The United States transportation regulator issued a special investigation into the Norfolk Southern Railway’s safety recorda month after one of his trains derailed and release toxic chemicals in a city in the state of Ohio.

The National Transportation Safety Board (NTSB) announced the investigation after an employee was killed in a work-related accident on Tuesday — the third such incident since late 2021.

The NTSB said it’s the safety culture of the organization“given the significant number of recent accidents in Norfolk Southern.”

Ohio accident: what are the health risks of the chemicals released after the train derailment in eastern Palestine

He pointed to five serious accidents: the three work-related deaths since December 2021 and two derailments this year.

The company has been criticized for the Feb. 3 derailment of a freight train in East Palestine, Ohio spilled hazardous materialincluding the carcinogenic chemical vinyl chloride.

The accident started a fire that spread dangerous smoke and gases into the community.

Authorities were forced to send the controlled release of vinyl chloride to prevent a possible explosion.

Critics have said the accident was preventable and called for an investigation by the company, which has more than 18,000 employees and 30,000 kilometers of track.

Another Norfolk Southern ten derailed on March 4 near Springfield, Ohio.

“NTBS is concerned that many organizational factors may be involved in accidents, including safety culture,” it said in a statement.

Norfolk Southern CEO Alan Shaw said in a statement that the cause of Tuesday’s crash is still unknown, but that the company will “fully cooperate” with the NTSB.

He said he has stressed “the urgency of finding new solutions” to security issues to senior officials.