Federal agencies are now investigating a fatal gas leak at a Baileyville paper mill last month that killed a 20-year-old man and injured nine other workers.

The U.S. Chemical Safety and Hazard Investigation Board (CSB) says it’s looking into the company’s chemical handling practices, safety systems, and emergency response actions.

The gas leak at the Woodland Pulp, LLC facility resulted in the death of Kasie Malcolm, a student at the University of Maine who was an intern at the paper mill.

One of the nine other injured people remains hospitalized.

According to CSB, the incident may have involved the mixing of concentrated sulfuric acid with sulfurous compounds in an enclosed process sewer. The agency says the mixing could have resulted in the generation and release of hydrogen sulfide, a highly toxic gas, in the Bleach Plant area of the facility.

A team of CSB investigators already has been deployed to the incident scene.

The Press Herald reports the Occupational Health and Safety Administration has also initiated its own investigation into the incident.

The CSB does not issue citations or fines but makes safety recommendations.