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Comment by code4tee | Hacker News Reader

Sounds like the building has other more serious plumbing issues. Gasses and odors of any type shouldn’t be able to work their way back into a building via the sewer pipes. The pipes in the building can’t leak and that’s one of the reasons why properly installed drains have traps.

Code inspectors often use the “peppermint test” to test all the above. They dump concentrated peppermint oil into the sewer then go around the building and see if you can smell it. If you can then you have problems with the plumbing.

Buildings having issues likely have bad plumbing and thus their occupants were likely breathing sewer gasses for ages... the “liner fumes” just made all this more obvious.

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> Gasses and odors of any type shouldn’t be able to work their way back into a building via the sewer pipes.

I don't see any claims in the article that the odors entered the building via the sewer pipes. What makes you think that was the path that the odors followed? It could have just as easily been through an open window, or the pipe work could have been near an HVAC intake for the building.

HVAC intake?

I don’t think new air would be introduced unless the system contains an HRV or ERV.

Additionally, this sounds like improper venting, which is a surprisingly common occurrence.

So the gases could be coming up from the drains and toilets.

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?

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.

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.

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?

Not everywhere: https://www.pmmag.com/articles/97318-plastic-pipe-still-limi...

It shouldn’t be possible to pull water out of a p-trap if there is a vent that isn’t blocked.

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.

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.

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.

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.

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"

They say in the article that some of the gasses were coming through the foundation of buildings. It's not just the pipes that are impacted here.

There is mention that the compound used is cured with heat, hot water or steam. This may be relevant as I doubt sewers usually run that hot.

Unless there is actually a build up of high pressure steam being created by this heating it still should be mitigated by a properly plumbed building.

It doesn't take much pressure for steam to bubble past a trap. Pressure on upper floors may build up by buoyancy from below.

What's most likely is a clogged vent pipe, animals get stuck or make nests in there and it effectively defeats the traps.

Though when that happens on an in-use fixture, you’ll hear the gurgling.

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