So, is it Safe to Sleep in a Car with the Windows Closed?

Whether you are waiting for rescue or you just need to take a break from long, boring hours of driving, most of us have probably had cause to get a little sleep in our vehicles before.

car interior

Wherever you might be, reclining the driver’s seat or stretching out across the backseat to grab a few winks with the windows closed and the doors locked is definitely appealing.

However, many of us have likewise probably heard advice to the contrary, a warning that we should never sleep in our car with the windows closed.

So, is it safe to sleep in your vehicle with the windows rolled up or not?

No, never sleep in your vehicle with the windows closed tightly. A running engine might lead to carbon monoxide gas building up in the cabin, potentially poisoning you and other occupants.

Now, you have probably done this before with no ill effects. I know I have.

Whether I’m battling cold weather or hot weather, keeping your vehicle sealed up with the air conditioner or heater running while you grab a cat nap seems like a great idea.

Unfortunately, in some circumstances this can indeed prove to be fatal.

I’ll tell you more about the hazards of carbon monoxide gas, and all the other variables that you’ll need to know in order to make a good decision on the subject below.

Sleeping in a Car with the Engine Running Might Expose You to Carbon Monoxide

The bottom line is that sleeping in a car or any other vehicle that has the engine running and the windows rolled up tightly can expose you to carbon monoxide gas.

Although unlikely, this gas is not easily detected and is particularly dangerous when you are already asleep or otherwise unconscious.

CO Gas Buildup is Extremely Dangerous

You probably already know that a running internal combustion engine emits exhaust fumes.

These exhaust fumes contain all sorts of chemicals and elements created as a byproduct of combustion, and one of them is carbon monoxide, or CO, gas.

Carbon monoxide gas is odorless, colorless, and tasteless, and every year it kills and injures many dozens of people around the country.

You may or may not be able to smell the exhaust itself in the cabin, but carbon monoxide can be building up slowly the whole time.

This gas is so dangerous because it binds with hemoglobin in the bloodstream and consequently prevents your blood from carrying oxygen to your organs, muscles, and other tissues in your body.

The symptoms of CO poisoning develop gradually over time and in direct proportion with the amount of carbon monoxide gas in your system.

They include dizziness, nausea, fatigue, acute headache, and vomiting at lower concentrations.

When they start to get really bad you might suffer from hallucinations or other visual malfunction, sluggish thoughts, and finally fainting followed by coma. After that, you’re probably toast.

Fatal poisoning often results when its victims are already asleep because they never wake up in time to save themselves.

How Long Can You Sleep in Your Car Safely?

You can sleep in your car safely for as long as you want assuming there is no carbon monoxide getting into the passenger compartment, but if it is, it doesn’t take long before it poisons you.

This is because the overall volume of air inside the cabin of your vehicle is very small compared to your home, and further compounded because you have it tightly sealed up.

If high quantities of CO gas are getting into the cabin, you might have as little as an hour’s worth of exposure before you are fatally poisoned.

Your short nap might cost you your life.

Can You Sleep in Your Car with the Engine Off?

Yes, you can sleep inside your car safely if the engine is shut down, assuming of course you have your car parked in a place that does not have a toxic atmosphere.

With the engine shut off there may only be trace amounts of exhaust gasses containing CO that could it trickle into the cabin, but this will not pose a serious risk to health or life, even with the windows shut.

Is it Okay to Leave the Engine Running with the Windows Cracked?

The obvious response used by most when it receives information is simply to crack a window or two in the cabin in order to allow fresh air in or carbon monoxide out.

Is definitely a reasonable idea, but unfortunately is probably not sufficient to prevent disaster in case of a serious carbon monoxide leak.

Cracking one or even multiple windows open just a little bit will generally not allow enough fresh air in to offset the buildup of carbon monoxide, and nor will it let enough CO contaminated air out to prevent poisoning.

Opening windows up much wider is generally sufficient, however, but then this presents an obvious security risk depending on where you are parking the car to get some rest.

How Can You Prevent Carbon Monoxide Accumulation in Your Vehicle?

The next obvious course of action if you want to prevent carbon monoxide gas from entering your vehicle when you have the windows closed and the engine running is to address any way that this toxic gas can get in.

The number one cause of such accidents is a blockage of the exhaust pipe or pipes on the vehicle. This could be caused by water, snow, mud, or even tightly packed debris like dirt or cloth.

Anything that prevents exhaust gasses from exiting via the tailpipe increases the chances that they could be seeping into the cabin.

Another common cause, the one that is far more difficult for your average person to diagnose, is simple engine malfunction.

All sorts of problems and breakages might allow exhaust gases to seep into the cabin when the car is stopped, or even when it is moving.

Preventing both of these occurrences is relatively simple: in the case of a blocked tailpipe, you’ll want to make it a point to ensure that nothing is obstructing or impeding the flow of exhaust through the tailpipe.

This is particularly important in snowy conditions, flood conditions, or after your vehicle is immobilized off-road. A skid might bury your exhaust pipe in the ground!

Pay close attention whenever you are dealing with heavy rains and serious snow accumulation because your tailpipe may become blocked over time if you don’t check and clear it.

When it comes to preventing malfunctions, all you can really do is keep your car inspected and properly maintained, and you should always take it in if you detect any exhaust odor in the cabin.

Warning: Running Your Air Conditioner or Heater Will Not Disperse CO Gas

Just a word of warning: running your air conditioner or your heater is insufficient to evacuate carbon monoxide from the passenger compartment or bring in enough fresh air to offset carbon monoxide when you have the engine running. It does not matter if you have it on recirculate or not.

If you need cooling or heating, by all means, run it but don’t depend on this as a factor for keeping yourself and other passengers safe.

Will You Run Out of Air Sleeping in a Closed Car?

Considering that your average vehicle will close up tightly enough to make the accumulation of carbon monoxide gas a genuine risk to life and limb, it begs the question of whether or not you could just run out of oxygen inside the same vehicle with the engine turned off and the windows rolled up tightly.

As a rule, no, you won’t run out of air. Pretty much every passenger vehicle is not truly airtight, and that means you won’t run out of oxygen.

However, you will notice a marked drop in air quality if you do not take the time to periodically crack the windows or open the doors and allow fresh air in.

This is because you’ll be exhaling carbon dioxide, and increasing the humidity of the air inside the cabin with every breath.

Considering that suffocation and carbon monoxide poisoning are not mutually exclusive outcomes, your car is sealed tightly enough to make the accumulation of carbon monoxide gas a genuine hazard because it does not allow enough fresh air in quickly enough to offset it.

On the other hand, the air inside your car can still definitely get stale even though oxygen is seeping in from the outside over time.

1 thought on “So, is it Safe to Sleep in a Car with the Windows Closed?”

  1. I always leave an inch or two in two diagonal-opposite windows. This will ensure circulation of more air then I breathe. It is a good failsafe.


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