Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.Sources of Methane gas, LP gas, natural gas uses
Methane Gas Sources, detection, hazards in & around buildings

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This article describes possible sources of methane gas that may be found in or around buildings including methane gas coming from a water well, from a septic system or plumbing drain problem, from gas leaks, or other sources.

We discuss different methane gas sources in buildings and how each contributes methane gas, what the problem is, and how to find and fix that methane gas leak source. We link to in-depth articles about the testing, detection, hazards, and correction of methane gas and sewer gas hazards and their sources in buildings.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Sources of Methane gas, LP gas, natural gas uses, sources, detection, hazards in & around buildings

Natural Gas & LP Gas fuels used in buildings or about Methane Gas (CH4) production from sewers, septic systems, or other sources in or around buildings

Watch out: we warn in all sewer or septic gas odor articles that because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation. Sewer gases also probably contain hydrogen sulfide gas (H2S) In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation). Depending on the sewer gas source and other factors such as humidity and building and weather conditions, mold spores may also be present in sewer gases

Question: what are the possible sources of methane gas in or around buildings?

I'm researching the possible sources of methane gas that might explain gas odors or leaks in or around buildings. Can you list the uses, properties, occurrence of and hazards of natural gas, LP gas, and methane gas that might be found in buildings. Can you refer me to LP, natural gas and methane gas information at InspectAPedia? - Anon.

Reply: Methane gas is widely used as a fuel in buildings and occurs in septic & sewer systems, in some wells, and in thawing permafrost

Sure. At InspectAPedia ou can find information on any of the gas topic names you list by using the search box found at the top or bottom of any InspectAPedia web page. It is worth noting that in addition to the widespread use of methane fuels as LP (liquid petroleum) gas or "bottled gas" and as piped in natural gas in buildings, there are a number of natural or manmade sources of methane gas (CH4) that might be detected in or around buildings, including the biological production of methane by methanogens in septic and sewer systems and the occurrence of methane gas in soils, water wells, and even in lakes, and streams. And in December 2011 the New York Times reported on significant levels of methane gas escaping from thawing permafrost.[1]

Here are some direct referrals to articles discussing LP, natural gas, methane gas uses & sources & hazards at buildings:

Reader Question: help tracing methane gas in a home

8/19/14 Meredith said:

We need help tracing a methane situation in our home. Starting in April we noticed a periodic strange smell in our son's bedroom. After much trial and error, we got an inspector to come and do an air test. Methane level was found to be 3.8ppm, not explosive but higher than usual for indoor air. Now we can't figure out where the methane is coming from!

-Our gas system was pressure-tested, no leak.
-Neighbor who shares our wall (it is a townhouse) pressure-tested her system, no leak.
-Gas lines do not even run in the walls of the room.
-Smell is limited to that one room, nowhere else in the house, and not above or below that room.
-No plumbing near the room, therefore don't suspect sewer gas.
-Smell has a 'mercaptan' odor similar to, but not exactly the same, as the odor added to natural gas
-Smell is there only at certain times of day! Strongest in the afternoon (which happens to be when that room is warmest as the sun hits in the afternoon, but that may be a coincidence), nonexistent in morning, variable at night time.
-Air was also tested for VOCs, came back negative.



Depending on just what testing was done, perhaps we should not be over-confident that we've really correctly identified the gas that makes the odor that you cite. Indeed most people are pretty good at spotting a mercaptan odor and indeed that's added to gas supplies for safety reasons.

But often odors are chemically complex, and many gas detectors and even some lab procedures may focus on methane and detect it and name it when in fact what's present is a more complex substance.

That's why your visual inspection and careful thinking make sense.


we describe steps that might help you pinpoint the odor source, including keeping an odor log. From your note my first guess would be a plastic building material such as siding, window, or window screen that off-gasses when heated by the sun.

Reader follow-up:

Would the VOC test have detected any building materials offgassing? That test came back normal. But I see what you mean-- the methane could be a red herring, but the 3.8ppm level seemed usual to the inspector.

We had thought about the offgassing possibility before we got back the methane test. The materials in the room are exactly the same as the materials in the other (non-smelling) bedroom which is right next door to it, shares a common wall, and also has the identical sun exposure. The house is brick, no siding.

We patch-tested the window and drywall (as per your recommendation), nothing. We've cut drywall open in several places and can't tell even which part of the room the smell is coming from-- it really fills the space. We've removed all of the furniture, the cellular blind, the rug, etc. Checked outlets and light fixtures.

Obviously there is an explanation, but we are stymied. Who else can we call? The person we had out does specifically environmental testing. Is there another kind of specialist we can call in for help who might be familiar with solving these kinds of mysteries?


In the atmosphere in general we see about 2.2 ppm of methane. (CH4)

Depending on the methane source and exactly where and how your consultant measured, the methane results would vary. For example,
since it's lighter than air, with no mixing fans running in a room, if methane were present I'd expect it to be at higher concentrations near the ceiling.

[Propane on the other hand is heavier than air - this is why we place propane gas detectors low in a room and methane gas detectors high]. While we're on it, CO (carbon monoxide) is also slightly lighter than air and will generally mix in air throughout a room.]

If the test was methane specific then there is a methane source - but keep in mind that there are plenty of common sources of methane including organic garbage and human flatulence.

The EPA, in studying methane levels in homes near landfills defined this action level:

Methane: > 1.25% volume in air (12,500 ppm). The LEL for methane is 5% and 25% of the LEL is 1.25% - that's how EPA
got that number.
- "Lower Darby Creek Area - Clearvierw Landfill Site, Final Indoor Ambient Air Monitoring and Assessment
Plan, April 2010, U.S. EPA, Tetra Tech EM, Inc., TDD No. #43-028-10-01-001

A "VOC" test, depending on how it is conducted, can be sensitive to a wide range of volatile organic compounds but I don't rule out other
gases or smells not included in such a test.

While VOCs are chemicals that contain hydrogen H and carbon C and that evaporate easily, Methane, though it is a greenhouse gas, is not properly a VOC. Here is a commonly quoted definition:

Any chemical compound based on carbon chains or rings (and also containing hydrogen) with a vapour pressure greater than 2mm of mercury (0.27 kPa) at 25 deg C, excluding methane. Also excluded from "VOCs" are CO, CO2, carbonic acid and carbonate salts.
- USEPA, AP-42 1996

Keep in mind that not everything that you smell is a "VOC".


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