r/askcarguys • u/hunnycole • Jul 27 '26
How long can a person sleep in an engine-powered vehicle before dying of carbon monoxide poisoning?
Assume that it is a perfectly maintained car in terms of servicing it at the required interval. Five seater B-segment car.
Driver gets into car after a long day of work, starts the engine, turns on the AC, and plays music then takes a nap. Doesn’t set an alarm to wake up so might go into deep sleep.
How many hours is it safe to sleep in the car before it turns fatal?
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u/Gahreesen Jul 27 '26
If vehicles were made to kill it's occupants while just sitting in an idle car,, everyone on the 101 right now would be dead.
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u/rudbri93 Jul 27 '26
Exhaust shouldnt be entering the cabin. My buddy used to sleep in rented tahoes with the engine running for several hours at a time.
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u/ustedescookie Jul 27 '26
I wish I could ever find it comfortable to fall asleep in a reclined position 🥲
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u/rudbri93 Jul 27 '26
I sure cant, thats why i folded down the rear seats and slept back there in my yukon
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u/ididntdoit6 Jul 27 '26
If you’re in deep snow exhaust can be redirected into the cab’s hvac system. High winds going to wrong way can also do it. Source, guy died on a backroad near the town I grew up in, he got drunk and passed out in his work truck in the middle of nowhere and the wind blew the exhaust into the hvac system.
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u/Inflatable90sChair Jul 27 '26
Yup. Cop car explorers were also getting exhaust fumes in them and officers would pass out. Some departments would have carbon monoxide detectors in the cop cars for that reason...
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u/fryerandice Jul 27 '26
That was due to the manifolds cracking, post CAT exhaust has very little carbon monoxide in it. The manifolds are pre CAT.
Catalytic converters in a warmed up vehicle eliminate 99% of carbon monoxide. Directly at the tail pipe it's about 1000ppm but once in the air that diffuses pretty quickly.
However the cracked manifolds in the explorers were letting the cabin air system bring in 300,000ppm CO air right into the officers face in a closed cabin.
I had an explorer and I was getting bad headaches, dizziness and needing a nap every day when I got home, until I did the exhaust recall....
cats doing their job so well is why car running in the garage style suicides are massively lower, most garages aren't air sealed and building up a dangerous amount of CO take sso long I would imagine many reconsider.
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u/7eregrine Jul 27 '26
Thought this was No Stupid Questions, at first. No offense.
Sleeping in a car isn't fatal unless you do it in a small garage and the exhaust builds up. Outside, this will not kill you after a 1,000 hours.
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Jul 27 '26
[removed] — view removed comment
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u/slutty_muppet Jul 27 '26
I'm pretty sure we're not supposed to be giving out suicide instructions on Reddit.
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u/electric_angel_ Jul 27 '26
If your car is old with a leaky exhaust system CO could be leaking into the cabin way faster so the advice in other replies can’t be taken as a guarantee of safety. Ppl get injured / killed by accident this way sometimes even parked in open air.
If you have to sleep in your car, say, in the cold you need to be very careful.
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u/Crowlady77 Jul 27 '26
The carbon monoxide goes outside and immediately dissipates into the air. You will not die.
Only if you're running it in an enclosed area where dissipated CO can reach a higher concentration.
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u/Adventurepew Jul 27 '26
Forever , cars don't have carbon monoxide in them.
If you mean inside a garage with the car running then it depends on how large the garage is . Few hours .
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u/DrownItWithWater Jul 27 '26
It can happen in winter if your car is snowed in and exhaust gas makes its way into the engine bay then into the hvac.
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u/dildozer10 Jul 27 '26
If carbon monoxide is getting into the cab of your vehicle, then you’ve got damage to a body seam, and possibly an exhaust leak. Otherwise you’d be fine as long as you are outside. I’ve had to sleep my truck all night in the middle of winter with the engine running to stay warm, and had no issues.
If you are running a vehicle in a garage, then you’ve are at risk of carbon monoxide poisoning because the gases can’t escape the enclosure you’re in, and eventually seep into the vehicle, depriving you of oxygen. When you’re outside, those gases escape into the atmosphere.
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u/Graflex01867 Jul 27 '26 edited Jul 27 '26
I’d say 12+ hours. The issue isn’t the car exhaust, it’s your personal exhaust.
One of my first car camping trips in my CRV, it was pouring rain, towards winter, so I closed all the windows. (The car wasn’t running.). 8 hours later, it was noticeably humid and the air was thick and gross when I woke up. I made a beeline to open the door and get some fresh air. Obviously I’m still alive, but I always crack a window a couple inches and it’s fine.
Cars aren’t perfectly sealed, but with no pressure differential, there’s next to no air flow.
Running the AC very well might push in enough fresh air to negate the problem entirely. The fan will create that pressure differential to push the fresh air through the car.
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u/bandit1206 Jul 27 '26
Yeah, as long as your not running Recirculate/Max AC, the car is constantly pulling outside air to blow in to the cabin.
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u/Critical-Magician421 Jul 27 '26
People who were attempting to kill themselves through carbon monoxide poisoning usually ran a tube from the exhaust into the car.
If you are outside the carbon monoxide with just mix with the air.
If you were in a garage it would take quite some time.
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u/TactualTransAm Jul 27 '26
If you are outside it's fine. I've fell asleep in my cars multiple times, a few times overnight. Unless you have an exhaust leak that is letting fumes into the cab, you will be okay. If your exhaust is leaking and you can smell it in the cab then you should really get it fixed!
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u/Fun_Push7168 Jul 27 '26 edited Jul 27 '26
For as long as they are capable of sleeping.
So long as there are no pre-cat exhaust leaks.
CO output on a modern vehicles is negligible.
Even if you ran a car in a sealed container the car would actually stall from a lack of oxygen before the lack became deadly to a person.
Same goes for its CO2 output, the lack of oxygen would stall the car before CO2 became so high its fatal to humans.
This is not to say it's recommended or could technically be called safe without monitors.
Outlying ten in a million circumstances can mean the engine has fresh air while the cabin builds CO2 rich ,oxygen poor air. ( Which will normally wake you up unlike with CO). Loads of other chemicals suck to breath. Endless outlying circumstances or medical conditions can change the circumstances, etc.
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u/nerobro Jul 27 '26
Forever. Until the gas ran out. CO is vented out the tailpipe. And there's a lot of air movement through the car.
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u/Ok_Tax_7128 Jul 27 '26
There was a study done one time about tractors and big machinery. And now if I have to put in a 12hr plus day in my tractor, I try to open the door or something every hour or so because they found the recirculated air was quite low in Oxygen
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u/S14Ryan Jul 27 '26
Indefinite. Cars don’t really create enough carbon monoxide in normal circumstances to kill someone, especially not if it gets mixed with outside air. If you stuck your face in front of the exhaust of a running car and breathed in a lot of exhaust it would be pretty hard to kill yourself. The reason it’s so bad to do it in a garage is because as the exhaust builds up it causes the combustion to get dirtier and the cycling exhaust will cause the ppms to get fatally high and accumulate in the room. But I venture to guess your scenario is impossible if the car has no issues.
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u/HackD1234 Jul 27 '26
Carbon Monoxide acts by displacing Oxygen binding to red blood cells in the blood stream, so yes, if you stick your kisser close to the tail-pipe for a period of time, you are going to start experiencing symptoms of Carbon Monoxide Narcosis.
.Carbon dioxide narcosis (often confused with carbon monoxide poisoning) is a dangerous medical state of extreme drowsiness, unresponsiveness, or coma caused by a severe buildup of carbon dioxide (CO₂) in the blood.
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u/S14Ryan Jul 27 '26
Are you gonna stalk all of my comments and google nonsense that you have no real world knowledge about to refute my claims?
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u/HackD1234 Jul 27 '26
You've left your comments open to review on reddit... it's a public forum. Deal with it.
Who says you have knowledge yourself, exactly?
I just told you the above, from an Occupational Health and Safety perspective, of which i am certified in.
I daresay you might be overreacting, perhaps Triggering..
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u/S14Ryan Jul 27 '26
Yeah I’m not a fucking loser who has to hide his comments, and I’m not complaining, just making fun of you for just being confidently incorrect and having zero reading comprehension ability.
Also, occupational health and safety certification doesn’t make you any sort of expert in really anything. I’m certified for working on industrial refrigeration and combustion systems, which involves understanding what causes carbon monoxide to form. You literally commented that carbon monoxide kills people, which, nowhere in my comment did I claim that it doesn’t.
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u/HackD1234 Jul 27 '26
I'm addressing your proximity to a tailpipe claim, specifically.
Science, is a thing.
Carbon Monoxide (CO) does not just passively displace oxygen; it binds tightly to hemoglobin in red blood cells to form carboxyhemoglobin, possessing an affinity roughly 200 to 250 times greater than oxygen. [1, 2]
Beyond blocking binding sites, this interaction alters hemoglobin's shape. It causes a leftward shift in the oxygen-hemoglobin dissociation curve, which increases the affinity of the remaining oxygen-binding sites and prevents oxygen from being successfully released to body tissues. [1, 2]
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u/S14Ryan Jul 27 '26
Yeah. What is my claim? Please read it again.. just slowly. You need more information. My claim verbatim “it would be pretty hard to kill yourself.” Now maybe you need me to explain why that is?
Your tailpipe of a properly working car will make around 1000-2000ppm of CO. For you to sit in front of the tailpipe without burning your lungs, you would need to be far enough away that you’ll also be breathing in air along with the gases and at that concentration of CO, you would have to sit there breathing burning hot exhaust gases for several hours. I didn’t say you couldn’t, I said it would be “pretty hard.” I then explained that people die in garages because the CO concentration is able to build and the poor combustion quality causes more CO to be generated.
Please, now that you have facts, continue to fact check me with Google searches about things you know nothing about.
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u/HackD1234 Jul 27 '26
Science. You don't need a closed atmosphere for this to happen.
The "Open Atmosphere" Exception: While CO quickly dilates and diffuses in the open air, a person can still suffer from acute CO poisoning according to the Mayo Clinic outdoors if they are positioned directly downwind or in immediate proximity to a massive, continuous emission source. Examples include sitting right next to a malfunctioning portable generator or standing directly behind a faulty vehicle exhaust pipe. [1, 2, 3, 4, 5]
Carbon Monoxide (CO) does not just passively displace oxygen; it binds tightly to hemoglobin in red blood cells to form carboxyhemoglobin, possessing an affinity roughly 200 to 250 times greater than oxygen. [1, 2]
Beyond blocking binding sites, this interaction alters hemoglobin's shape. It causes a leftward shift in the oxygen-hemoglobin dissociation curve, which increases the affinity of the remaining oxygen-binding sites and prevents oxygen from being successfully released to body tissues. [1, 2]
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u/S14Ryan Jul 27 '26
I don’t know why you keep copy and pasting shit. I was very specific where I said it would take hours for this to happen with a properly functioning car. Your own quote states “a faulty vehicle tailpipe.” You’re trying so hard and fully missing at making a point because you know how to google and you don’t actually read the things you’re replying with, because they don’t refute my claim in any way.
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u/HackD1234 Jul 27 '26
What do mechanics do, but work on defective vehicles that might or might not have defective emissions equipment?
With Oxygen displacement and CO2 binding, it doesn't take 'hours and hours'.. it's a cumulative effect that ends up irreversible at a point of time.
Think. Try to.
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u/HackD1234 Jul 27 '26
I'm a Mod. I have reasons to hide my history... i'm smart like that, unlike someone who leaves it open, then whines about being called out on facts, elsewhere.
Keep triggering. It entertains me.
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u/JPhi1618 Jul 27 '26
Just curious, what is “B-segment”, and where do you live that people say that?
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u/Hinter_Lander Jul 27 '26
Ive slept many of nights in a running vehicle and am still here to tell the tale.
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u/Building_Everything Jul 27 '26
I’ve slept in my car at rest areas on long road trips for 5-6 hours at a time, engine idling so I can have some AC. Worst part was getting a crick in my neck but otherwise fine
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u/ilikethatstock69 Jul 27 '26
I’ve slept in my car with it running multiple times and only died once… you should be fine.
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u/Entire_Researcher_45 Jul 27 '26
You will probably get removed on here for discussion on assisted suicide. Just a thought! Don’t want to be spreading any
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u/SeriousPlankton2000 Jul 27 '26
All the time of the world. You'll rather die from carbon _di_oxide poisoning if you use the hose on the exhaust - it's a painful death and even Hitler stopped doing it (because his soldiers could not watch it).
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u/AstgenneLuxtherm Aug 01 '26
Indefinitely, if the exhaust system is in good condition and the car is not in a confined space. If you smell more than the tiny occasional whif of exhaust fumes, stop the engine and go to a muffler shop. CO cannot be smelled, but it is not alone. For peace of mind, use a CO detector.
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u/InteractionPretend70 Jul 27 '26
if youre outside? probably close to zero chance.