Photograph of Don't fall into a septic tank - it's likely to be fatal.Methane Gas & Sewer Gas Danger FAQs

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Sewer gas & methane gas questions & answers:

This article answers commonly-asked questions about methane gas hazards: dangers of explosion or asphytxiation from methane gas from various sources such as septic tanks and sewers.

This article series explains Methane Gas & Septic System Dangers from Gases, gives basic advice, and cites additional reference material.

This article is part of our Septic Safety article series that outlines safety warnings & procedures for septic systems and cesspools, and provides safety suggestions for septic system inspectors, septic system inspections, septic pumping contractors, and home owners.

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Methane Gas Hazard FAQs

Open sewer cleanout in basement (C) Daniel Friedman

Watch out: as we report at SEWER GAS ODORS, potentially explosive levels of gases can accumulate in a building from several sources including explosive levels of sewer gas, swamp gas, or fuel gas from a variety of possible sources including plumbing leaks, improper plumbing venting, LP or natural gas piping leaks or errors, or even swamp gas accumulation under a building.

Recently-posted questions & answers about methane gas hazards

On 2017-02-19 16:19:15.817070 by (mod) - explosion sounds from yard

Karyn, I cannot guess what may be making the sounds you describe. A methane gas explosion would be dramatic and would require both an accumulation of methane gas and a source of ignition - a spark or flame.

Before testing for methane I think an on-site inspection by an expert, or if you think there are actually explosions occurring, vacate the property and call emergency services immediately.

On 2017-02-19 11:13:02.923211 by Karyn

I keep hearing explosion like sounds outside my house. My septic system is outside and last year I had work done on it could this be related? Is there a test I can have done for gases to conclude that this is the reason for the noise?

On 2016-11-08 14:29:01.154835 by (mod) - building a block patio over the septic tank

The dangers I can suggest are outlined in the article above: creating a spark - and thus an explosion are immediate risks; I'd also want to be sure that not only is there easy access to all of the cleanout openings (there may be 3) but also to the tank ends and entire cover should later repair be needed.

If your "block" patio means simply dry-laid concrete blocks, and IF the septic tank cover is one rated as strong enough to support the weight and traffic involved you may be OK.

Be sure to avoid heavy traffic including machinery running over septic lines, tank, or over the drainfield.

On 2016-11-08 06:58:30.808990 by Bryan

I have a new house with a septic system. I want to build a block patio over the tank leaving access to the cover and use the patio for a fire pit area. Any dangers of gasses from the septic tank?

On 2016-07-31 14:17:02.882346 by (mod) - lingering methane gas problems

Interesting question and not one for which I've found expert advice. Perhaps if your outhouse floor plan includes a durable impermeable vapor barrier you'll avoid a potential methane hazard. In any event a generator cannot be safely run inside an enclosed space without fresh air and combustion air.

On 2016-07-30 17:12:51.172416 by Diane

I have a question about filling in an old outhouse. After we fill it in, we would like to convert the outhouse to our generator "doghouse." That would involve filling in the hole, covering the hole, insulating the room (to cut down noise), and adding some vents in the walls.

I'm wondering if there's any problem with potential lingering methane gas and using a gas-powered generator. Anyone have ideas/experience we should consider? Thanks!

On 2016-01-22 23:10:12.493973 by (mod)


It is common in many countries and communities to install plumbing that does not meet North American or European standards, including missing or inadequate venting; the risks are just what we think: poor drainage, sewer gas backup into the building, odors, and in some cases even an explosion risk.

Venting into an attic is also a bad idea: the vent needs to extend to outdoors not to dump sewer gas and moisture into an enclosed space.

I'd prefer to vent fixtures to the outdoors.

On 2016-01-22 06:48:38.118553 by Gene Pothier - methane gas hazards in the Philippines


I recently retired to the Philippines and purchased a home here and is under construction. During one of my routine inspections I noticed a few things that just did not seem correct to me with the plumbing.

Listed as follows (Please note: all homes here use a septic tank):

1) Sinks, toilets and shower drains have no vents.

2) Only source of venting is through the main drainage system which vents into the attic. Attic has no source of ventilation except from soffit openings at the 4 corners of the roof. There is no way for the heat to escape or any form of proper ventilation to take place and it does get hot here.

My question(s) is/are simple; as follows:

1) Does this pose a hazard of any kind? If so what are they?
2) Any suggestions as to a "fix" of improper plumbing?

My 1st question is the more important of the two as your reply will probably answer question 2.

Thank you in advance for any help/suggestions.

Gene Pothier

On 2016-01-09 15:15:20.087215 by (mod)

Brian you ask an important question, not to mention the un-mentioned one of the very large volume of water being wasted daily.

One cannot answer the question without knowing not just what contaminants may be in the waste-water stream but also what pre-release treatment is going to be done to the wastewater before it is released to the environment.

Surely a project such as this one had to file an environmental impact statement - if you're in the U.S. - and that's a public document. Check with your local building authorities to ask where you can obtain a copy. Keep me posted.

Also see

On 2016-01-09 12:47:36.715232 by Brian

I live near a proposed fuel cell energy park. To convert the natural gas into hydrogen, the process will consume 300,000 gallons of water a day and discharge 150,000 gallons of wastewater to its wastewater infiltration system. Is this wastewater toxic? Will it give off any smell? Will it seep into our groundwater? I have a well; will it contaminate it?

At OUTHOUSE / LATRINE FIRE & EXPLOSION we describe a methane gas explosion in an outhouse - admittedly an unusual event.



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