OBGECTIVE: the assessment of admissibility of a human long-term stay in regulated normobaric hypoxic gaseous environments, increasing fire safety of habituated hermoobjects.MATERIALS AND METHODS: Men aged 25–32 (5 people) and 53 (1 person) were surveyed. Inside the test bench a gaseous environment was created with 19–18% vol. oxygen content — a continued stay room, or 17–16% vol.— periodical stay one (4 hours per day). The duration of the tests was 100 days. Once in 10 days there was the «regulation» (fast nitrogen input) of the gaseous environment with the decrease in oxygen concentration up to 15–12% vol., while the volunteers being in such conditions for 2 hours.RESULTS: During the whole period of 100-day sealing none of the volunteers experienced signs of somatic and mental health disorders; all the volunteers completed the testing program successfully.CONCLUSION: The results justify the admissibility of applying the technology of regulated normobaric hypoxic gaseous environments in the developed modes to increase fire safety of habituated hermoobjects, particularly in submarines.