Breathing (OSS)

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Breathing presents the greatest obstacle to long-term underwater adventuring, and even to short-term underwater survival. Unless characters are native to watery depths, they must find some means of staying submerged for extended periods of time without drowning.
For most campaigns, magic provides the key to underwater survival. Characters can use magic spells and devices, from potions of water breathing to airy water spells, which enable them to exist and adventure in an underwater setting.
In low-magic campaigns, or adventures where such magic spells and items are not readily available, Dungeon Masters can offer "naturally" occurring plants, such as oxygen-supplying seaweeds, minerals, or other objects as a way of solving the underwater breathing dilemma. Alternatively, some technologically minded individual or group could provide PCs with the means to survive underwater through the aid of experimental breathing equipment (primitive oxygen tanks).
In any event, adventurers who do not have some method of breathing underwater must resort to the last- ditch solution of holding their breaths. Rules for holding one's breath, as well as drowning, can be found in Chapter 14 of the Player's Handbook.
==Types of Magical Breathing==
As mentioned above, the ability to breathe through magical means can come about in a variety of ways. Potions, rings, helms, and other items, as well as spells, allow surface-dwelling player characters access to mysterious underwater realms.
However, these magical items accomplish this task using a variety of eldritch methods. In turn, each item's particular dweomer interacts differently with the complex forces at work underwater-including water pressure and water resistance and affects important actions such as movement and combat.
Magical breathing falls into three general categories: conversion, transformation, and adaptation. Magical items and spells are arranged in these categories based on the way in which their magic accomplishes its purpose. DMS should use these categories as guidelines when determining the effects of new or rare magical items on underwater survival and adventuring.
===Conversion===
Magical items and spells that use alteration magic to effect a subtle change in the environment around the caster or wielder fall in this category. For example, the magical power of a helm of underwater action converts water to breathable air. Conversion dweomers allow the caster or wielder to speak while underwater- though other creatures outside the influence of the magical item or spell may not clearly understand the speaker.
In addition, conversion dweomers automatically compensate for changes in pressure. The breathable atmosphere generated by these spells and items gradually matches the pressure of the surrounding water, thereby completely protecting users from the negative effects of pressure-including spells such as rapture of the deep. However, these dweomers do not protect the user against the ravages of cold temperatures (see Temperature section of this chapter).
Airy Water: This spell magically changes a volume of normal liquid into a foamy, breathable substance. The sphere or hemisphere the spell creates does not float, but rather slowly sinks until it comes to rest against a solid surface. Those creatures inside an airy water sphere can freely speak with and understand creatures outside the sphere provided everyone involved uses the same language.
Additionally, anyone engaging in combat inside the sphere does not suffer any negative effects associated with underwater combat. Thus, no underwater movement and combat penalties apply.
Helm of Underwater Action: This magical item converts a quantity of water into a bubble of air that surrounds the wearer's head and enables him to breathe normally while underwater. In addition, the magical item grants the wearer exceptional underwater vision at least five times greater than normal for an average player character. The wearer's hearing also improves (see Table 42: Underwater Hearing Ranges for details).
The helm does not nullify the effects of water resistance. Thus, the wearer of the misnamed helm of underwater action still suffers all of the movement and combat penalties associated with underwater adventuring.
===Transformation===
Magical items and spells that fall into this category utilize alteration magic to effect a change within the user or wielder that allows him to survive in the surrounding environment. For example, a potion of water breathing does not change water into air, but rather allows its user to extract oxygen from the water.
Unlike conversion dweomers, transformation dweomers do not usually surround the wielder with a bubble of perfectly pressurized atmosphere. Thus, their users are typically subject to the full effects of pressure and other related dangers.
Water Breathing: Both the wizard and clerical versions of this spell transform the recipient's body so that it can extract oxygen from the surrounding water. The recipient's lungs and vocal chords fill with water, thereby cutting off the possibility of speech, including spellcasting. In fact, if a recipient of a water breathing spell returns to dry land or wanders into an airy water sphere, he must spend one round clearing the water from his lungs before he can speak or cast spells with verbal components.
Although the recipients of this spell can breathe water, they still cannot function smoothly underwater. All attack and movement penalties still apply to creatures under the influence of a water breathing spell.
Potion of Water Breathing: This item works in exactly the same way as the water breathing spell.
Polymorph Self/Other: These wizard spells can completely transform a surface-dwelling creature into a water-breathing one. This transformation completely protects the recipient/caster from all negative effects associated with pressure and temperature while the recipient is in marine form. In addition, the polymorph other spell allows the recipient to attack without penalties and hear as a marine creature while in marine form.
Both spells negate any underwater movement penalties incurred from pressure and water resistance.
===Adaptation===
Items and spells in this category use enchantment/charm magic to facilitate complete adaptation to a hostile environment. Adaptation dweomers often grant total immunity to specific negative effects associated with environmental conditions such as movement penalties, attack penalties, temperature penalties, and pressure- related afflictions.
Ioun Stone (Iridescent): Unlike conversion and transformation dweomers, the power of the stone does not serve a biological function. Rather, the enchantment of the ioun stone grants its user complete independence from the biological necessity of breathing. However, the stone's power does not allow the user to speak without air. Nor does its power extend to movement through a medium. Users still suffer penalties to their movement rates and attack rolls from water pressure, water resistance, and temperature.
Necklace of Adaptation: This magical item protects the wearer from harmful gases by removing his dependence on breathing. However, the wearer must still breathe air in order to speak. The adaptation dweomer completely protects the wearer from the effects of pressure, but not movement and combat penalties.