Extreme Altitude (20,001 to 26,000 feet)
At extreme altitude, creatures are subject to the altitude fatigue and altitude sickness of lower altitudes. Mundane acclimation to high altitudes no longer benefits climbers at this height. When an individual takes any ability damage from altitude sickness while at extreme altitude, he develops a hacking cough within 2d4 hours. This results in a persistent cough as the cold, arid air dries out the individual’s throat and lungs. The coughing spasms are frequent and cause a –4 penalty on all Acrobatics checks made to balance, Climb checks, Perception checks made to listen, and Stealth checks. In addition, any spell with verbal components requires a concentration check (DC 15 + spell level) to successfully cast. If this check is fails, the spell is not lost, but the caster must start over again in the next round if he wishes to cast it.
These coughing spasms can be so violent that they can even break ribs. Each day an individual suffers the cough, he takes 1d6 points of damage. Moving back to a lower altitude zone relieves the cough, as does 2 hours per day spent in an extremely humid environment (such as a fog cloud). Spells such as heal and restoration can remove this effect but do not prevent it from returning normally. The cough is not a disease, and cannot be cured by remove disease.
Death Zone (More than 26,000 feet)
Normal life is not possible above an altitude of 26,000 feet; there simply is not sufficient atmospheric pressure to allow enough oxygen to be inhaled by breathing creatures. When a creature that does not possess the Altitude Affinity feat, or does not fall into one of the types or subtypes immune to high altitude effects, climbs to 26,000 feet of elevation, it immediately begins to suffocate. Acclimation to high altitudes does not prevent this effect.
Section 15: Copyright Notice
Section 15 here.