How Long Can the Oxygen in a Sealed Car Last for Breathing?

[Pearl]

The oxygen in a sealed car can last for about 8 hours. Oxygen needed for a night's sleep: One person requires approximately 96 liters of oxygen for 8 hours of sleep. Oxygen available in the car: The actual usable oxygen inside the car is only about 105 liters. Self-rescue methods in a sealed car: Usually located on the right side of the rear part of the car, this small hole is often hidden and is referred to as an emergency hole. Human oxygen requirements: Each breath a person takes is about 500 milliliters of air. Based on 16 breaths per minute, each person requires about 12 cubic meters of air per day. Approximately 22.6 liters of carbon dioxide are exhaled per hour. Normally, oxygen makes up 21% of the air. When the oxygen content in the air drops to 12%, breathing difficulties can occur; at 10%, cognitive functions may decline; and below 7% to 8%, it can be life-threatening. Roughly, each person needs about 0.5 cubic meters of air per hour. An adult requires about 500 liters of oxygen per day, averaging 21 liters per hour.

[McLondyn]

I was just chatting with a friend and this came to mind—if a car is completely sealed, we really need to carefully calculate how long the oxygen inside would last. A typical sedan has an interior space of about 3 to 4 cubic meters, with oxygen making up roughly 21% of the air. A person sitting still consumes approximately 0.3 liters of oxygen per minute. Assuming it's just me in the car and the air volume is around 3.5 cubic meters, the total oxygen would be about 700 liters. Doing the math, theoretically, it could last around 4 hours. But in reality, the bigger danger is the buildup of carbon dioxide, which can reach toxic levels within an hour, causing headaches and difficulty breathing. Don’t assume you’re safe until the oxygen runs out. I’ve also looked up experimental data—even tiny gaps in a car can allow air to slowly seep in, so never sleep in a sealed car or conduct airtight experiments. Safety first: crack a window or turn on the AC for ventilation. Regularly check the door seals to prevent problems before they arise.

[AlexaDella]

Once when I went camping, I accidentally got locked inside the car for a few minutes, and it felt really uncomfortable—I could hardly breathe. At that moment, I wondered: how long would the oxygen last if the car were completely sealed? A small car holds about 4,000 liters of air, with at least 800 liters of oxygen. However, a person at rest consumes roughly 0.25 to 0.35 liters of oxygen per minute. A rough estimate suggests you could last 3 to 5 hours. But carbon dioxide levels rise much faster, becoming dangerous within half an hour, causing dizziness. After this experience, I understood why seasoned drivers often warn against sleeping alone in a locked car, especially with children. A car isn’t an airtight tank—wind can push air through gaps. Don’t take the risk. Remember, if you’re ever stuck, immediately open a window or honk the horn for help.

[StHector]

This question is often asked, and the answer is that the oxygen inside the car is generally enough for an adult to last 2 to 4 hours, but don't assume that the duration is long and there's no urgency. Once the car is sealed, carbon dioxide levels can rise to harmful levels within half an hour, before the oxygen runs out. I've seen cases where a car owner was trapped in a garage for several hours and ended up unharmed but shaken. The simple rule is: don't test it unnecessarily, ventilate as soon as possible. The car's small volume means limited air supply—safety is more important than curiosity.