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. 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.
Pressure, whether air or water, is the weight of the column of air or water above you. If you aren't under water, there is no water pressure. You take damage while submerged at these depth because of the water pressure. 1 This is close enough to consistent with real world physics. 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. The rules given for Water Pressure state emphasis mine):Ĭreatures and vehicles at Maelstrom’s depth take 7 (2d6) bludgeoning damage per minute from water pressure. While submerged, they are also susceptible to the effect of water pressure. Characters who can’t breathe underwater must hold their breath in a submerged area.
Submerged areas are tinted blue from wall to wall. This is explained in the Maelstrom: General Features section (emphasis mine): Damage from water pressure only applies to submerged areas.