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Last Updated On October 31, 2020

Can You Sleep in a Car with the Windows Closed?

Cars are comfortable machines, and no one would blame you for attempting to sleep in one. They have soft chairs that can recline, a roof to protect you from the elements, and an air conditioning system that will keep you as hot or cold as you like.

Sleeping in a car is all its cracked up to be

The notion of sleeping in a car with the windows closed sounds foolish. Some people are convinced that such a situation would end in suffocation. But they are wrong:

First of all, some people prefer to close their car windows when they sleep because it is safer. Leaving your car windows open while you sleep, especially at night, leaves you vulnerable to attack.

You will run out of room before you run out of air

Secondly, people are convinced that sleeping in a car with the windows closed will lead to suffocation because they think that cars are airtight. However, that is not true. Cars are not watertight either. They are merely water-resistant.

A car has rubber seals around the doors, but they are designed to protect the interior cabin from conventional weather elements like rain. If you submerge a vehicle, it will eventually sink. The door seals will probably remain in place, but the water can still penetrate the car via openings like the vents that constitute the ventilation system.

When you close the windows, these same vents will continue to carry air in and out of the car. Even when your AC system is off, air continues to circulate within the interior cabin.

Harvard studied air flow in cars

Some people are probably tempted to dismiss the claim above as a theory, but it is based on scientific evidence. Havard University Environmental Health Researchers performed an experiment in 1998 designed to determine the amount of air that circulates through a vehicle’s interior cabin when the windows are closed.

They found that the air within a parked car (whose windows were closed) was replaced every one to three hours. In other words, you have no reason to worry about suffocation.

Is it completely impossible to suffocate in a car with closed windows?

It is a question of numbers. The car has plenty of oxygen for one person. But the more people you have in the car, the more oxygen they consume. The average car would have to contain more than nine people for the oxygen levels to fall below the safe threshold.

Should you sleep in a car with the windows down?

It depends on the location. The practice is healthier because it gives you access to more fresh air. But you should never roll the windows all the way down. Do not leave room for an intruder to push his way into your vehicle.

Is carbon monoxide poisoning possible?

Carbon monoxide poisoning is a more significant concern than suffocation where cars are concerned. The fumes a vehicle produces are highly toxic, and inhaling them in substantial quantities will either ruin your health or kill you.

That being said, carbon monoxide poisoning is only a problem for people that permit their engine to run while they sleep. This threat is even more pronounced for people whose vehicles are parked in enclosed spaces. If you have sufficient ventilation and the engine is off, carbon monoxide poisoning isn’t possible.

How can you avoid carbon monoxide poisoning?

Most people keep the engine running because they want to either cool or heat the interior of their car while they sleep. The easiest way to prevent carbon monoxide poisoning is to keep the engine off.

If you want to manipulate the temperature, turn the engine on long enough to either raise or lower the heat to a satisfactory level. Once you are comfortable, switch the engine off and go to sleep.

You are discouraged from falling asleep with the engine on. As was noted above, enclosed spaces are dangerous. Keep your car in the open. You should also avoid parking near other cars whose engines are running.

Carry out regular maintenance. Look for signs of a faulty exhaust system. Even if you trust the health of your vehicle, consider buying a carbon monoxide detector. It will put your mind at ease.

Where is the best place to park your car before you sleep?

Carbon monoxide poisoning isn’t your only concern. Whenever you fall asleep in a vehicle, even when the windows are closed, you leave yourself vulnerable to criminal elements. One way of avoiding trouble is to look for designated rest areas (DRA’s).

DRA’s are generally littered with other vehicle owners sleeping in their cars. This offers a sense of security. If you cannot find a designated rest area, look for a well-lit location that provides the most significant visibility.

Try to park in a way that places the driver’s door against a solid object such as a tree or a wall. This will prevent an intruder from immediately taking you out once they breach your vehicle. It also gives you a few moments to react once the intruder breaks the window on the passenger’s side. This assumes that you locked the doors and rolled up the windows.

Is heat a serious threat?

It is more comfortable to sleep in a car in cold weather than it is in hot weather. Hot weather complicates things because you cannot roll your windows all the way up. You run the risk of overheating. This can lead to exhaustion and even death.

Some seasons are so hot that cracking the window open isn’t enough. If you want to keep the windows closed but don’t want to depend on your air conditioning, buy a portable fan. You should also make use of your windshield reflector.

If you have a moonroof (or as we call it in Australia, a sun-roof), you don’t have as much to worry about. Otherwise, remain hydrated. The simple act of drinking water will keep your body cool.

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How do you stay warm in a car?

While the heat is more dangerous, some winters are so harsh that they can make sleeping in a car a nightmare. You might be tempted to roll the windows all the way up. But that isn’t a good idea because the difference in temperature between your body and the air in the car will ultimately produce moisture that will complicate your attempts to stay warm.

You can prevent this from happening by cracking the window slightly. Be sure to wear your warmest layers of clothing. Wrap yourself in a blanket if your clothes have failed to keep the cold out. Better yet, buy a sleeping bag. It will keep you warm and toasty on a cold night.

Most people would rather sleep in a warm bed. But if circumstances force you to spend a night in your vehicle, you should take comfort in the fact that it is perfectly safe to sleep in a car with the windows closed.

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