Low pressure effects
In such high altitudes of the terrestrial atmosphere the air pressure drops to dangerous values, resulting in acute mountain sickness (AMS) and high altitude pulmonary edema (HAPE).
Oxygen reduction for fire prevention
The terrestrial atmosphere contains 21% oxygen, which is the value that human beings have adapted to during a long evolution process. But there is some tolerance. Under normal air pressure persons can live and work with down to 13% oxygen. The danger of fire is much lower in a low oxygen air. With 15% oxygen even paper can no longer burn with a flame. 
- What air pressure, combined with different oxygen levels, is required for persons to survive?
- What air pressure, combined with different oxygen levels, is required for persons to live and work?
- What are the results from the Biosphere 2 experiment? Ideas for mitigation and/or compensation?
- What is known about the behaviour of dusty air under low gravity?