Safety Characteristics of Ethylene oxide/Inert gas/Air-Mixtures in Sterilization Processes

Abstract

Part I: Explosion limits of Ethylene oxide/Inert gas/Air-Mixtures Ethylene oxide belongs – like acetylene – to the disintegration capable (chemical unstable) substances. This is the reason that for ethylene/air-mixtures the upper explo-sion limit (decomposition reaction) is 100 vol.-%. For the assessment of explosion hazards by industrial sterilization processes with ethylene oxide (EO), the fl ammability regions of 3-component-systems EO/nitrogen/air, EO/carbon dioxide/air and EO/water vapour/air were determined. The tests were performed at tempera-tures of 20 °C and 100 °C and at pressures of 40 kPa and 100 kPa in accordance with the stan-dard test method EN 1839-B. The observed fl ammability 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 explosion limits of process gases in sterilization processes. Such process gases can consist of EO, nitrogen, carbon dioxide, water vapour and air. The model bases 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 explosion limits of systems with other inert gases or of process gases containing several inert gases. Part II: Maximum Experimental Safe Gap and Defl agration- and Detonation Characteristics of Ethylene oxide/Air-Mixtures For the constructive design of flame arresters the flame proof safe gaps of ethylene oxide/air-mixtures were measured according to IEC 79-1A at atmospheric pressure and 40 °C in de-pendence on the volume content of ethylene oxide. The experimental results show defi nitely that there is besides the M.E.S.G (oxidation reaction) a second minimum (decomposition reac-tion) at a higher ethylene oxide concentration. However, this minimum is above the M.E.S.G. value. In connection with the tests of deflagration flame arresters and detonation flame arresters on their safety against flame transmission the flame propagation velocities and the maximum pressures for ethylene oxide/air-mixtures were determined with the concentration range of the ethylene oxide from 5 to 90 vol.-%. Pipes with an inner diameter of Di = 80 mm and a ratio pipe length/pipe diameter L/D from 185 to 275 were used for the deflagration and detonation tests.