Report: CO 02132019-0543A carbon monoxide alarm was received from a mixed-use building, with retail on the ground floor and residential units above, in downtown Salem. As per protocol, our Central Station operator immediately dispatched firefighters, then alerted building management. Upon arrival, firefighters confirmed elevated levels of the potentially deadly gas in the building. All tenants were evacuated without injury. First responders traced the source of the gas to a small fire in an underground utility vault. The fire was extinguished and repairs initiated.