The boiling point of water changes with changing altitudes, but most recipes are based on the assumption that the cook will be cooking at sea level. Cooks at higher altitudes need to make certain adjustments, and this is especially true with pressure cooking.
The Boiling Point of Water
As elevation increases, the temperature at which water boils decreases. At sea level, the boiling point of water is 212 degrees Fahrenheit. On top of Pike's Peak (14,000 feet above sea level), however, the boiling point is about 187 degrees. For every 540 feet of altitude increase, the boiling point decreases by about 1 degree.
Pressure cookers work quickly and efficiently by increasing the pressure on liquids, which increases the boiling point of water. (For a more thorough explanation of pressure cooking science, see 4 Reasons to Use a Pressure Cooker.) So cooks at elevations above sea level don't benefit as fully from pressure cooking's wonder-working, time-saving efficiency. Pressure cooking will still save time, energy and money, but here's the high-altitude rule:
For every 1,000 feet above 2,000-foot elevation, you must increase cooking time by 5 percent.
So if your pressure cooker recipe indicates that you should cook something at high pressure for 25 minutes and you live at 6,000 feet above sea level, you should actually keep cooking at high pressure for 30 minutes.