Underwater Pressure and Objects and Constructs


Rules Questions


So I'm playing a wyrwood fighter for Hell's Rebels and noticed the city was along the shore and the potential for seafaring adventures, especially with the player's guide mentioning aquatic sorcerer bloodline and aquatic elves.

Naturally I'm wondering about the wyrwood's advantages for such a situation. With the construct traits, I'd obviously don't have to worry about breathing underwater, however underwater pressure which seems pretty extreme for most parties/creatures.

Construct Traits, Relevant Items Bolded:
•No Constitution score. Any DCs or other statistics that rely on a Constitution score treat a construct as having a score of 10 (no bonus or penalty).
•Low-light vision.
Darkvision 60 feet.
•Immunity to all mind-affecting effects (charms, compulsions, morale effects, patterns, and phantasms).
•Immunity to bleed, disease, death effects, necromancy effects, paralysis, poison, sleep effects, and stunning.
•Cannot heal damage on its own, but often can be repaired via exposure to a certain kind of effect (see the creature's description for details) or through the use of the Craft Construct feat. Constructs can also be healed through spells such as make whole. A construct with the fast healing special quality still benefits from that quality.
Not subject to ability damage, ability drain, fatigue, exhaustion, energy drain, or nonlethal damage.
Immunity to any effect that requires a Fortitude save (unless the effect also works on objects, or is harmless).
•Not at risk of death from massive damage. Immediately destroyed when reduced to 0 hit points or less.
•A construct cannot be raised or resurrected.
•A construct is hard to destroy, and gains bonus hit points based on size, as shown on the following table. (OMITTED)
•Proficient with its natural weapons only, unless generally humanoid in form, in which case proficient with any weapon mentioned in its entry.
•Proficient with no armor.
•Constructs do not breathe, eat, or sleep.

PRD - Environment - Water Dangers wrote:
Very deep water is not only generally pitch black, posing a navigational hazard, but worse, deals water pressure damage of 1d6 points per minute for every 100 feet the character is below the surface. A successful Fortitude save (DC 15, +1 for each previous check) means the diver takes no damage in that minute. Very cold water deals 1d6 points of nonlethal damage from hypothermia per minute of exposure.

Obviously for most of the very deep underwater rules, constructs are fine with darkvision and immunity to nonlethal damage. For the pressure damage, though, the only trait that might be relevant is, "Immunity to any effect that requires a Fortitude save (unless the effect also works on objects, or is harmless)."

The question of the day: Are objects and constructs susceptible to underwater pressure damage?

I can't find it in the PRD rules anywhere, and don't feel comfortable looking through adventure paths to see if there's any outside-the-core-rules detailing such anywhere, but if anyone has any insight or can cite anything, that would be great.

Looking through Archives of Nethys, I think I found one reference, but I'm not sure it's really definitive: the Submerge Ship spell states it "protects the ship and all aboard from the dangers of drowning and pressure", which suggests the ship, being an object, would need the spell to avoid pressure damage. However this being a spell from an AP (it popped up in the search for "pressure"!) I'm not sure how accurate it is under the rules.

Logically I'd assume hollow objects would suffer the pressure damage; not like one finds a lot of intact ships under the sea. But a lot of smaller non-hollow objects are found A-OK (besides the rust), and plenty of adventures or scenarios with creatures adapted to underwater pressure are fine:

Game Mastery Guide - Fast-Play Ship Combat wrote:
Natural Adaptation: Any creature that has the aquatic subtype can breathe water easily and is unaffected by water temperature extremes that are found in that creature's typical environment. Aquatic creatures and creatures with the hold breath ability are much more resistant to pressure damage; they do not suffer damage from pressure unless they are moved instantaneously from one depth to another in the blink of an eye (in which case they adapt to the pressure change after successfully making five successive Fortitude saves against the pressure effects).

Without their equipment breaking for being several hundred feet underwater for several hours and with their gear and loot intact.


Most objects underwater have a hardness high enough to deal with the 1d6 pressure damage, but, as you go deeper, it does weed out the more brittle things, unless they've been adapted to that pressure, ie, using native creature shells for armour/weapons, etc.

In theory, at 200ft down, it's 2d6/min, which could pose a problem for steel weapons, but things like adamantine are totally fine, as in most magically enchanted stuff, due to the increase in hardness from magic.

Worst case scenario, you have a +5 adamantine something, it's got a hardness of 30, meaning it would be in danger of starting to take damage (it would have a pretty big hp pool) at around 6d6, or 600ft down, that's pretty deep. And considering the hp of the item, it would take a while for it to reach broken, let alone destroyed.


So objects (and constructs) would have to make fortitude saves against pressure damage, and the hardness (well DR for the constructs) is usually high enough that it'd have to be pretty deep for it to be an actual worry.

Sure that works for me. Now just gotta find ways to protect against pressure damage. Game Mastery Guide suggests that "Pressure damage can be avoided entirely with effects such as freedom of movement" but I hope I can find some more cost effective ways than a ring of freedom of movement (40K in an AP seems crazy high).


You are way over planning this. I don't think I have ever seen the water pressure rules used, and even if they are, if an AP is going to have you go that deep there is going to be some mechanism to get the party there and let them function (or you will be high enough level that it is trivial.)

At the very worst, you would need a few points of healing every few minutes, something fairly easily managed.


Dave Justus wrote:

You are way over planning this. I don't think I have ever seen the water pressure rules used, and even if they are, if an AP is going to have you go that deep there is going to be some mechanism to get the party there and let them function (or you will be high enough level that it is trivial.)

At the very worst, you would need a few points of healing every few minutes, something fairly easily managed.

I tend to over plan everything, true. But this is mostly a thought exercise when I came upon the hypothetical situation where I do wanna know if objects/constructs take pressure damage for future situations such as when combating or my characters defending against such situations.

I've been scrounging up rules and forum posts for underwater pressure for the last few days and there is VERY little discussion on it besides some very old comments by James Jacobs about by the core rules not very much would survive deep underwater, and having to introduce some rules down the line (I guess the GMG) for stuff to help with that.

Also since playing a wyrwood character, I'm trying to manage expected damage accordingly since actual healing for a construct is rather annoying and I'm trying to not be too much of a burden/tax on party resources.


pressure damage to things are caused by a pressure differential. A solid object with no compressable air in it will be fine. Its when you have say a sub or person with air in their lungs at a lower pressure, that the imbalance causes damage as the structure tries to support the pressure trying to equalize. The same is true in space, except in the opposite direction (high pressure inside, low pressure outside).


Pathfinder Adventure Path, Lost Omens, Rulebook, Starfinder Roleplaying Game Subscriber

To answer the question:

No.

Characters take damage which may be negated with a fortitude save (creatures in area, fortitude negates, to use spell terminology).
An object is not a character.
An object does not take the damage, and therefore doesn't need to make the save.
A construct only needs to make fortitude saves if an object would.


Protoman wrote:

So objects (and constructs) would have to make fortitude saves against pressure damage, and the hardness (well DR for the constructs) is usually high enough that it'd have to be pretty deep for it to be an actual worry.

Sure that works for me. Now just gotta find ways to protect against pressure damage. Game Mastery Guide suggests that "Pressure damage can be avoided entirely with effects such as freedom of movement" but I hope I can find some more cost effective ways than a ring of freedom of movement (40K in an AP seems crazy high).

The "such as" seems to grant a little wiggle room. I would think that items that use Freedom of Movement in their construction and which grant the same ability to move underwater without hindrance might work. I would ask your GM about the Pearl of the Sirines and the Scavenger's Ring.


Chemlak wrote:

To answer the question:

No.

Characters take damage which may be negated with a fortitude save (creatures in area, fortitude negates, to use spell terminology).
An object is not a character.
An object does not take the damage, and therefore doesn't need to make the save.
A construct only needs to make fortitude saves if an object would.

Do you know if that's stated anywhere an object doesn't take damage? The deep water rules does say "character" and "diver", is that enough for "it didn't state objects also, so it doesn't affect them"?


Randall Rapp wrote:
pressure damage to things are caused by a pressure differential. A solid object with no compressable air in it will be fine. Its when you have say a sub or person with air in their lungs at a lower pressure, that the imbalance causes damage as the structure tries to support the pressure trying to equalize. The same is true in space, except in the opposite direction (high pressure inside, low pressure outside).

Ah so with such a case the Submerge Ship spell would be needed to protect the ship because it's compressable.


Forget my earlier advice. At only 2,000 gp this is what you want.

Archives of Nethys wrote:

Vest of the Deep

A vest of the deep creates a constant shell of magical energy that protects the wearer from extreme environmental pressure, such as that inflicted by water at a depth of over 100 feet. It does not provide any protection from constriction or other forms of direct crushing damage, nor does it grant water breathing.


Gisher wrote:

Forget my earlier advice. At only 2,000 gp this is what you want.

Archives of Nethys wrote:

Vest of the Deep

A vest of the deep creates a constant shell of magical energy that protects the wearer from extreme environmental pressure, such as that inflicted by water at a depth of over 100 feet. It does not provide any protection from constriction or other forms of direct crushing damage, nor does it grant water breathing.

Ooo that does look useful! Thanks, Gisher!


James Jacobs was the only Paizo person I could find that even mentioned underwater pressure issues anywhere I could find in the forums, and was was kind enough to offer his opinion on the matter

James Jacobs wrote:
I'd say that as a general rule, objects (and thus constructs) are not subject to pressure damage. I'd go further to say that incorporeal creatures or most undead would be immune as well. I'd ACTUALLY like to classify pressure damage as "bludgeoning damage that affects living creatures or objects with enclosed hollow spaces." But in the interim, it's best to simply use common sense on a case by case basis. After all, it's not like we made up the concept of pressure damage from deep water. It's a real-world thing. A rock dropped into the ocean won't get crushed. And there's plenty of real-world examples of deep-sea robots that work down there—so constructs being immune to it is neat too. And furthermore, the idea that a zombie or other undead could just walk down to the bottom of the ocean and not worry too much about it makes undead more interesting as well.

While not an official ruling, it's definitely a great piece insight for anyone hoping to do any sea-faring campaigns.


Protoman wrote:
Gisher wrote:

Forget my earlier advice. At only 2,000 gp this is what you want.

Archives of Nethys wrote:

Vest of the Deep

A vest of the deep creates a constant shell of magical energy that protects the wearer from extreme environmental pressure, such as that inflicted by water at a depth of over 100 feet. It does not provide any protection from constriction or other forms of direct crushing damage, nor does it grant water breathing.

Ooo that does look useful! Thanks, Gisher!

You're welcome. I came across it by accident and immediately thought of this thread. It's PFS legal if that matters to you.


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Gisher wrote:
Protoman wrote:
Gisher wrote:

Forget my earlier advice. At only 2,000 gp this is what you want.

Archives of Nethys wrote:

Vest of the Deep

A vest of the deep creates a constant shell of magical energy that protects the wearer from extreme environmental pressure, such as that inflicted by water at a depth of over 100 feet. It does not provide any protection from constriction or other forms of direct crushing damage, nor does it grant water breathing.

Ooo that does look useful! Thanks, Gisher!
You're welcome. I came across it by accident and immediately thought of this thread. It's PFS legal if that matters to you.

....it definitely does now that you mention it! First time a scenario comes up where I gotta go past 100 ft underwater, investing 2000 gp on the vest! After buying the AP issue and never actually reading it, of course!


Here is the PRD link for the pressure damage.

The construct trait "Immunity to any effect that requires a Fortitude save (unless the effect also works on objects, or is harmless)." may apply since it is a Fort save.

I don't think it is covered, so this is how I would treat it:
What is the construct's main component?
Crush-able: flesh, wood
Non-Crush-able: stone, metal

Changed my mind.

A simpler alternative is to have the construct be affected, but to apply the hardness of the construct. This would have the less crush-able ones take less damage because they are harder.

/cevah


Slightly off-topic but nonetheless highly relevant. The pressure damage is absolute bull. In real life many thousands of people scuba dive to that depth and beyond with no ill effects and breath-hold free diving to that depth is not uncommon by spearfishermen.

Breathing underwater (i.e. breathing pressurised air) and ascending quickly could well kill or seriously injure you though - it's a condition known as the bends. But breathing underwater also equalises the pressure so there are no practical depth limits.

For free-divers this article is useful. Suggesting the limit is 400 feet, but really the limit on staying underwater would be the amount of time the character can hold their breath.


^Even that article has some problems: While having your lungs (and other air-filled body cavities) collapsed by sudden application of pressure would be destructive, it is possible to survive with collapsed lungs as long as you have some other way getting oxygen -- we know this because every baby has to do this before it is born, and has to inflate its lungs for the first time when it is born (and premature infants have problems in part because they lack the surfactant that keeps the lungs from partially sticking back to themselves after exhaling, thus forcing them to expend extra effort to re-inflate their lungs with every breath).

Things that get you at depth are oxygen toxicity (for air, can begin atseveral atmospheres, but nitrogen narcosis usually gets you first), nitrogen narcosis (starts at a few atmospheres), high pressure nervous syndrome (starts at over 10 atmospheres, and can be partially suppressed by nitrogen narcosis, but not completely counteracted), and microtubule depolymerization (starts at upper hundreds to thousands of atmospheres). None of these phenomena would bother most objects or Constructs, as long as they do not have hollow air spaces in them.

For most of the above, Wikipedia has the information; for microtubule depolymerization, Google for "pressure microtubule depolymerization", and some of the first few articles (excluding the ones about myocardial pressure) have useful information (note 1 bar = 0.1 megapascal = 100 kilopascal = approximately 1 atmosphere = 14.7 psi = pressure generated by approximately 30 feet of water).

Extremely high pressure can cause changes in non-organic materials even in the absence of interior hollow spaces, but this requires depths much greater than the Marianas Trench, so a Construct going into the depths of a normal ocean is unlikely to have to worry about them.

Note that if a rigid object or Construct (or for that matter a living creature) contains interior hollow spaces that cannot be equalized with the outside pressure in a controlled manner, all bets based upon the above are off. Submarines have been destroyed by taking them to depths beyond their limits (see USS Thresher (SSN-593, which fell below maximum depth due to a series of mechanical failures).

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