If you have no air to breathe, you can hold your breath for 2 rounds per point of Constitution, but only if you do nothing other than take move actions, free actions, swift actions, and immediate actions. If you take a standard action or a full-round action while holding your breath, the remaining time you can hold your breath is reduced by 1 round. When you can hold your breath no longer, you must succeed on a DC 10 Constitution check to continue holding your breath. The check must be repeated each round, with the DC increasing by 1 for each previous success. When you fail one of these Constitution checks, you begin to suffocate. In the fi rst round, you fall unconscious (0 hit points). In the following round, you drop to –1 hit points and are dying. In the third round, you suffocate and die (–10 hit points).
prepararsi per resistere di più:
As a move action, you can prepare yourself for a long period of being under water with some careful breathing. On a successful DC 15 Swim check,
you can add 4 to the number of rounds you could otherwise hold your breath, provided you start to hold your breath immediately after making the check.
soffocamento lento:
Spoiler:
A Medium creature can breathe easily for 6 hours in a sealed chamber measuring 10 feet on a side. After that time, the
creature takes 1d6 points of nonlethal damage every 15 minutes. Each additional Medium creature or significant
fire source (a torch, for example) proportionally reduces the time the air lasts. When a creature falls unconscious
from this nonlethal damage, it drops to –1 hit point and is dying. In the next round, it suffocates and dies (–10
hit points). Smaller creatures need half as much air per size category smaller, and larger creatures
need four times as much air per ize category larger. A larger volume of air lasts for a longer time. So, for instance, if two humans and
a gnome are in a sealed chamber measuring 20 feet by 20 feet by 10 feet, and they have a torch, the air lasts for almost 7 hours (6
hours/3.5 people and torches × 4 10-ft. cubes = 6.86 hours).
spero sia chiaro ()
fonte: rules compendium pag 141