Abstract
Oxygen enrichment of room air has proved to be valuable for people who need to work at altitudes of 4000 m and above. In this study the feasibility of using the same technique in ski and other mountain resorts at the lower altitudes of 2500 to 4000 m is considered. While many people find these altitudes invigorating, some are distressed by the hypoxia, especially at night. The analysis shows that all resorts up to an altitude of 3250 m (10,600 ft) can have the equivalent altitude reduced to 1000 m (3280 ft) by oxygen enrichment without incurring a fire hazard. (The equivalent altitude is that which provides the same inspired P(O2) during air-breathing.) Even resorts as high as 4250 m can have the equivalent altitude safely reduced to 1500 m, that is,  a lower altitude than Denver, Colorado. This application of oxygen enrichment is likely to be most valuable for improving sleep and assisting in the initial acclimatization process.

High Alt Med Biol. 2002 Spring;3(1):59-64.

https://pubmed.ncbi.nlm.nih.gov/12006165/

“Room oxygen enrichment improves sleep and subsequent day-time performance at high altitude”

Abstract

We carried out a randomized, double-blind trial at 3800 m altitude to test if a small degree of room oxygen enrichment at night improves the quality of sleeps, as well as performance and well-being the following day. Eighteen sea-level residents drove from sea level to 3800 m in one day and then slept one night in ambient air, and another night in 24% oxygen, the order is randomized. With oxygen enrichment, the subjects had fewer apneas (P < 0.01) and spent less time in periodic breathing with apneas (P < 0.01) than when they slept in ambient air. Subjective assessments of sleep quality were also significantly improved. The morning after oxygen-enriched sleep there was a lower acute mountain sickness score (P < 0.01) and a greater increase in arterial oxygen saturation from evening to morning (P < 0.05). The larger increases in arterial oxygen saturation from evening to morning suggest that the control of breathing may have been altered. Based on this research, installing an oxygen-enriched room system at high altitude is relatively simple and inexpensive, and it also shows promise for improving the well-being of both travelers and residents.

Respir Physiol. 1998 Sep;113(3):247-58.

https://pubmed.ncbi.nlm.nih.gov/9840334/