The paper presents the estimation of sealed-off fire states in underground coalmines. The estimation is based on the analysis of gas samples taken from the sealed-off fire areas in coalmines. Considering the mining-geological factors influencing on fire state estimation, the authors suggested their own method for analyzing and estimating sealed-off fire states by so-called “fire characteristic”, which graphically describes tendencies of five components of fire gas – oxygen, nitrogen, carbon dioxide, carbon monoxide and hydrocarbons – in time. The analysis of fire gas components tendencies in time and their correlation allows to draw out proper conclusions about fire state estimation. In order to mark fire indicators tendencies in time the authors applied the time series analysis. The cases studied confirmed, that the suggested method is beneficial in the analysis and estimation of fire state in sealed-off areas.