What is your limit ?? 29000 ft ? Yeah as you are burning a penny for every 12 inches, the intention should be very much clear - Push as much as you can. But what about the primary fuel - oxygen ? Do you think its available in abundance after 15000 ft ? The obvious answer is NO.The lack of oxygen causes altitude sickness and pulmonary oedema, depression, insomnia, loss of appetite and weight loss leading to the general picture of high altitude deterioration. The cold may cause frostbite, and climbers become dehydrated from lack of water. The liability to snow blindness, respiratory and intestinal problems completes the picture.
Well, this is just the overview, will talk on these issues elaborately later.
