Leaving an oven on could lead to serious health risks and ultimately death. Leaving an electric oven on and unattended can lead to serious burns or a house fire. If a gas oven is left on and unattended, carbon monoxide poisoning can occur, as can serious burns or fire.
Breathing in a moderate amount of carbon monoxide can cause symptoms such as dizziness and nausea, while breathing in high amounts can be fatal. Hundreds of people die from carbon monoxide poisoning every year as the result of leaving a gas stove on for prolonged periods of time. Carbon monoxide is impossible to detect without a special detector because it is odorless.