Comparison of safety indexes for chemical processes under uncertainty

Abstract

The fatal consequences of industrial incidents have made evident the need for suitable tools to develop inherently safer process designs. Traditionally, in a process design project, the evaluation of safety aspects is left for analysis after the detailed design has been completed. This approach leads to the use of control loops, barriers and protection layers as the only ways to prevent incidents and to reduce the possible outcomes. An alternative to this approach is the application of the concept of inherent safety, which was introduced to set up several principles that aim to enhance process safety by eliminating, avoiding or minimizing sources of risk. In this work, we present a comparison of different safety metrics in their role to evaluate the risk associated with a given process design. The indices selected for consideration are better applied at the conceptual stage of the process design, and they were the Dow's fire and explosion index (F&EI), the fire and explosion damage index (FEDI), the process route index (PRI) and the process stream index (PSI). All these indices use different input information and their outcomes have different rankings. The metrics were applied to an ethylene production process to identify risk levels, and the location of streams and pieces of equipment that pose the highest risk within the process. An evaluation of the indices in their capability to track design changes in operating conditions aiming to improve the safety level of the process was developed. To perform the assessment of the safety metrics in a more extensive manner, an uncertainty analysis based on a Monte Carlo simulation framework was implemented and compared to the traditional use of single-value design variables. Within this context, an insightful assessment of uncertainty's effect on process safety characteristics was achieved because of the identification of ranges of safetyrelevant performance outcomes (zones of risks and opportunities) that can be probabilistically characterized. The approach was applied to a case study related to the production of ethylene from shale gas. The results showed how some indexes are better suited to capture the risk characteristics associated with the process when changes in the operating conditions of the section with highest risk were implemented. The methodology can be extended to other processes of interest, and may serve as a basis for the safety and process design community to propose adjustments in the structure of the safety indices based on a better understanding of their performance and reliability as part of the efforts towards the continued improvement of those safety metrics.

An Integrated Approach to the Design of Centralized and Decentralized Biorefineries with Environmental, Safety, and Economic Objectives

“…The decision makers should balance these conflicting objectives and select a strategy that reconciles the importance of the economic, environmental, and safety objectives. Alternatively, the decision makers may use an economic platform to incorporate sustainability, risk, and resilience into the ROI calculations [57][58][59][60][61][62].…”

“…Inclusion of multiple environmental metrics-while the case study in this paper focused on GHG emissions, other environmental metrics may be used, such as land use change, water usage and discharge, pollutant discharge, acidification, and eutrophication; • Consideration of additional objectives such as resilience [57], reliability, availability, and maintainability [62]; • Integration of centralized and decentralized biorefineries with other infrastructures through the concept of industrial symbiosis [63,64]; • Consideration of feedstock variability and uncertainty [60,65].…”

Multi-objective optimisation for safe multi-floor process plant layout using the Dow’s Fire & Explosion Index

“…It is common practice that safety analysis, and the layout configuration, of chemical process plants are carried out after the detailed design of such plants are completed (Ortiz-Espinoza et al, 2021). This leaves little or no room for design modifications to improve on the overall safety levels of the plant which can lead to fatal consequences, disruption of production activities, and irreparable losses to the plant and neighbouring environment (Ejeh et al, 2021).…”

“…However, studies have also shown that the layout configuration of such process plants directly and indirectly contribute to about 79% of accidents (Kidam and Hurme, 2012). It then becomes important not just to develop suitable tools for safer process designs (Ortiz-Espinoza et al, 2021), but further extend such tools to obtain safer layout configurations as well. Roy et al (2016) presented a review of safety indices applicable to process design where brief descriptions of 25 representative indices were given with their level of application and inputs required.…”

“…From such data, the F&EI is calculated as a product of the Material Factor (MF) and the process unit hazards factor (F 3 ) and is helpful in determining the degree of hazard (Table 1) a process unit poses in the plant. The chemical properties of the material(s) within a process equipment is quantified by the MF, and the process unit hazards factor is the result of the product of the general (F 1 ) and special (F 2 ) process hazards factors (American Institute of Chemical Engineers, 1994, Gupta et al, 2003, Ortiz-Espinoza et al, 2021. Patsiatzis et al (2004) gives a detailed procedure for the calculation of each of these factors.…”