Introduction. The need to ensure trouble-free operation of inhabited sealed objects of the Navy requires continuous improvement of technologies to increase their fire safety. Such technologies include the creation of hypoxic gas media at facilities that reduce the risk of fires and ensure the possibility of personnel staying in them. The purpose of the work is a comparative assessment of changes in the maximum human working capacity during continuous stay in various normobaric hypoxic environments, promising to increase the fire safety of sealed inhabited objects of the Navy. Materials and methods. In the 1st series of studies, 100 daily sealing of 6 male volunteers (28–53 years old) in controlled hypoxic environments was carried out: [O2] in the premises of permanent residence — 18–19%, periodic (4 hours per day) stay — 16–17%/ In the 2nd series of studies, 6 male volunteers (age 25–51 years) were continuously in argon-containing gas media with [O2]=13,5–14,5%, [Ar]=30–35% for 60 days. During the studies, the dynamics of the mental (operator) and maximum physical working capacity of the subjects were evaluated. Results. Stay in hypoxic environments was accompanied by a decrease in the working capacity of volunteers. The relative degree of negative changes in mental performance in group 1 did not exceed –7%, in group 2 — –10% of the initial level; the maximum decrease in physical performance in group 1 was on average about — –11%, in group 2 — –17% compared with the initial state, which does not go beyond the permissible limits. Conclusion. The introduction of tested gaseous media at naval facilities is promising. The choice of the composition of the gas mixture should be determined by the degree of risk of fires at a particular facility, the technical capabilities of creating and maintaining a hypoxic environment of optimal composition, the number and state of health of the crew.