Did my gas stove emit carbon monoxide?
October 16, 2016 4:03 AM   Subscribe

Is it correct that a stove running on natural gas can only emit CO if the burner is lit? On Saturday morning, I went out to run an errand, and when I came back to my studio apartment, I smelled gas. One burner was very slightly on (but burner was not lit). I wasn't using the stove, but I guess I must have bumped into the burner. I opened windows and called the gas company to ask what to do, and they sent someone out. He showed up ~15 minutes later, and by the time we went inside, the smell had dissipated. Everything tested fine. He told me that an unlit burner would not produce CO- is that right? Is it true that a stove would only produce CO if there is a flame?

There's a small chance the burner was bumped before I went to bed Friday night, and it's a very airtight apartment. I felt completely fine on Saturday morning (I do have a headache now that started Saturday afternoon, but I think it's probably unrelated. I'm housesitting for someone tonight and was only in the apartment for a short time while it smelled like gas). If the stove was on longer, is there anything else in the gas I should be worried about?
posted by pinochiette to Health & Fitness (11 answers total) 1 user marked this as a favorite
Best answer: The gas company employee was correct. CO is a product of incomplete combustion. If the burner wasn't lit, the stove was just leaking out methane. That's obviously dangerous from an explosion perspective, but not from a CO perspective.
posted by Betelgeuse at 4:35 AM on October 16, 2016 [5 favorites]

No, there was no CO/carbon monoxide. The gas that fuels your stove is mostly methane (CH4) and other light hydrocarbons (CxHy). The smell comes from hydrogen sulfide (H2S) which is really stinky and added as a safety feature.

Full combustion of hydrocarbons leads to CO2, carbon dioxide, which is not harmful. CO results from combustion in an insufficient oxygen environment, and it is harmful. If nothing was burning, and you have plenty of air circulation in your apartment, no danger of CO from this incident.
posted by Sublimity at 4:36 AM on October 16, 2016 [1 favorite]

I don't think there's anything else to worry about, reading the question. If you can't smell the gas, by now it's dissipated enough that there's no risk of fire, etc. The hydrogen sulfide that you smelled (again, that's added as a safety feature--specifically to alert your nose that there's a gas leak, since the fuels themselves are odorless) is not harmful in the amounts that you experienced.

It's always nerve-wracking to have a gas leak, even a minor one. But short of developing a habit of double- or triple-checking that all the burners are off, nothing else needs doing, and no harm done. Thanks goodness!
posted by Sublimity at 4:40 AM on October 16, 2016

One of the main reasons that CO is a significant hazard when it is present is that it is odorless. There is no smell to warn you that you are breathing it in.
posted by megatherium at 4:55 AM on October 16, 2016 [1 favorite]

While there wasn't any CO, you could get a CO alarm for your house if this worries you. They're required by law (along with smoke detectors) her in Ontario. They're designed to fail noisy, so when they come to the end of their 6-8 year life, they'll go off with an ear-splitting shriek.
posted by scruss at 5:30 AM on October 16, 2016

Hydrogen sulfide is extremely toxic, and is most certainly NOT added as an odorant to natural gas. The odor comes from added tert-butylthiol.
posted by mr_roboto at 7:35 AM on October 16, 2016 [1 favorite]

Best answer: The suicide-via-head-in-the-oven trope pre-dates the widespread use of natural gas, which as Sublimity correctly points out is mostly methane and relatively non-toxic.

The idea that gas is toxic is a holdover from the days before natural gas was a thing, when gas companies used to supply coal gas. This does contain carbon monoxide as well as hydrogen.

You still don't want gas building up inside your dwelling, mainly because gas-air mixtures are an explosion hazard once the gas concentration rises high enough, but an indoors leak of unburnt natural gas isn't going to poison you with carbon monoxide.
posted by flabdablet at 8:19 AM on October 16, 2016 [4 favorites]

Response by poster: Thanks, everyone! If methane was possibly building up overnight, would that be a health concern? It's a small room (kitchen and bedroom/living room in one area). I didn't smell gas when I left in the morning, but I guess there's a small possibility that I got used to the smell while I was sleeping... (Seems unlikely).
posted by pinochiette at 8:36 AM on October 16, 2016

If methane was possibly building up overnight, would that be a health concern?

Quick checklist for methane toxicity:

1. Am I dizzy or nauseous or hearing internal helicopter noises from lack of oxygen? Yes/No
2. Did I just die in an enormous fireball? Yes/No
3. Can I smell gas? Yes/No

If your answers to all three questions are No, your health is not being negatively affected by exposure to piped natural gas.

Also worth bearing in mind is that methane is less dense than air (molecular weight of 16 compared to 29 for air) so if it's going to pool anywhere in your house it would be under your ceilings, not down at bed level. Carbon monoxide at molecular weight 28, on the other hand, is close enough to the density of air that it will diffuse more or less evenly through a room.

Tert-butylthiol, the gas odorant, is a relative heavyweight at molecular weight 90. If there's natural gas pooling inside your house, you'll smell the odorant even if the methane itself has all gone upstairs.
posted by flabdablet at 9:02 AM on October 16, 2016 [3 favorites]

Full combustion of hydrocarbons leads to CO2, carbon dioxide, which is not harmful.

Not harmful assuming reasonably good ventilation, at any rate.

I would personally find it quite uncomfortable to spend any length of time inside a well-sealed, well-insulated house containing a non-flued gas stove and non-flued gas heaters.

The thing about carbon dioxide, though, is that unlike its monoxide relative it isn't sneaky. If there's too much carbon dioxide in your air, you know it; it feels stuffy and makes you feel like your breathing isn't working properly.
posted by flabdablet at 9:15 AM on October 16, 2016

Don't trust your sense of smell. If you have been in a gassy atmosphere for a while, you may lose sensitivity to it. If you know an unlit burner has been emitting gas, leave without touching anything electrical (especially wall switches) and call the gas company (as you correctly did).
posted by SemiSalt at 4:26 PM on October 16, 2016

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