Trifluoroethylene (HFO-1123) and its mixtures are useful as the next generation refrigerants because their global warming potential (GWP) are lower than that of those ordinarily used. HFO-1123, however, has the potential to disproportionate explosively as does tetrafluoroethylene. In this report, the explosive disproportionation of mixed gases of HFO-1123 and other gases were investigated by the fusing of Pt wires ignition method at 10 MPa and 488 K which was the upper limit of the conditions in typical refrigerant usage. It was found that there was a roughly linear correlation between the lower limit of HFO-1123 concentration at which disproportionation occurred and the molar heat capacity at a constant volume of mixed gas. This experimental finding strongly suggests that an explosive disproportionation consists of a thermal explosion process.