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[Ives]

So, after 13 years my fortress has finally met an ignoble, watery end. Somehow one of the hatches controlling access to the main water reservoir opened on its own volition and flooded a good portion of the living quarters. No idea how that could've happened, because all 4 hatches are linked to the same lever, so an accidental press would've opened the other three (and of course the lever is still in unpressed state), the hatch itself is perfectly intact (and still has the mechanisms inside), so it wasn't deconstructed, and I am not aware of dorfs or other critters being able to open lever-operated hatches.

Here's a picture:


F1 is the ground floor of the reservoir, in the center is the main fortress staircase. You can see the 4 submerged hatches there, the malfunctioning one is circled in red.
F2 is the floor below, mostly occupied by the food stockpile. The four wells are right below the hatches. In case a refill is needed, they can be blocked off by floodgates
F3 is the next floor, - cemetery and living quarters
F4 is the town's water supply, this is just the top portion of it. The stairway in the middle leads down into the caves and there are 4 floodgates around it, in case I need to flush down a forgotten beast, or wash off nasty extracts.

(It's really only a minor design flaw that all relevant levers, including failsafes are in a room BELOW the reservoir, rendering them completely inaccessible in case of a flood. Then again, after accidentally flooding my fortress once before, I really wasn't planning on doing it again!)

I'm stumped. Help me out here guys.

[Absentia]

I'm pretty stumped as well, but I have one thought: You mention that the hatch has "mechanisms" inside. If it was only linked to one lever, it should only have one mechanism. Is it possible you could have inadvertently linked it to something else and triggered that instead?

[Ives]

I'm pretty stumped as well, but I have one thought: You mention that the hatch has "mechanisms" inside. If it was only linked to one lever, it should only have one mechanism. Is it possible you could have inadvertently linked it to something else and triggered that instead?

The game uses the plural of "mechanism", but just to clarify, there's only one inside. The hatch wasn't linked to anything besides the sole control lever (which is still untouched).

[ptb_ptb]

Gremlins can't open mechanism linked hatches can they?

[pisskop]

Maybe you should consider using pressure plates hooked to specially place floodgates in the future, that can close upon flooding.

[Larix]

I can think of two possibilities:
a) the hatch's tile is considered "aboveground" and can freeze. Freezing deconstructs (and hides) hatches.
b) you've got some three-dimensionally mobile creature in or around your reservoir. I've only seen it with flyers so far, but birds can definitely pass through mechanism-operated hatches under some circumstances, opening them.

[Ives]

I can think of two possibilities:
a) the hatch's tile is considered "aboveground" and can freeze. Freezing deconstructs (and hides) hatches.
b) you've got some three-dimensionally mobile creature in or around your reservoir. I've only seen it with flyers so far, but birds can definitely pass through mechanism-operated hatches under some circumstances, opening them.

The entire reservoir is subterranean (and filled via a pump), and either way the hatch is intact, just open. Plus it's a temperate biome that for some reason never freezes.

Now, the point about creatures being able to pass through mechanism operated hatches (or at least open them) sounds promising. I haven't seen any inside reservoir though, of course the resulting flood would've washed them out. It might've been a bugbat or something.

One other thing. I have 2 restless haunts floating about in my fortress, which I kept for style points (one of them has been following my goblin king for the past 5 years, and I've figured he needed someone to talk to besides the crundles and giant grasshoppers he's training). I don't suppose ghosts can open mechanism-operated passages? Man, if that's the case, I totally deserved this!

[Tacomagic]

I can think of two possibilities:
a) the hatch's tile is considered "aboveground" and can freeze. Freezing deconstructs (and hides) hatches.
b) you've got some three-dimensionally mobile creature in or around your reservoir. I've only seen it with flyers so far, but birds can definitely pass through mechanism-operated hatches under some circumstances, opening them.

The entire reservoir is subterranean (and filled via a pump), and either way the hatch is intact, just open. Plus it's a temperate biome that for some reason never freezes.

Now, the point about creatures being able to pass through mechanism operated hatches (or at least open them) sounds promising. I haven't seen any inside reservoir though, of course the resulting flood would've washed them out. It might've been a bugbat or something.

One other thing. I have 2 restless haunts floating about in my fortress, which I kept for style points (one of them has been following my goblin king for the past 5 years, and I've figured he needed someone to talk to besides the crundles and giant grasshoppers he's training). I don't suppose ghosts can open mechanism-operated passages? Man, if that's the case, I totally deserved this!

I think this might be your issue.  From the wiki:

Ghosts can open doors, even forbidden ones (leaving them unlocked).

I'm assuming hatch-covers count as doors for the purpose of this flood.

[Ives]

Ghosts can open doors, even forbidden ones (leaving them unlocked).

I'm assuming hatch-covers count as doors for the purpose of this flood.

Yeah, that's probably what happened then. I guess the ghost passed through the hatch tile, opening it, and of course it didn't close because it was linked to a lever. Vucar Udarmeng wasn't a friendly ghost at all 

Though it's pretty impressive that he managed to lift a hundred pounds of reinforced steel without a body. May be he just wanted to make more ghosts?

[Quietust]

I think this might be your issue.  From the wiki:

Ghosts can open doors, even forbidden ones (leaving them unlocked).

I'm assuming hatch-covers count as doors for the purpose of this flood.

It would apply to hatch covers, but it should not apply to mechanism-controlled ones. "Forbidden" doors only include ones you've manually locked and can be unlocked by kobolds and gremlins (and seemingly also ghosts), but once you link them to a lever, I'm pretty sure nothing can open or close them aside from the mechanism.

[Tacomagic]

I think this might be your issue.  From the wiki:

Ghosts can open doors, even forbidden ones (leaving them unlocked).

I'm assuming hatch-covers count as doors for the purpose of this flood.

It would apply to hatch covers, but it should not apply to mechanism-controlled ones. "Forbidden" doors only include ones you've manually locked and can be unlocked by kobolds and gremlins (and seemingly also ghosts), but once you link them to a lever, I'm pretty sure nothing can open or close them aside from the mechanism.

As we have a conflicting witness account from larix that indicates that some wild animals (posibly only fliers) pass through a mechanically sealed doors, this might be worth some investigation to see if there's be a bug here.  Especially if the intended function is for mechanisms to completely seal an area.

I think ghosts count as fliersto some extent (have to crack one open and check its flags), so if there is a bug, they may be affected.

Think I'll create a little test fort when I get home tonight. Should be a simple thing to test.  Create a chamber with a lot of doors and with a ceiling made out of a checkerboard of sealed hatches and then use DFHack to teleport any birds on the map into that chamber.  Then, see if they can escape.

[Nikow]

Try make it in easier way, retire some fort with laver linked hatch, go to it in adventure mode, fly up, then when you are under hatch just fly upward in some side (not straight up). It should left hatch open...

[Ives]

I've done a little test and lo and behold, ghosts can indeed open mechanism-locked passageways with (at least in my case) hilariously tragic consequences.



B - basement area for the living and their corporeally-challenged friends
G - ground floor where terrible deeds have been wrought in the name of !!SCIENCE!!
F1 - the floor directly above the sacrificial pit, 7 copper hatches gleaming in the thin winter sunlight. All 7 are linked to the lever below. Note that one of them is open (DUN DUN DUN)
F2 - I've been meaning to fill this with water, but the test has run successfully before the surrounding ponds thawed

I've put this up on the bug tracker thingy.