What is the maximum achievable altitude without a pressure suit?
39,000 ft is the maximum limit for 100% oxygen, without leaks, and a perfect mask. One can then “pressure breath” where the lungs are inflated above ambient pressure, which keeps pressure in the lungs at 39,000 feet. You must force the air out to exhale–it gets to be a lot of work eventually. I have spent a couple hours at 43,000 feet in the old days in USAF fighters with poorly operating pressurization systems. Such high altitudes without a pressure suit also invite the “bends”. In extreme necessity one can go to about 46,000 feet for a few minutes, but hypoxia ensues, and 10 minutes is about the limit. Exhaling is very hard and tiring. The oxygen mask is painfully tight, and must be precisely fitted. It is common to blow a lot of air back out through the tear ducts, which make your eyes water. Then if your masochistic nature takes over, you can put on a “pressure jerkin”– a heavy shirt lined with a bladder that inflates. This will counter the internal pressure in the lungs and make
