PNM Resources Inc. is continuing to investigate a fire that occurred on March 17 at its San Juan Generating Station near Farmington, N.M., that caused the plant's smallest generating unit to be taken offline.

A structural failure of a coal silo for San Juan unit 1 caused a fire that resulted in some damage around the silo as well, PNM spokesman Dan Ware said on March 20. The silo is where coal is dumped before it is milled into powder for combustion to power a steam turbine.

No information was immediately available on when the 340-MW plant, which is more than 40 years old, will be returned to service. Ware said damage and repair needs are still being assessed for the unit's silo and surrounding area.

"The cause is under investigation," Ware said. "Unit 1 will remain offline until all assessments and repairs are complete."

PNM closed San Juan units 2 and 3 in late 2017, but has continued to operate units 1 and 4. PNM owns more than 66% of the 847-MW plant and is the facility's operator. Unit 4 is 507 MW.

"Unit 4 is operating normally and this incident has not affected our ability to serve our customers," Ware said.

While San Juan County and Farmington fire departments responded to the 5:47 p.m. incident, no injuries were reported and no fire suppression was needed, the county said.

PNM plans to fully close the plant in mid-2022 when coal supply and ownership restructuring agreements with the plant's other partial owners expire.