The National Transportation Safety Board opened a "special investigation" into Norfolk Southern Railway's safety practices and culture on Tuesday afternoon.

In a press release, the NTSB noted five "significant accidents" that have been investigated by the agency involving Norfolk Southern since December 2021, including the toxic freight train derailment in East Palestine, Ohio, on Feb. 3. The derailment caused hazardous chemicals to spill onto the ground and sent a plume of smoke into the air. 

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Ohio train derailment smoke

This photo taken with a drone shows portions of a Norfolk Southern freight train that derailed Friday night in East Palestine, Ohio are still on fire at mid-day Saturday, Feb. 4, 2023.  (AP Photo/Gene J. Puskar)

"Given the number and significance of recent Norfolk Southern accidents, the NTSB also urges the company to take immediate action today to review and assess its safety practices, with the input of employees and others, and implement necessary changes to improve safety," the NTSB statement reads.