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Finding Source of Poisonous Gas

jsinger28 | Posted in General Questions on

We have a very potent gas that can not be smelled that happens infrequently, but causes burning in throat and very severe coughing and burning.

It is strongest in shower (crawl space), but has been felt in laundry room.(slab)  Both about 8 years old.   It happened the other day a few hours after use of the shower.  The shower has a trap but the vent is really far away- a good 15 feet away.  No leaks in crawl space under shower. We can’t tell if there is a trap in the washer line. I put a gasket around washer drain tube to block any gas from coming up.   I believe the washer and shower share same drain out.

About a year ago we had cesspool overflow and they took a bunch of waxy material out

We have had chimney relined, no CO by testers, cesspool tank drained, air tested, really at a loss.  In the past when cesspool full we have had sewer smell in that bathroom.  One plumber questioned whether the washer had a vent in wall.

What do we do next.  Sewer company  wants to do video.

Please help- scary

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    Check if you have any drains that are seldom used. What can happen is the water in a trap for something infrequently used can evaporate over time, and eventually the trap goes dry and sewer gas can come in. Running water somewhere else can sometimes act to push that gas in through the dry trap. All you need to do in this case is to pour water down those seldom used traps on occassion to keep them full.

    Blocked vents can be an issue too. This could be bird nests or similar blocking a stack vent on the roof. Another possibility is a stuck AAV (Air Admittance Valve), which is a sort of "ventless vent" that is sometimes used on interior plumbing such as a sink, especially a sink in an island. If an AAV gets stuck open, you end up with a path for sewer gas to get in.

    I think a video inspection of the sewer line is probably a good idea. If you have a blockage (roots, crushed pipe, etc.), that could be part of the problem too. You want to fix anything like that before you have a big problem.

    Bill

    1. jsinger28 | | #2

      Thank you very much for replying. I dont think its lack of water in the traps as I filled the shower when this started happening.

      Would a AAV be in the crawl space under the shower?

      The cesspool guy suggested filling vent with water to see if clogged. Any thoughts on that.

      The washer drain is in the wall abutting garage that has plaster board. Maybe I should open to see if there is a vent?

      D you know anything about a smoke test?

      Thanks again.

      1. Expert Member
        BILL WICHERS | | #4

        I doubt there would be an AAV on the shower. The issue with the traps could be somewhere else. For example, if you have a shower AND a bathtub, but rarely use the bathtub, the shower trap is probably full but the bathtub trap might not be. Make sure you didn't miss any traps.

        I don't see any downside filling a vent with water. I'd have a helper watch inside though to make sure nothing comes out the wrong way since you don't know where a blockage might be. If there is a blockage downstream of the vent somewhere, it's possible filling the vent might overflow a sink (or something else), especially if there are any wet vents involved.

        Smoke tests are a way to look for hidden leaks. You basically fill the pipe with smoke from a fogging machine or similar, then look to see if it leaks out anywhere it shouldn't. I'd try this after the more basic tests, since you'll need to visually inspect a lot of pipe looking for leaks if you run a smoke test. At least some of the pipe you'll need to inspect is likely to be difficult to access.

        Bill

  2. ranson | | #3

    Might be good to check that the plumbers vented everything right. In my current house, the plumbers hooked the vent to the wrong side of the tub trap, so my exhaust fan pulled gas right out of the drain. They also didn't connect up a couple vent pipes in the attic. Had to get them to come back three times to get everything fixed and make my house stop stinking.

  3. ranson | | #5

    So, I don't recall how many years back, but iirc there was imported drywall that gave off corrosive gas when moist. I think it was more than 8 years ago though.

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