Why Does Carbon Monoxide Poisoning Occur When Using Air Conditioning in a Car?

[MacLaila]

Carbon monoxide poisoning from car air conditioning occurs because the tight sealing of car doors and windows makes it difficult for air inside and outside the car to circulate. When the car is stationary but the air conditioning is still running, the carbon monoxide produced by the engine can accumulate inside the car, leading to poisoning and loss of consciousness, and in severe cases, death. Below is an introduction to car air conditioning: 1. Introduction: The car air conditioning system consists of a compressor, condenser, throttle element, evaporator, fan, and necessary control components, designed to regulate the temperature and humidity inside the car, providing a comfortable environment for passengers. 2. Working Principle: When the compressor operates, it sucks in low-temperature, low-pressure gaseous refrigerant from the evaporator. After compression, the temperature and pressure of the refrigerant increase, and it is sent to the condenser. Inside the condenser, the high-temperature, high-pressure gaseous refrigerant transfers heat to the outside air passing through the condenser, causing it to liquefy. The liquid refrigerant then flows through the throttle device, where its temperature and pressure decrease before entering the evaporator.

[MasonFitz]

Once I took a nap at a highway rest area with the AC on and almost had an accident, so I did some research afterwards. When idling with the AC on, the engine keeps running and produces exhaust fumes. If the car is sealed and using recirculated air, carbon monoxide from the exhaust can seep into the cabin through gaps under the car or in the AC vents. This invisible killer binds to hemoglobin more easily than oxygen and can cause confusion in as little as 20 minutes. It's especially dangerous in older cars with poor seals or when parked in a garage. Now I always crack open a window for ventilation when idling with the AC on—safety first.

[AliyahLynn]

The technician explained this principle to me during the last service. The car engine produces carbon monoxide while operating, which is normally carried away by airflow when driving. However, during idling in place, exhaust gases can easily accumulate around the vehicle. If the chassis bushings of an older car are worn out, toxic gases can seep into the cabin through gaps in the chassis. What's even more alarming is that turning on the AC to cool requires activating the compressor, causing the engine to run continuously. Once the recirculation mode is engaged, the cabin essentially becomes a sealed toxic gas chamber. Therefore, it's best to turn off the engine when waiting in summer. If you must use the AC, switch to fresh air mode and open the windows.

[VanCorbin]

During vehicle inspections, I've encountered numerous cases. The exhaust gas emitted from the tailpipe contains 15% carbon monoxide, and the concentration near the vehicle at idle can reach 0.5%. When car windows and doors are closed with the air conditioning on, the intake system may inhale these exhaust gases. The situation worsens in parking garages or tunnels, where lethal concentrations can be reached within five minutes. This is particularly dangerous for models with sunroofs, as hot exhaust gases rise and more easily seep in. It's recommended to open diagonal windows when necessary to create air convection, ensuring more than eight air changes per hour for safety.

[McEzra]

A friend in the emergency department has treated poisoning cases. The poisoning process is like boiling a frog in warm water: initially feeling drowsy and mistaking it for the comfort of the air conditioning, but by the time dizziness and nausea set in, the strength to open the door is already lost. Because carbon monoxide's affinity for hemoglobin is 200 times higher than oxygen, a concentration of 30ppm can cause coma in just two hours. Aging car seals hardening or modified car circuits can increase the risk. I remember once forgetting to turn off the external circulation and sleeping for three hours, waking up with a splitting headache. Now, I turn off the engine if parked for more than 10 minutes.

[CalebLynn]

An automotive engineer shared some data: When idling with the air conditioning on, the engine speed is approximately 700 rpm, and about 240 liters of carbon monoxide are emitted in the exhaust per hour. When the wind speed is below 1 meter per second (such as in underground parking garages), the toxic gas can accumulate beneath the car. The ground clearance of a sedan is only 15 centimeters, making it easy for exhaust fumes to seep back in through floor seams. Passengers in the rear seats are at greater risk because exhaust gas is slightly denser than air. That’s why I never dare to sleep in the car with the air conditioning on when traveling with children.