Its burning emits high carbon monoxide levels. Wood burning can also be hazardous if the fireplace flue is not clear, or if a wood burning stove is not vented. Gas ovens or ranges should never be used to heat a room. During winter, many residents insulate windows and doors to prevent drafts. Prolonged use of a gas oven or portable heater in an insulated area will diminish the supply of oxygen and generate carbon monoxide that can reach lethal levels.
Fresh air is the quickest antidote to carbon monoxide poisoning.
But if you even suspect carbon monoxide poisoning, seek appropriate medical care and have your home's heating and fuel-burning systems inspected by a trained professional.