COMMENT:Diving at altitude is exciting and a challenge many divers enjoy. At high elevations above sea level the ambient air pressure upon a lake is less than one atmosphere. The means the pressure differences when a diver ascends are greater than if a diver were to make the same ascent from the same depth in the sea. Accordingly, altitude diving requires specialist training, excellent buoyancy control and adjustments to the No Decompression Limit for any particular depth. Many dive computers automatically adjust for lower ambient pressure experienced at high altitude but not all do, so it pays to check the user manual when planning a dive in a mountain lake. Even if no mishaps occur and no warnings are given by a diver's personal dive computer, high altitude divers should employ additional conservative measures such as maintain normal hydration, use nitrox whenever possible, avoiding or reducing repetitive diving, using an ascent line to slowly ascend hand-over-hand, and avoid or reduce strenuous work both in the water and after the dive.
When diving at altitude it is also prudent to have adequate oxygen on hand to last the journey to the nearest Emergency Department, in this case 1.5-2 hours away.
~ Peter Buzzacott, MPH, PhD