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Currently running Storm King's Thunder, and my players just got the conch of teleportation. During the next session they will be using it. The module says that you take pressure damage for being at the bottom of the sea.

I've looked it up and it seems like most people only count that damage when the players are in the underwater parts. But the entire castle is still at the bottom of the ocean so I'm not sure why being in the underwater part or not would matter.

How did you, as DM, handled this?

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1 Answer 1

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Damage from water pressure only applies to submerged areas.

This is explained in the Maelstrom: General Features section (emphasis mine):

Submerged areas are tinted blue from wall to wall. Characters who can’t breathe underwater must hold their breath in a submerged area. While submerged, they are also susceptible to the effect of water pressure.

The rules given for Water Pressure state emphasis mine):

Creatures and vehicles at Maelstrom’s depth take 7 (2d6) bludgeoning damage per minute from water pressure.

The rules require that you be both underwater and at the Maelstrom's depth to take this damage, and the map denotes these locations by tinting the entire room blue, wall to wall.1

This is close enough to consistent with real world physics.

You take damage while submerged at these depth because of the water pressure. If you aren't under water, there is no water pressure.

Pressure, whether air or water, is the weight of the column of air or water above you. When you are in a sealed underwater structure such as the Maelstrom, the roof of the structure is supporting that weight, so it is exerted on the structure, not on you, when you are inside the structure. To be fair, this isn’t exactly correct, as the maelstrom isn’t a sealed structure, but it’s close enough that for physics-minded people, suspension of belief shouldn’t be any more difficult for this than it is for magic.

I must add, the rules are not an attempt to simulate real world physics, but in this case, they do a decent enough job while keeping the game fun, given my somewhat hand waved explanation in the last paragraph.2


1 To be clear, I have not run Storm King's Thunder, but I have used the rules printed therein to build my own underwater locations.
2 In real life being at a depth of 3000 feet would definitely be fatal, though some theorize that it is possible using helium gas mixtures to prevent the nitrogen narcosis associated with the more common nitrogen-oxygen mixtures used by divers. Only five divers have ever gone below 1000 feet on scuba.

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  • \$\begingroup\$ Thanks! i guess i figured since the castle is submerged that they were underwater no matter what. Makes sense, i was honestly thinking the futurama ep where they go to atlantis in the ship, they themselfs are not submerged but their ship is and they all have to take some medicine plot device to be able to withstand the pressure. \$\endgroup\$
    – Ryan R
    Oct 3, 2020 at 19:52
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    \$\begingroup\$ @RyanR I think it would probably make the whole trip a bit difficult if you were taking bludgeoning damage every minute! If this answer solves your problem, you can mark it with a green check (directly below the vote buttons). \$\endgroup\$ Oct 3, 2020 at 19:54
  • \$\begingroup\$ Yeah for sure, just overthinking it. Thanks again \$\endgroup\$
    – Ryan R
    Oct 3, 2020 at 20:32
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    \$\begingroup\$ You second last paragraph is just plain wrong. If the air is contained entirely in a vessel (like a submarine) then it can be at any pressure you like, usually the pressure when you closed the last hatch. If it’s open to the water (like a diving bell or caisson) then it’s at the same pressure as the water (and will be compressed to a much smaller volume). I’m perfectly happy that, for D&D this doesn’t matter but it certainly did matter for all the 19th century workers who got caisson disease or, as we call it, the bends. \$\endgroup\$
    – Dale M
    Oct 3, 2020 at 21:10
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    \$\begingroup\$ Concur with @DaleM, that paragraph is Just Plain Wrong. I don't experience a change in atmospheric pressure from 14.7 lb/sq in to (near) 0 every time I move from outside to inside my house. Anything can happen with magic, but in the real world, pressure does not change just because there's roof overhead. \$\endgroup\$
    – Novak
    Oct 4, 2020 at 1:50

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