For the assessment of explosion hazards by industrial sterilization processes with ethylene oxide (EO), the flammability regions of 3-component systems EO/nitrogen/air, EO/carbon dioxide/air and EO/water vapor/air were determined. The tests were performed at temperatures of 20 °C and 100 °C and at pressures of 40 kPa and 100 kPa in accordance with the standard test method EN 1839-B.

The observed flammability regions are similar in shape and typical for mixtures with ethylene oxide. According to the molecular heat capacities the regions get larger with nitrogen and smaller with carbon dioxide. They become larger with increasing pressure and increasing temperature.

Using experimental data a semi-empirical model was created that allows the calculation of flammability limits of process gases in sterilization processes. Such process gases can consist of EO, nitrogen, carbon dioxide, water vapor and air.

The model is based on the assumption that the adiabatic flame temperatures along the boundary curves of a flammability region have a certain temperature profile that is nearly independent of the type of the inert gas. The adiabatic flame temperatures were calculated by using the “Gaseq” Code.

Using a temperature profile calculated from only one experimental system EO/inert gas/air it is possible to predict the flammability limits of systems with other inert gases or of process gases containing several inert gases.