[nuancey]

Thanks, that's actually nice to know to this flatlander. Is each climber in a group required to carry O, or just one member? I'd imagine all that survival equipment you guys have to lug up to those very high peaks get awfully heavy the farther up you go.

[schu]

I have only been to about 17K, mostly my experience in the the Cascades/Rainier here in the NW.

O's are normally NOT used by the pros, people often summit Everest without Os. Denali and anything below about 22K do not require Os.

Above about 22K, especially into the "Death Zone" of 8,000M requires Os by novices and guided trips. It takes weeks to acclimatize, normally about 1 day per 1,000 of elevation gain.

Safety gear at that level I suspect is sparse, maybe a first aid kit, some adrenalin shots, food and water.

On Rainier the rule of thumb is each rope team caries a sleeping bag, cook kit and stove, first aid kit and personal gear. There is no enforcement of this, you see all kinds.

schu