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I own a family house that used to until about 20 years ago have a sewage collector pit in use. It has been abandoned for about 20 years now. It has concrete walls and roofing and gravel on the bottom. It was never disinfected or treated in any way.

My question is whether it is safe to go down inside the pit or it could be infectious?

EDIT: My intention is to use it to dispose of plant matter.

EDIT2:

  1. I originally asked this question after I went in because I was afraid it might be infectious (since it was storing human poop for many years before sitting empty for 20). Gases accumulating never occured to me, which was stupid of me, but now I know, since many responses and comments pointed it out. This is something I will take into account and make sure everyone who might ever want to do anything with the pit does too. The pit itself is structurally sound, there is no chance anyone in the next 50 years will ever fall into it by accident or anything like that.

  2. The plant matter too I already put in when I submitted this question, since, as I've written above, it has not occured to me this could pose a danger (that's why my question was originally about the infection risk). So it was a done deed, not an actual decision I took after being aware of the possible issues. A very important additional info is that this 'plant matter' is actually half rotten (as in brown rot) dry wood, it is not something that will vigorously decompose and produce a lot of gases very quickly. Another important aspect is that this pit is safely closed (though it has a grill covered opening with a diameter of about 15 cms on its roof that exits into the garden so it is very definitely not a hermetically closed space) and there is literally no chance anyone ever going inside without taking precautions. I know because it's either me, or someone I might sell the house to, but if I sell it I will most definitely tell them about the pit and the possible accumulation of CO2 and the precautions they need to take. Also, I highly doubt I will ever descend as I really have nothing to do there, I just went down once (before putting anything there and before asking this question) because I was curious and, as it turns out, stupid.

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    "sewage collector pit" is this the same as a septic system? – FreeMan May 4 at 11:55
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    Would be concerned about having enough air to breath in the pit, depending on depth. Have a rope and someone to pull you out. Infection risk is usually for open cuts in skin. Would not be on my top ten places to enter, except for repairing. – crip659 May 4 at 12:05
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    What is your reason for going in the pit? – MonkeyZeus May 4 at 12:10
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    Don't go down there unless you get a confined space blower and vent the pit for 20 minutes first. – JACK May 4 at 12:29
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    It might be properly ventilated for sewage purposes but unless it's properly circulated for breathing purposes then you will die. – MonkeyZeus May 5 at 11:42
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Do not enter the pit.

Without proper ventilation, old septic tanks (and this sounds not enough different to matter) are prone to collect gasses that will kill you (without you noticing. And the people who go in to try and help you, until one is smart enough to use a self-contained breathing apparatus to recover the bodies that died before them.)

It should have been filled with gravel to prevent access (and deaths) when it was decommissioned.

Direct link to top result for septic pits with vegetation killing people.

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    Well, then, the answer linked in the comment above applies precisely to your planned use. Without a blower, it's not ventilated. The one linked there killed 3 people with grass clippings. I've edited to put the link in this answer as well. Debatable if it's really methane as the newspaper claims or just bad reporting (CO2 collects more easily, since it's heavier than air - methane is lighter than air.) – Ecnerwal May 4 at 12:43
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    Also, "plant matter" needs oxygen to decompose. in a mostly sealed bit, you'll create an anaerobic sludge that neither God nor man would ever want to touch. – George Anderson May 4 at 15:30
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    @BenjaminMárkus If you did that, you'd playing with a potential death trap. Drop the idea and fill the pit in. Even if you will always remember to take suitable safety precautions, someone else blundering into it won't know too. Is having a giant compost pit really worth the chance of killing somebody?!?! – Dan Is Fiddling By Firelight May 4 at 21:21
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    @BenjaminMárkus Even if you don't care about your own safety, having a death trap like this on your property is a liability nightmare. You could be held liable for someone else entering it and getting hurt/killed. Until you get this filled in, you should probably also post warning signs of some sort. – bta May 5 at 0:03
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    @BenjaminMárkus Please keep in mind that if you do this wrong, you may kill not only yourself but several of your loved ones. It has happened before and it will happen again. – Tanner Swett May 5 at 12:19

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