MADISON, Wis. (AP) — A Wisconsin milling company has agreed to pay an additional $1.8 million in penalties after a corn dust explosion that killed five workers and injured more than a dozen others at its Cambria plant in 2017, the federal Labor Department announced on Thursday.

Didion Milling agreed to the penalties and a long list of safety improvements to settle an Occupational Safety and Health Administration investigation. The settlement comes in addition to a plea deal the company accepted in September in federal court that requires it to pay $10.25 million to the families of victims as well as a $1 million fine.

A federal grand jury indicted Didion last year on nine counts, including falsifying records, fraud and conspiracy. According to court documents, Didion shift employees and supervisors knowingly falsified logbooks inspectors use to determine whether the plant was handling corn dust safely and complying with dust-cleaning rules from 2015 until May 2017.

Corn dust is explosive, and high concentrations are dangerous. Federal regulations require grain mill operators to perform regular cleanings to reduce dust accumulations that could fuel a blast.

Two senior employees were convicted last month of falsifying records and obstructing an investigation into the explosion, and five employees have pleaded guilty and are awaiting sentencing, according to the Labor Department.