I keep seeing this conspiracy get repeated. The conspiracy goes like this: car manufacturers don't want homeless people sleeping in cars, so when a car is off, the air vents automatically close. They say you must crack open a window, but this wouldn't be good in the winter time when it's cold, and you can't leave a car running while parked because of the risk of carbon monoxide poisoning. So, a homeless person in the winter time who only has a car would have no choice but to sleep with the car off and the windows rolled up.

Generally when pressed for evidence, this is the article they like to respond with: New Zealand couple manages to lock themselves in keyless car for 13 hour

Is a person at risk of suffocation from oxygen deprivation if they sleep in their car with the engine off and the windows rolled up?

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    Hi Mike, great question, but would you mind clarifying whether you're more interested in evidence "that it is possible to die of CO poisoning in a closed, running car", or that * "car manufacturers actively make changes to their vehicles to prevent people from sleeping in them safely?" * thanks a lot!
    – 0xDBFB7
    Commented Dec 16, 2021 at 19:47
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    There are two distinct claims here. One is that little or no outside air enters a car which is not moving and whose systems are turned off. This is true to a large extent: without either a fan or pressure due to the car moving forward, very little air actually moves through the ventilation system. The question is whether this is so little that one person could suffocate overnight. The other claim, for which you don't show a citation (you should), is that there is some kind of far-fetched conspiracy in which manufacturers make this specific situation worse than it naturally is. Commented Dec 16, 2021 at 20:05
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    The linked story mentions neither carbon monoxide, CO nor poison. The phrase "the risk of carbon monoxide poisoning" is a claim that you have made yourself. Commented Dec 16, 2021 at 21:57
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    Can we get a better notability reference? Perhaps three or four people actually making the claim.
    – Oddthinking
    Commented Dec 17, 2021 at 6:21
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    @Nat - I have slept many times in cars, engine off, windows shut. Sometimes on my own, sometimes in company. Sure, you end up with condensation fairly rapidly, but there is absolutely no problem with getting enough oxygen.
    – Rory Alsop
    Commented Dec 21, 2021 at 12:57

1 Answer 1


According to Measurement of air exchange rate of stationary vehicles and estimation of in-vehicle exposure (1998):

The air exchange rates or air changes per hour (ACH) were measured under 4 conditions in 3 stationary automobiles. The ACH ranged between 1.0 and 3.0 h-1 with windows closed and no mechanical ventilation

The air in a parked stationary car is fully exchanged every hour or so at the worst (through the passive vents in the car). That is more then enough to keep CO2 and O2 levels OK, and you're not in any more danger of asphyxiation in a car that's off than in a bedroom with the windows closed and door shut.

I don't have a good way to rebut the "cars will shut those vents to murder their occupants" part of the conspiracy theory. It's hard to prove a negative. That said, car manufacturers are unlikely to be in a conspiracy to kill their customers, and I think most people have at one time or another slept a few hours in a car (and survived).

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Oddthinking
    Commented Dec 25, 2021 at 20:02

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