Union Carbide has been investigating the fate and possible hazards of NOx compounds in cryogenic gas separation equipment. It has been learned that trace amounts of NOx in the process streams can accumulate in the equipment under certain conditions. Although mixtures of condensed NOx and condensed hydrocarbons can be ignited with a strong ignition source, the combination does not seem to present an imminent hazard. No explosive NOx-hydrocarbon “gums” have been found yet, but the investigation is still continuing. We recommend that equipment which is exposed to NOx compounds be monitored to detect accumulations and prevent possibly hazardous situations.