Shaw is set to testify before the Senate's Environment and Public Works Committee during a hearing on Wednesday.

This is a developing story. Please check back for updates.