(From a Chicago community member)
This past Shabbos morning of Rosh Hashana(the third day of the “three day Yom Tov”) I was awakened by the sound of the carbon monoxide alarm announcing high levels. We immediately cleared everyone out of the house and had the fire department summoned. When they arrived, they informed me that the cause of the high carbon monoxide levels was due to leaving the stove and oven on over Yom Tov and Shabbos. The buildup of these dangerous fumes was not due to a faulty gas line or leaking appliances, but rather to the lack of adequate ventilation.