Ignition of iron blocks in a pure oxygen atmosphere is studied using the following model. A heated iron block is exposed suddenly to 100% oxygen atmosphere. Oxidation occurs at the iron block surface, and an iron oxide layer is formed on the surface. Beneath the oxide layer, a melted iron layer exists. Ignition occurs when the melted iron layer flows.
Critical conditions for ignition were calculated. When the initial oxide layer thickness was constant, the maximum surface temperature increased as the initial temperature increased. Ignition occurred when the maximum surface temperature exceeded a critical value of about 1540 K. Ignition occurred also at lower initial temperature, as the initial oxide layer thickness decreased. The conditions were compared with experimental data for ignition of iron cylinders. It was found that the model proposed in this study can accurately describe iron block ignition.