I'm driving an 04' Subaru Forester, and it needs some cleaning on the inside. I'm in my apartments underground parking garage, and I'm wondering, am I safe to idle the car (for the AC, lights on without worrying about battery) for ~30 minutes while I clean the inside? It's really hot outside, so that's why I prefer the garage.

Maybe I'm being overly cautious, but, is this enough room to avoid carbon monoxide poisoning? I've always read it's really only a risk in single or double car garages.

  • Yes you are fine. Consider the AM as cars are leaving for work. They are putting out a lot more C02 than your one car idling.
    – paparazzo
    Commented Jun 26, 2016 at 6:26
  • The size of the garage aside, it also matters how much ventilation occurs in it (i.e. how many times the air is refreshed in a period of time) Commented Jun 27, 2016 at 0:55

5 Answers 5


Is your Check Engine Light on?

That's a rhetorical question, what I mean to say is that if your ’04 Forester is in good tune, it really should not produce that much carbon monoxide.

Also, there are really no long-term health hazzards of non-chronic carbon monoxide exposure, other than death. (It binds with red blood cells in a way that prevents transport of oxygen.) However, short of death, recovery is fairly quick and leaves no "mark" so to speak.

That garage area is huge. I would not be concerned. If you start feeling queasy or get a headache, you should shut off the ignition and get some fresh air outside. The dosing rate of CO on a modern fuel injected vehicle in good tune is very low, such that it's unlikely you would pass out before noticing you are not feeling well. In fact, morbid as it is, attempting suicide nowadays by running your modern car in the garage is likely to fail. The first health hazzard will be the consumption and displacement of oxygen; displaced by carbon dioxide, which is not nearly as toxic in the literal toxicology sense, but a hazzard if it displaces all available breathing oxygen.

If you are very concerned, you can take the vehicle for a jaunty spin around a few miles, to get the vehicle in what's called "Closed Loop" — which will monitor and control CO emissions more precisely. Your '04 Forrester has an electricaly heated oxygen sensor which will do this on its own, it just takes a bit longer.

Your safety is not mine to play with. CO detectors are cheap enough, available at most hardware/DIY stores, and run off a 9V battery. Once you're done detailing the interior, you can move it upstairs and run it in your apartment/home. (The detector, not the Subaru…)

  • Wow! Great answer, and yes she should be in good tune. Might stop by Canadian Tire and pick one up just for the hell of it.
    – Insane
    Commented Jun 25, 2016 at 22:23
  • 2
    I'm jealous. Gotta love a store that you can get a Carbon Monoxide detector, spark plugs, real bacon, and Labatts all in one go.
    – SteveRacer
    Commented Jun 25, 2016 at 22:44
  • It's a better Pep Boys with worse auto service ;)
    – Insane
    Commented Jun 25, 2016 at 22:51
  • 1
    "Also, there are really no long-term health hazards of carbon monoxide exposure" That's not true. Significant CO exposure can cause long-term damage to the brain or other parts of the body. See ncbi.nlm.nih.gov/pmc/articles/PMC2707118 as an extreme example Commented Jun 26, 2016 at 8:35
  • 1
    @Pikamander2 I stand by my statement, although I did add the words "non-chronic". Your cite refers to a single suicidal woman with a whole cocktail of drugs found in her system. There are dozens of legitimate articles which state "full recovery" after even intense (but non-lethal) single exposure -- actual monitored tests, not a woman bent on poisoning herself to death. Your definition of significant refers to chronic I'm guessing. In any case, none of this is really on topic.
    – SteveRacer
    Commented Jun 27, 2016 at 0:53

You would probably be okay, given the assumptions posted by others, like perfect air mixing throughout the garage. But are you willing to bet your life--and that of anyone else who may walk in--on assumptions like that? Remember carbon monoxide has no odor, and exhaust from a well-tuned modern engine doesn't smell much either. Buy a CO detector, and then you'll have it for your home/apartment when you're done. One of my classmates lost his mother and nearly both parents to CO poisoning, and nobody knew anything was wrong. It can strike without warning. Don't just blow it off.

Just because your Check Engine is originally off doesn't mean it's safe. As the engine consumes the oxygen in the room, it becomes oxygen-starved and starts producing CO. Maybe your garage is sufficiently ventilated, but why take the chance?

Incidentally, if you buy a used CO detector, check it in an enclosed space first, even just a candle burning under a pot. Consumer CO detectors have a finite lifetime and need to be replaced after 5-10 years, depending on model. Unscrupulous sellers can defeat the timer and resell an expired detector.

  • Good insight, I mean, I was cautious enough to post here and i'll go out on a limb and say most people wouldn't think twice about it. I was hoping they might make mini ones not the big ones you plug into the wall or whatever, so that I can just keep it in my car.
    – Insane
    Commented Jun 26, 2016 at 5:03
  • 1
    Yeah. Even the big ones can be plugged into a 9V cigarette lighter adapter in place of the backup battery and stuffed under a seat.
    – Anonymaus
    Commented Jun 26, 2016 at 5:09

I can't really say "you'll be okay", because it's about how our body reacts, but I'd say yes, it's enough. There are underground parkings where engines are running all the time. Also you can buy a little carbon monoxide sensor which will yell at you if it's too much.

Just type "carbon monoxide sensor" on eBay; there are plenty of them for a cheap price. All are supposed to do the same job. Basically, they are similar to smoke alarms, but just aims at different stuff. I have both at home.


A different perspective:

Generally when I clean the inside of a car, most or all of the doors end up being open, with me crawling in and out with the vacuum or whatever other cleaning equipment is needed.

In such a situation, A/C is completely useless. The heat that the A/C system does manage to pull out of the interior air is exhausted from under the hood, or elsewhere under the car. This heat, in addition to the heat produced simply from idling the engine will increase the net heat energy locally around the car, and if the doors are open, the A/C will have little chance fighting against that. This is basic thermodynamics.

If it were me, I'd do the following:

  1. Plan to clean the car in the early morning before it gets too hot, so I get the benefit of natural light, but its not too hot to work yet

  2. If 1) is not possible, then I'd leave the engine off, get work lamp (I have one of these super-cheap aluminium clamp lamps) and a nice long extension code, as necessary. Presumably you'll need electrical power anyway if you're using a vacuum.


As with all things.Safety is the primary concern. It would be advisable to do your vehicle cleaning outside in the fresh air. As in the article cited below (Wikipedia) Exposure to Carbon Monoxide is cumulative and could overwhelm you long before you are aware of it. By that time it may be too late. The volume of CO in the structure is of less concern than the level absorbed by the blood. While you are working on your car you are inhaling the gas and you are closer to the source of the gas. The other issue is the other occupants of the apartment complex. They are being exposed unnecessarily to your exhaust. While it may be hot side you can compensate by keeping hydrated.


Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is colorless, odorless, and tasteless, but highly toxic. It combines with hemoglobin to produce carboxyhemoglobin, which usurps the space in hemoglobin that normally carries oxygen, but is ineffective for delivering oxygen to bodily tissues. Concentrations as low as 667 ppm may cause up to 50% of the body's hemoglobin to convert to carboxyhemoglobin. A level of 50% carboxyhemoglobin may result in seizure, coma, and fatality. In the United States, the OSHA limits long-term workplace exposure levels above 50 ppm. Within short time scales, carbon monoxide absorption is cumulative, since the half-life is about 5 hours in fresh air.

The most common symptoms of carbon monoxide poisoning may resemble other types of poisonings and infections, including symptoms such as headache, nausea, vomiting, dizziness, fatigue, and a feeling of weakness. Affected families often believe they are victims of food poisoning. Infants may be irritable and feed poorly. Neurological signs include confusion, disorientation, visual disturbance, syncope (fainting), and seizures.

Some descriptions of carbon monoxide poisoning include retinal hemorrhages, and an abnormal cherry-red blood hue. In most clinical diagnoses these signs are seldom noticed. One difficulty with the usefulness of this cherry-red effect is that it corrects, or masks, what would otherwise be an unhealthy appearance, since the chief effect of removing deoxygenated hemoglobin is to make an asphyxiated person appear more normal, or a dead person appear more lifelike, similar to the effect of red colorants in embalming fluid. The "false" or unphysiologic red-coloring effect in anoxic CO-poisoned tissue is related to the meat-coloring commercial use of carbon monoxide, discussed below.

Carbon monoxide also binds to other molecules such as myoglobin and mitochondrial cytochrome oxidase. Exposures to carbon monoxide may cause significant damage to the heart and central nervous system, especially to the globus pallidus,often with long-term chronic pathological conditions. Carbon monoxide may have severe adverse effects on the fetus of a pregnant woman.

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