EL PASO, Texas (KTSM) – Las Cruces firefighters responded to a report of a possible fire at Vista Middle School just after 9 a.m. Monday, Sept. 12.

Firefighters found a classroom containing what they called a “moderate” amount of smoke.

The building had already been evacuated by the time firefighters arrived. The source was a malfunctioning heating/air conditioning/ventilation unit, fire officials said.

Fire crews ventilated the building and within an hour, the building was determined to be safe for students and staff to return and resume their day.