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I was wondering the same thing. But do you think it's possible that this process causes backpressure that forces the gases through a trap? Maybe it shouldn't c

I was wondering the same thing. But do you think it's possible that this process causes backpressure that forces the gases through a trap? Maybe it shouldn't cause backpressure if done properly, but maybe some construction companies carelessly block one side of the pipe while it's curing?

code4tee 7y ago
Well if someone wasn’t following procedures then I suppose anything is possible. But the general premise of the article (that ‘fumes’ are making their way back into perfectly good buildings via the plumbing) is problematic.
- ars 7y ago
  Did we read the same article? They never once implied the fumes were entering via the plumbing. In fact I will quote: "Emissions from a nearby CIPP job got indoors through cracks in the building’s foundation and irritated workers to the point that they evacuated"
Enginerrrd 7y ago
I'd suspect it's more likely the opposite: as the pipe is dewatered it creates a negative pressure that pulls the water out of the p-traps which then temporarily allows gaseous exchange with the building air. EDIT: Nevermind, I originally was thinking that a sufficiently negative pressure differential could overwhelm the capacity of the vent. But the more I think about it, the pressure range that I'd expect even with an unusual operation probably wouldn't be far enough outside normal range to do that. ...although there are definitely still some possibilities to do some stupid.
- mikehotel 7y ago
  It shouldn’t be possible to pull water out of a p-trap if there is a vent that isn’t blocked.
  - jcims 7y ago
    If the low pressure is at the vent (e.g. Bernoulli + windy day) the higher ambient air pressure at the drain will push the water through the trap and up the vent pipe. This would only be temporary, but if gases have accumulated near the trap they could diffuse back through the trap and into the room. These would seem to be exceedingly temporary situations however and not likely a source of chronic exposure to pipe gas. The only exception here might be if some HVAC imbalance keeps the ambient pressure in the room at 3-5" of head pressure over the vent.
- hinkley 7y ago
  It's possible. On the top floor of a building I worked at long ago, there was a drain in the floor of the men's bathroom. It had a p-trap but on windy days there was enough vacuum from the vent stack to drain it out. I encountered a neighbor pouring a cup of water into it one day and he explained the problem. I started doing the same, and had to do it every couple weeks during windy periods. But I think that's a problem for the upper floors, both due to fluid dynamics and because the first trap that loses seal would mostly restore equilibrium.
  - perl4ever 7y ago
    My parents' house had a guest room addition with a bathroom which wasn't used for long periods of time, and it became apparent that if the water wasn't run enough it would start to let odors back through the pipes. Anyway, everything uses PVC, right?
    - wahern 7y ago
      Not everywhere: https://www.pmmag.com/articles/97318-plastic-pipe-still-limited-in-plumbing-applications https://www.pmmag.com/articles/97318-plastic-pipe-still-limi...
- taneq 7y ago
  I worked in an office once that had exactly this problem. The sink in the second floor lunch room was fine generally but if you filled it and then pulled the plug, the vacuum behind the water filling the drain pipe was enough to suck the water out of the u-bend and leave the pipe open, after which all of the vapours of Hades issued forth until you ran the tap again for a few seconds.
Bartweiss 7y ago
The liners are apparently being hardened with steam or hot water. That still shouldn't cause backflow, "rising air" isn't worse than diffusion and the little bit of extra pressure from heat should head down-pipe before pushing through traps. But it does sound like a suspect for why this is showing up now in plumbing that hasn't had issues with other smells.

code4tee 7y ago

Well if someone wasn’t following procedures then I suppose anything is possible. But the general premise of the article (that ‘fumes’ are making their way back into perfectly good buildings via the plumbing) is problematic.

ars 7y ago
Did we read the same article? They never once implied the fumes were entering via the plumbing. In fact I will quote: "Emissions from a nearby CIPP job got indoors through cracks in the building’s foundation and irritated workers to the point that they evacuated"

Enginerrrd 7y ago

I'd suspect it's more likely the opposite: as the pipe is dewatered it creates a negative pressure that pulls the water out of the p-traps which then temporarily allows gaseous exchange with the building air. EDIT: Nevermind, I originally was thinking that a sufficiently negative pressure differential could overwhelm the capacity of the vent. But the more I think about it, the pressure range that I'd expect even with an unusual operation probably wouldn't be far enough outside normal range to do that. ...although there are definitely still some possibilities to do some stupid.

mikehotel 7y ago
It shouldn’t be possible to pull water out of a p-trap if there is a vent that isn’t blocked.
- jcims 7y ago
  If the low pressure is at the vent (e.g. Bernoulli + windy day) the higher ambient air pressure at the drain will push the water through the trap and up the vent pipe. This would only be temporary, but if gases have accumulated near the trap they could diffuse back through the trap and into the room. These would seem to be exceedingly temporary situations however and not likely a source of chronic exposure to pipe gas. The only exception here might be if some HVAC imbalance keeps the ambient pressure in the room at 3-5" of head pressure over the vent.
hinkley 7y ago
It's possible. On the top floor of a building I worked at long ago, there was a drain in the floor of the men's bathroom. It had a p-trap but on windy days there was enough vacuum from the vent stack to drain it out. I encountered a neighbor pouring a cup of water into it one day and he explained the problem. I started doing the same, and had to do it every couple weeks during windy periods. But I think that's a problem for the upper floors, both due to fluid dynamics and because the first trap that loses seal would mostly restore equilibrium.
- perl4ever 7y ago
  My parents' house had a guest room addition with a bathroom which wasn't used for long periods of time, and it became apparent that if the water wasn't run enough it would start to let odors back through the pipes. Anyway, everything uses PVC, right?
  - wahern 7y ago
    Not everywhere: https://www.pmmag.com/articles/97318-plastic-pipe-still-limited-in-plumbing-applications https://www.pmmag.com/articles/97318-plastic-pipe-still-limi...
taneq 7y ago
I worked in an office once that had exactly this problem. The sink in the second floor lunch room was fine generally but if you filled it and then pulled the plug, the vacuum behind the water filling the drain pipe was enough to suck the water out of the u-bend and leave the pipe open, after which all of the vapours of Hades issued forth until you ran the tap again for a few seconds.

Bartweiss 7y ago

The liners are apparently being hardened with steam or hot water. That still shouldn't cause backflow, "rising air" isn't worse than diffusion and the little bit of extra pressure from heat should head down-pipe before pushing through traps. But it does sound like a suspect for why this is showing up now in plumbing that hasn't had issues with other smells.