The inherent safety of substances in accidental scenarios: a procedure for the assessment of hazards due to decomposition products

The undesired formation of decomposition products in the accidental scenarios that involve the release of chemicals is a core issue in process safety assessment. The secondary substances may be much different from the original ones and, in particular, more dangerous for humans or for the ecosystem. Nevertheless, no robust and widely accepted method exists for the assessment of this kind of hazards. In the present study, an approach to the assessment of this hazard was developed in the more general framework of the analysis of the inherent safety of chemical processes. The toxicological, physical and chemical parameters mostly influencing the hazardous behaviour of a released substance are identified by specific environmental fate models and used in the evaluation of hazard footprints. From these data, hazard indexes are determined, that express in a quantitative way the overall behaviour of a substance with respect to specific categories of hazards (acute toxicity, chronic toxicity and carcinogenicity for humans, ecotoxicity). This allows a comprehensive representation of the hazard profile of a substance. Since the data used for the evaluation of the different parameters are usually scant, a simplified estimation procedure was developed, based on the identification of structure-activity relationships. The application of the described approach to several case studies confirmed the effectiveness of the tool for the comparison of the hazards derived by undesired substance decomposition in accidental scenarios.