Water Pressure

[ChaosArchon]

Hey so I wanted to know if there are any core rules regarding what happens if alot of water suddenly is released on top of your character. Like say the party is in a glass dome underwater thats relatively shallow in the sense that you still get sunlight and your cleric casts shatter on the dome and then water-breathing and water walk on the party to make sure nobody drowns and we all float up to the surface at 60ft per round if I remember correctly. Does the party survive the impact of the water crashing in? or is it ocean falls and everybody dies (oh what a death).

[Slipperychicken]

I believe Stormwrack has rules for this.

[ChaosArchon]

Care to share for someone without the splatbook in question?

[Alex12]

The water pressure rules don't kick in until you get at least 100 feet down, at which point you have to make Fort saves (DC 15, +1 per each prior check) or take 1d6 damage per 100 feet deep each minute. Aquatic subtype ignores the first 500 feet, and reduces damage to 1d6 every 200 feet below that instead.
Also, some deep-adapted creatures like whales or water elementals are completely immune to this damage.
For the actual water impact, I suggest you check out the falling rules in the SRD.
"For each 200 pounds of an object’s weight, the object deals 1d6 points of damage, provided it falls at least 10 feet. Distance also comes into play, adding an additional 1d6 points of damage for every 10-foot increment it falls beyond the first (to a maximum of 20d6 points of damage)."
Water is roughly 62 pounds per cubic foot. A 5x5x5 cube of water is 125 cubic feet of water (though presumably not all of this is hitting the character). That said, the impact would be extremely nasty.

EDIT: if you're shallow enough to see the sun reasonably clearly, the Light rules in Stormwrack are also useful. 30 feet or less is brightly illuminated out to 100 feet, shadowy out to 200. 31-60 feet deep is brightly lit out to 60 feet and shadowy out to double that, 61-120 feet deep halves the previous distances, 121-180 drops them by another 1/3rd, and 181-300 cuts it down by half again, so it's bright out to just 10 feet, and shadowy 20 feet beyond that. Low-light vision doubles vision distances at all depths.

[ChaosArchon]

The water pressure rules don't kick in until you get at least 100 feet down, at which point you have to make Fort saves (DC 15, +1 per each prior check) or take 1d6 damage per 100 feet deep each minute. Aquatic subtype ignores the first 500 feet, and reduces damage to 1d6 every 200 feet below that instead.
Also, some deep-adapted creatures like whales or water elementals are completely immune to this damage.
For the actual water impact, I suggest you check out the falling rules in the SRD.
"For each 200 pounds of an object’s weight, the object deals 1d6 points of damage, provided it falls at least 10 feet. Distance also comes into play, adding an additional 1d6 points of damage for every 10-foot increment it falls beyond the first (to a maximum of 20d6 points of damage)."
Water is roughly 62 pounds per cubic foot. A 5x5x5 cube of water is 125 cubic feet of water (though presumably not all of this is hitting the character). That said, the impact would be extremely nasty.
So what you're saying is that if said cleric decides to do this, ocean falls everyone dies -.- (we're level 6, i have 30hp).

[Alex12]

So what you're saying is that if said cleric decides to do this, ocean falls everyone dies -.- (we're level 6, i have 30hp).

If you were a 5x5 square character (ensuring that all the water hit you), and had a 5x5x5 block of water fall on you from a height of 10 feet, by my calculations, you'd take about 77d6 damage. So don't do that.

[ChaosArchon]

Yeah is there a way to minimize the impact damage... like a featherfall for the ocean :P

[Alex12]

Yeah is there a way to minimize the impact damage... like a featherfall for the ocean :P

Well, the obvious solution is to not drop oceans on yourself.

You could also make the argument that the falling damage rules should apply, and treat it like you falling into the water, rather than the other way around. Rules for that are in the SRD.
http://www.d20srd.org/srd/environment.htm#fallingObjects

You could also treat it like being in the bury zone of a cave-in. http://www.d20srd.org/srd/dungeons.htm#caveInsAndCollapsesCr8

[ChaosArchon]

Well yeah the obvious solution is to not shatter the glass but thats alot less entertaining. Thank you very much for the info though!

[Mellack]

As I read shatter, there is no way the spell will destroy the entire dome all at once. They will put a hole in it, if do anything at all. So as long as they don't make that hole directly over the characters, the city would fill up over some time. I would also assume anyone who builds a city underwater would also have means of plugging such a hole.

[Slipperychicken]

If you were a 5x5 square character (ensuring that all the water hit you), and had a 5x5x5 block of water fall on you from a height of 10 feet, by my calculations, you'd take about 77d6 damage. So don't do that.

Rules Compendium caps the total fall damage at 20d6, not just from distance. Which is stupid IMO, but whatever. You also get a DC 15 reflex save to dodge falling objects.

Also, unless you're some kind of Ooze, you (hopefully) aren't a 5x5 cube.

[Flickerdart]

As I read shatter, there is no way the spell will destroy the entire dome all at once. They will put a hole in it, if do anything at all. So as long as they don't make that hole directly over the characters, the city would fill up over some time. I would also assume anyone who builds a city underwater would also have means of plugging such a hole.
Unless your hole jeopardizes the structural integrity of the glass, which collapses under the pressure of the water - exactly the sort of thing that happens to a breached dam, I might add.

[andromax]

D&D doesn't really cover the explosive decompression aspect of the scenario you are envisioning.

Take the Decanter of Endless Water as an example of how to treat it if there is a hole that is broken into the glass dome.

" ....."Geyser" produces a 20-foot-long, 1-foot-wide stream at 30 gallons per round.

The geyser effect causes considerable back pressure, requiring the holder to make a DC 12 Strength check to avoid being knocked down. The force of the geyser deals 1d4 points of damage but can only affect one target per round. The command word must be spoken to stop it."

I would probably scale that up a bit depending on depth and hole size.

[Alex12]

Rules Compendium caps the total fall damage at 20d6, not just from distance. Which is stupid IMO, but whatever. You also get a DC 15 reflex save to dodge falling objects.

Also, unless you're some kind of Ooze, you (hopefully) aren't a 5x5 cube.

That is dumb, yes. But I'll point out that, in the SRD, there's a description of a dropping ceiling trap (it's one of the CR-9 traps) that doesn't give a reflex save. That one deals 12d6 damage.
I've always found that, in a situation where you're doing something the DM doesn't know how to adjudicate, having at least one option of "this is a similar situation found in the rules" is appreciated.

I also wanted to figure out the maximum amount of damage for a normal character. The 5x5 cube thing was just to simplify the math.

[Zombimode]

As I read shatter, there is no way the spell will destroy the entire dome all at once. They will put a hole in it, if do anything at all. So as long as they don't make that hole directly over the characters, the city would fill up over some time. I would also assume anyone who builds a city underwater would also have means of plugging such a hole.

I was about to point out Ultima 9 as a counterexample, but then I remembered the immortal words of Colonel Jack O'Neil "Ok, bad example".