Brookfield Volunteer Fire Company is warning of the dangers of carbon monoxide poisoning.  Yesterday, while on a follow up inspection, the Deputy Fire Marshal found a commercial occupancy with elevated CO levels due to an improperly vented portable heater. There were 3 occupants who requested medical evaluation. The building was ventilated and the heater removed. The occupants all refused treatment by EMS.  Fire officials are reminding everyone to assure all heating devices are properly ventilated and that working CO detectors are installed in homes and businesses.