Question Update: We now know that the problem is Carbon Dioxide; any suggestions on what could be consuming oxygen and producing Carbon Dioxide would be great!

We rent an old farm house that has recently been renovated, the cellar has been tanked, it would be perfect as an office, but I'm out of breath just typing this question.

It seems that either a build up of some other gas is excluding the oxygen. Does anyone have any ideas? It doesn't seem normal!!

I'm guessing it's oxygen (or lack of) as I'm unable to even light a match in the cellar.

It does seem to be worse when it's wet weather.

There is NO obvious source of gasses, as the house has electric heating, cooking and hot water

I've also asked this related question on the Chemistry Stackexchange site


We've had the Environment Health monitoring the Cellar and the rest of the house for some weeks now. They have now served a prohibition order preventing us from using the cellar. They recorded levels approaching 10%, today we have had a surveyor at the house appointed by the landlord and they initially speculate the source could be soot used in the foundations. Any thoughts?


An insepector from the local council has installed a data-logger, whilst he was in the basement he took a reading that I've attached below. When this reading was taken the air felt poor, but by no means the worst it's been, a candle wouldn't stay alight. An breathing during conversation seemed laboured. It looks like the assumption of displacement doesn't look correct, there's more to it. Here's the readings:

Gas - Reading (Normal)

CO2 3.3% (0.04%)
O2 17.5% (20.8%)
Other 79.2% (unchanged?)

enter image description here

  • Any source of combustion gases? Any CO and/or flammable gases detectors?
    – DJohnM
    Mar 31, 2014 at 20:33
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    I've got environmental health coming to do an assessment, I'll update the question/answer. an +1 would be good :)
    – Dog Ears
    Mar 31, 2014 at 20:52
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    @FiascoLabs a bit of goggling suggests Methane is lighter than Air, would CO2 be more likely?
    – Dog Ears
    Mar 31, 2014 at 21:04
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    Your local Fire Department might be equipped, and willing, to test that basement for CO/Methane and perhaps Radon. Either way, you should be checking until you find why. As above, don't enter the basement without a helper above. Start DIY by tossing one of your battery powered CO detectors down.
    – Bryce
    Mar 31, 2014 at 23:07
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    Just found this .... caves.org/section/medical/air.htm very interesting, would indicate that oxygen levels in my office/cellar are very low..! [can't light a butane lighter, match quickly fizzles out without lighting]
    – Dog Ears
    Apr 1, 2014 at 8:19

4 Answers 4


If you're feeling lightheaded/out of breath in the basement, I'd stay out of there until it's well ventilated and never enter the area without someone on the outside to monitor you and call for help if needed (but that person should not enter the area). If it were my basement, I'd call the fire department to check for Carbon Monoxide and/or combustible gas and assist with ventilation.

One possibility is that Carbon Monoxide has accumulated in the basement, perhaps due to a faulty heating appliance and poor ventilation, or gasoline powered equipment in or near the house. This is extremely hazardous and potentially fatal -- it can cause you to become incapacitated and unable to leave the space.

Some signs of CO exposure include:


Shortness of breath

Personality changes

Unusually emotional behavior or extreme swings in emotions


Malaise (a generally sick feeling)


Clumsiness or difficulty walking

Vision problems

Confusion and impaired judgment

Nausea and vomiting

Rapid breathing

Chest pain

A rapid or irregular heartbeat

Another, less likely possibility is Carbon Dioxide (CO2). CO2 is heavier than air and can pool in low areas such as unventilated basements. It would take a fairly high concentration of CO2 to prevent a match from igniting. It is less dangerous than CO in that the CO2 doesn't bind to your blood like CO, but overexposure to CO2 can incapacitate you, preventing you from leaving the area.

CO2 can be generated by a combustion appliance like a natural gas or propane fueled dryer or heater with a faulty exhaust vent. Other sources could be something that uses CO2 gas directly like gas from MIG welder, home brewing equipment, home water carbonator, etc.

You could have a natural gas/propane leak. I'd avoid any open flame or anything else that serve as an ignition source (wuch as turning on a switch or even a flashlight) just in case the problem is caused by a combustable gas. Propane is also heavier than air and can pool in lower areas (Natural gas is lighter than air and tends to dissipate, except when the gas is cooler than air and more dense, so it can pool). It is possible for the odorant used in natural gas and propane to fade, so lack of distinctive gas odor doesn't necessarily mean that no gas is present.

There are certainly other gases that could also be causing the problem such as sewer gases, or other gases that come from the ground, or heavier than air gases that are released anywhere near the house.

  • 1
    This is near a dairy, manure pits are a good source of carbon dioxide and hydrogen sulphide, both heavier than air gasses. All you have to be is down wind for it to accumulate in a depression. I'd like to see what the assessment he's asked for reveals. Mar 31, 2014 at 21:23
  • A lack of oxygen would prevent a flame? but a bit of googling suggests that oxygen would need to be down to below 16%, so if it's CO2 that would required an increase from 0.04% to 4% to reduce the oxygen, that's 100x increase, does that sound feasible? I'm thinking it's more likely to be CO2, I've had the window open for a while now and it feels much fresher (and colder!)
    – Dog Ears
    Mar 31, 2014 at 21:31
  • Limestone walls in the basement? That and acid rainwater wil make carbon dioxide aplenty. Nasty stuff: abcnews.go.com/Technology/story?id=119923 Apr 1, 2014 at 12:50

A bit of Environmental Health & Safety perspective: Normal air has 21% oxygen, and anything below 19.5% is considered IDLH ("Immediately Dangerous to Life or Health"). The real danger is not that you would immediately pass out, but rather that your thinking is impaired and you may not be capable of removing yourself from the area. A match will burn well below 19%, probably down to 15% or less, so it cannot be used to judge your safety.

There are a number of possibilities. The air may be unusually high in carbon dioxide (unusual) or nitrogen (even more unusual), presenting no more than the usual asphyxiation danger. It may be high in carbon monoxide, in which case it is far more dangerous, being able to actively strip oxygen from the hemoglobin in your blood. (In extreme cases there can be so much CO compared to O2 that the effective oxygen concentration is negative.) Finally, there might be a combustible gas like methane (CH4) and hydrogen sulfide (H2S). In that case you have an explosion hazard in addition to asphyxiation.

There are three possible cases for combustible gases. First, there may be trace amounts, below the LEL. In that case the gas will not spontaneously combust and the primary danger is oxygen deficiency. Second, you may be above the LEL such that even a spark could set off an explosion. This is an extremely dangerous situation. Professionals usually leave the area and call the fire department if they are above one-tenth of the LEL because of the danger of a local buildup. Finally, the concentration could be so high (above the UEL) that the gas has displaced enough oxygen such that it can't even burn readily. In that case not only is there far too little to breathe but the surrounding area will be above the LEL and liable to explode. (Technically, deflagration is more likely than explosion but let's not quibble here.)

What can you do? First of all, take the situation seriously—unless you have metering equipment to verify oxygen levels, don't suppose they're high enough. Start by ventilating the area, and avoid sparks until the air has been exchanged at least a dozen times (20+ hours). I would let it ventilate passively for a day then take a fan to it. Second, you should get a CO meter (from your hardware store, about $30). Carbon monoxide doesn't stay around long, so if that was the problem it's likely being produced by one of your appliances (usually the furnace). Third, if you find yourself in the same situation again, leave the area immediately and leave investigation for later.

  • A blanket "19.5%" threshold makes no sense. It's oxygen partial pressure, not oxygen percentage, that matters for health. If 19.5% oxygen at sea level is the minimum safe partial pressure, then nobody should ever go above an altitude of 2000 feet.
    – Mark
    Apr 1, 2014 at 5:51
  • Nothing will burn, a couple of butane type lighters that work perfectly well in the rest of the house will not light, a safety match when struck just fizzles out. Any open flame on descending the stairs into the basement just sort of drifts off and extinguishes.
    – Dog Ears
    Apr 1, 2014 at 6:11
  • @Mark: Our laboratories tend to stay at the same altitude.
    – Charles
    Apr 1, 2014 at 13:38
  • @DogEars: That suggests extremely low levels of oxygen. Open the windows and use a box fan?
    – Charles
    Apr 1, 2014 at 13:40
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    FWIW, using an open flame to test for the presence of unknown gases is extremely dangerous!
    – Reid
    Apr 3, 2014 at 13:10

Carbon dioxide is only a possibility, you should take in account there are other various gases that could prevent the match to ignite. In fact maybe there many gases that contribute to the lack of oxygen in your cellar. You should first do a qualitative analysis before performing a quantitative analysis. Here I have wrote a little list of gasses with the related method to detect them, and the sources:

  • vapor, yes this is a gas too and can displace oxygen as well. method: (quantitative) measure it with an hygrometer so you can however diagnose more efficiently the quantity of the unknown gas. source: heat and water can generate it, look at possible infiltration near hot tubes.

  • carbon monoxide this could be more dangerous method: 30$ carbon monoxide detector can help you to identify it source: incomplete combustion

  • carbon dioxide even this is toxic method: another detector 20-40$ source: combustion, respiration, biodegradation, plants during night, leaks from the ground.

  • methane this can explode mixed with oxygen, but can displace oxygen as well, and prevent a match to ignite, it is odorless if from natural sources method: another detector 2-40$ source: biodegradation (e.g. corps), leaks form the tubes, leaks from the ground.

  • radon It is a radioactive, colorless, odorless, tasteless. Can cause cancer. method: detectors can cost a lot but there are some 10 $ kits that can be very effective for a first esteem. source: leaks form the ground, occurring naturally as an indirect decay product of uranium or thorium.

  • hydrogen sulfide very dangerous method: your nose, keep an egg for a month in you fridge open it for reference source:leaks from the ground, biodegradation.

Maybe there are some spot test (methods that use chemists to have a qualitative or quantitative esteem of a specific substance) that you can do at home cheaply, but I would reccomend you to call specialized commpanies or organizations.


How about testing for Radon? High level of Radon will make you choke and it will make you feel like there is no oxygen. It can also causes lung cancer. Please check because not a lot of people are aware of this especially if you are living in an old house. Radon gas is very dangerous.

  • 1
    This is just wrong. Radon is a radioactive but inert gas. Like all inert gases, it is odorless and will not cause animals to choke nor will it interfere with respiration of oxygen.
    – feetwet
    Aug 14, 2017 at 14:08
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    A ballpark estimate is that if there is enough radon in the air to cause breathing problems, you'll be absorbing radiation at a rate of around 1 Gy/s -- the area is radioactive enough that you probably won't make it out of the basement alive.
    – Mark
    Jan 9, 2018 at 2:19

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