Knowledge of material safety properties is essential for safe handling during unit operations, as incidents in plants can often be traced to an insufficient knowledge of the hazardous properties of combustible or flammable substances. If determined carefully and applied properly, safety-related properties will provide information on the reaction behaviors and possible fire and explosion hazards of the specific substance. The aim of this study was to investigate the safety-related properties of o-xylene (e.g., flammability limits, minimum oxygen concentration, maximum explosion overpressure, and flammability zone). These properties were determined with a 20-L-Apparatus at a mixing operation temperature of 150 degreesC and under initial pressures of 760, 1520 mmHg, and 2280 mmHg, respectively. An empirical equation was established from the experimental results for the effects of initial pressure on flammability limit. Potential hazards of unit processes in phthalic anhydride plants are also mentioned. (C) 2002 Elsevier Science Ltd. All rights reserved.