The purpose of this work was to obtain data on explosive limits for ethylene oxide (EtO) in nitrogen beyond the published data range. Tests were conducted at temperatures from 60°-190°C and pressures in the range 10 to 80 psig. Initial measurements showed that the limits for the EtO/N2 system are unusually dependent on the details of the ignition source. Hot wire ignition gave very erratic responses. Induction coil sparks were not satisfactory due to inadequate energy and uncertain gap breakdown at elevated pressure. However, high-energy capacitive discharge across an exploding bridge element tuned to the ignitive process gave responses that were reproducible and judged to be true and conservative. Graphite filament was used as the exploding bridge “wire” to avoid contamination of the test mixture. (Carbon is a product of EtO explosions.)
The data from this study show the EtO explosive range becomes wider with increasing pressure at the low end of the temperature range examined than previously understood from literature data. At modest pressures, the directly-measured limits at elevated temperature agree with extrapolations of earlier reported data. Because of the pressure nonlinearity, the system is deemed safer at 80 psig and high temperature than had been predicted from the linear treatment.