Retention of extinguishing gas (N-2 or N-2-Ar mixsts.) was studied under lab. conditions (a chamber 0.72 m(3) with leaks) and under real conditions (a room 700 m(3) with openings and leaks). The retention time increased with increasing the d. of the extinguishing gas to the air d. An uniform distribution of the O-2 concn. was then achieved.