Dear Tom,
I’m going mountain climbing in the Rocky Mountains soon. What is the highest that one can go and not need specialized breathing equipment?
Richard Mallorn, Lincolnwood

Dear Richard,
The onset of breathing problems with increasing elevation is known as acute mountain sickness, or AMS. The percentage of oxygen in the air is about 21 percent and it remains relatively unchanged up to about seven thousand feet. The lack of oxygen causes AMS, but ascending slowly and avoiding strenuous activity is the best way to avoid it. AMS affect about 20 percent of people at 8,000 feet and 40 percent at 10,000 feet. The percentage increases to practically 100 percent of people by the time one ascends to 16,000 feet.