Plant officials began work on a new utility shaft and planned to restart a major ventilation fan after available underground air became restricted following an accidental radiological release in 2014 that contaminated parts of the mine, the Carlsbad Current-Argus reported Saturday.

Over the weekend, officials moved forward with a multimillion-dollar project to rebuild the ventilation system known as the Safety Significant Confinement Ventilation System. It is expected to provide 540,000 cubic feet (15,300 cubic meters) per minute of breathable air to underground workers when it is expected to be completed in 2025.

Carlsbad Nuclear Task Force Chair John Heaton said the group is working on multiple projects in the meantime to enhance workforce safety related to airflow, including converting all vehicles to electric.

“The main importance of it is worker safety. Running diesel creates many toxic fumes in the enclosed area,” Heaton said. “There’s a big major effort to go to all electrically run equipment so that there’s no diesel.”

Department officials said the underground fleet includes 80 vehicles, with 37 considered essential to the plant’s operations. Officials said it could take about five years to replace or convert all 37 diesel vehicles.

Officials are also considering battery-electric vehicles that would run with zero emissions, and have already replaced the engines in some older diesel vehicles to reduce emissions.

Heaton said reducing diesel equipment could cut down on risks like fires or environmental contamination.

“There’s a significant amount of diesel fuel that has to be held underground in storage for vehicles that are still diesel. That represents a risk itself,” he said. “They’ve moved very quickly in purchasing the low emission vehicles. They want to replace everything underground and make it all run on electricity.”