Based on the test results obtained in a spherical pressure chamber, the inerting concentration of halohydrocarbons C2F4Br2, CF3Br, and C2F5H was experimentally determined in a stoichiometric methane–air mixture, depending on the ignition-source energy. A wire burnt by electric current or a pyrotechnical composition was used as an ignition source. The energy of ignition sources was varied within 2 to 420 J. To obtain the real value of the inerting concentration of halohydrocarbons, independent of the ignition source used, the energy of the latter should be higher than 100 J for C2F4Br2 and C2F5H and 400 J for CF3Br. Application of ignition sources with lower energy yields underrated results and is related to the growth of the minimum ignition energy with addition of halohydrocarbons rather than to inerting of the combustible mixture.