How long can you sleep in a car with the windows closed before experiencing oxygen deprivation?

[LeAaliyah]

Sleeping in a car with the windows closed will not cause oxygen deprivation, as the vehicle is not an airtight space. Significant damage to the car's engine: Sleeping for extended periods with the air conditioning on while the car is stationary can have a major impact on the engine. Since the engine is running to provide power but the car is not moving, this increases the rate of carbon buildup in the engine and also raises fuel consumption. Can lead to increased fatigue: Sleeping in the car, due to the lack of proper seats and back support, often results in back and muscle pain during rest. Maintaining one position for a long time, especially when leaning against the seat, tends to concentrate pressure on the lower back. This sleeping posture further strains the back, leading to a feeling of increased fatigue rather than restfulness.

[Bella]

A few days ago, my buddy almost got into trouble. He was so exhausted from a long drive that he rolled up the windows and took a nap at a rest area—just 40 minutes. When he woke up, he felt dizzy, nauseous, and broke out in cold sweats. This is something we really need to take seriously. Sleeping with the windows completely closed is extremely dangerous. We consume oxygen when we breathe, and the car's interior is so small that it can lead to oxygen deprivation to the point of unconsciousness in just two or three hours. It’s even scarier in winter—haven’t you heard those news stories about people who turned on the heater to sleep and ended up with carbon monoxide poisoning? If you really need to rest, I suggest cracking a window slightly or tilting the sunroof at an angle for safety, and it’s best not to sleep for more than half an hour. By the way, the security guard at the rest area mentioned they often see drivers waking up with their faces purple—seriously, don’t gamble with your life.

[ElliotDella]

Last time I couldn't handle night driving and ended up sleeping in the car with windows closed. It got stuffier by the minute, and my heart was pounding uncomfortably. I did the math - a regular sedan only has about 3-4 cubic meters of air. With two people sleeping, oxygen depletes fast. My cousin in the ER mentioned treating patients who suffered oxygen deprivation from sleeping in cars, with CO2 levels 4-5 times above safe limits. Now I know better: always open diagonal windows when resting, or bring window guards that keep them slightly open. And don't assume AC's external circulation is safe - what if leaves block the intake? Bottom line: maintain airflow when resting in vehicles.

[DeFaith]

I get especially nervous when my child falls asleep in the car. Kids have fast metabolisms—just 20 minutes with the windows closed can drop oxygen levels below 18% (normal is 21%). Infants in car seats are particularly at risk, as tilting their heads forward can make breathing even harder. I did a test with an air quality monitor: after 40 minutes with the engine off and windows closed, PM2.5 levels stayed the same, but CO2 skyrocketed to 4,000 ppm—10 times outdoor levels! Families with babies must be vigilant. Never leave a child alone in a closed car, even briefly for errands like quick AC stops. Last year, there was a tragic case of child suffocation.