(108b) Assessing the Inherent Safety of Substances: Precursors or Hazardous Products in the Loss of Control of Chemical Systems

A fundamental issue of inherent safety during early process development stages is the substitution principle. The selection of reaction pathways involving the use of less hazardous substances or solvents is a central point in achieving inherently safer processes. In this framework, a comprehensive evaluation of the inherent safety of chemical substances results of utmost importance. An extended analysis of substance hazards and stability is needed in order to assess the suitability of the selected process and the advantages of alternative processes. Usually, the hazards of the substances are assessed considering process normal operating conditions. However, it is well known that the loss of control of a chemical process may result in the formation of extremely hazardous compounds due to the unwanted operating conditions caused by the accidental event. Severe accidents were caused in the manufacture of fine chemicals and pharmaceutical products by the release of hazardous decomposition products formed during process "runaway". The problem is well known since the Seveso accident (1976), where relevant quantities of PCDD were formed and released as a consequence of a runaway reaction. In this perspective, avoiding unintended consequences in the selection of alternative processes requires the development of tools for the identification of the possible precursors of hazardous substances in "out of control" conditions. The present study focused on the development and assessment of a comprehensive methodology for the identification of the precursors of hazardous substances. Specific tools were developed. An accident database reporting more than 400 accidents that resulted in the unwanted formation of hazardous substances was implemented. Simplified criteria were developed to identify the precursors of hazardous substances by a preliminary assessment of possible accidental scenarios and reaction pathways. A range of experimental techniques for the simulation of the accidental scenarios of interest were explored in order to obtain reliable and reproducible reference data on the products that may be formed in the loss of control of an industrial chemical process. Critical experimental parameters were identified and reference experimental procedures were proposed for data collection and analysis. In order to assess and critically evaluate the results of the methodology developed in the present study, examples of application to chemical systems of industrial interest are discussed.