Why are defective exhaust systems so dangerous? Internal combustion gasoline engines produce extremely high carbon monoxide concentrations. Even a properly tuned gasoline engine, will produce more than 30,000 parts per million (ppm) of CO in the exhaust stream before the catalytic converter. An exhaust leak can allow escape of CO before it is converted to non-toxic CO2 in the catalytic converter. The CO leaking from the exhaust system can enter the vehicle through holes in the body or open windows or doors. Exhaust systems must be gas tight from the engine to the end of the tailpipe.

How does the catalytic converter reduce the risks of CO poisoning? The typical catalytic converter found on most newer cars and trucks combines oxygen with carbon monoxide to form non-poisonous carbon dioxide (CO2) reducing the high concentrations in the exhaust manifold (typically 30,000 ppm or more) to low concentrations (typically below 1,000 ppm after the catalytic converter). Tailpipe concentrations of carbon monoxide in gasoline engines without catalytic converters are typically from 30,000 to over 100,000 ppm, depending on the condition of the engine.

How can CO poisoning occur if the engine has a catalytic converter? Exhaust gas that leaks out before the catalytic converter has high CO concentrations. Out-of-tune or misfiring engines produce elevated concentrations of carbon monoxide and unburned fuel that can destroy the catalytic converter. During cold starts the catalytic converter is ineffective. And if there is insufficient oxygen (caused by operation in a closed building or with a defective oxygen system), there will not be enough oxygen for oxidizing the CO to CO2.

What is the problem with pick-up toppers, open tailgates, and holes in the vehicle body? For carbon monoxide poisoning to occur, a person must breath the CO. Holes allow the CO to enter the vehicle. Every year several people die while sitting in old vehicles with defective exhaust systems and holes rusted through the vehicle floor. When a vehicle is moving, holes or openings in the rear of the vehicle are under a suction which pulls in exhaust fumes. All holes in the car body must be sealed. The suction effect applies when a rear tailgate window or the trunk is left open or when persons ride in the back of a pick-up truck under a topper. The suction produced as the truck is driven and the lack of ventilation in the topper combine to produce a potentially deadly combination. Normally active children who sleep while in the back of a pick-up may be sleepy because they are breathing carbon monoxide. In California, several cases of children dying in the back of pick-ups under a topper have been documented."