Operation of atmosphere detritiation systems during fire in confinement sector with tritium inventory at risk presents a concern for catalytic reactor to operate in thermally unstable regime. Catalytic oxidation of organic compounds commonly released during fire occurs through reactions with high heat effect and can cause uncontrollable increasing temperature in reactor. Under certain conditions self-ignition of fume gas will start and continue in regime of gas-phase reaction at very high temperature with flame propagating in direction opposite to gas flow. As a result, catalytic reactor loses its operability and presents an intrinsic hazard for atmosphere detritiation system. This study assesses the impact of various parameters, such as heat effect, rate and activation energy of catalytic chemical reaction, and concentration of hydrocarbons on probability of catalytic reactor falling into thermally unstable regime. Experimental tests with catalytic oxidation of fume gases produced by combustion of polymeric insulation materials of electrical cables confirmed results of the assessment and allowed to identify conditions for catalytic reactor to operate in thermally unstable regime. To mitigate the probability of such event, arrangement for catalytic reactors in atmosphere detritiation system shall be changed. Various options are reviewed.