Abstract <p>A mathematical model of radiation-induced transformations in vapor–gas mixtures containing hydrogen, nitrogen, oxygen, and their compounds is presented. In accordance with the array of experimental data used in verification, the model adequately describes the directions and rates of processes in the temperature range from 0 to ~250°C, the pressure from 1 kPa to 0.2 MPa (in some cases up to ~5 MPa), and the absorbed dose rate up to 10³−10⁴ Gy/s over an unlimited time interval. The model can be used as a tool for performing fast calculations with wide sets of external parameters and initial conditions: when assessing the consequences of design and beyond-design-basis accidents at water-cooled nuclear power plants, as well as when substantiating hydrogen explosion safety at facilities with ionizing radiation sources.</p>