Very few people today successfully commit suicide by carbon monoxide leaving a car running in a closed garage. Cars under normal circumstances don’t produce much carbon monoxide. Intentional carbon monoxide poisoning is difficult on modern cars. But tragic accidents still kill people who leave cars running in garages. How so?

A properly running automobile uses oxygen to burn gasoline to produce power. The tailpipe releases a non-toxic to humans gas – carbon dioxide. Not to dangerous if you have a sufficient oxygen supply. The same car left running for a number of hours in a closed garage will consume two parts oxygen for every part carbon in the gasoline. Eventually oxygen levels will fall to a point where a human will start to asphyxiate should they enter the garage.

At the same time the car engine will start to asphyxiate from a lack of oxygen. The oxygen sensor in the car will throw an error code and check engine light will come on. However the engine will keep running in a limp home mode but incredibly rich. The rich fuel mixture will stop the catalytic converter from properly working and will cause the engine to burn rich producing carbon monoxide at levels much higher than usual. Until all the oxygen or fuel is gone, the engine will produce incredible amounts of deadly carbon monoxide.

Between asphyxiation from a lack of oxygen and carbon monoxide produced by the oxygen starved car engine, you have a deadly mix – even on cleanest, most modern car that when driven on the street produces little of the deadly carbon monoxide poison.