Novel Methodology for Inherent Safety Assessment in the Process Design Stage Preeti Gangadharan, † Ravinder Singh, † Fangqin Cheng, ‡ and Helen H. Lou* ,† † Dan F. Smith Department of Chemical Engineering, Lamar University, P.O. Box 10053, Beaumont, Texas 77710, United States ‡ Institute of Resources and Environment Engineering, Shanxi University, Wucheng Road 92, Taiyuan City, 030006 Shanxi, People’s Republic of China * S Supporting Information ABSTRACT: Hazards are intrinsic to a material or its conditions of storage or use [Hendershot, D. C. Inherently safer chemical process design. J. Loss Prev. Process Ind. 1997, 10 (3), 151-157]. Inherently safer designs aim to avoid hazards by design, rather than by add-on measures. The importance of inherent safety has been increasingly stressed in chemical process industries in recent years. It is the most suitable safety approach, particularly in the process design stage. This paper describes a new comprehensive inherent safety index (CISI) for use in the early process design stage. The CISI assigns equipment safety scores to individual units in the process based on chemical, process, and connectivity scores. The chemical score considers the weighted severity score of each chemical in the unit as well as the reactivity score. The reactivity score is calculated separately for the mixture of chemicals in each unit. Since hazards can be compounded by the existence of highly interconnected units, the concept of the connectivity score is introduced. Case studies involving biodiesel and methyl methacrylate processes are used to demonstrate the new safety assessment methodology. The results of the assessment are used to compare the processes based on inherent safety, and they can potentially serve as a valuable aid to clearly identify key areas for improvement in a root-cause analysis. 1. INTRODUCTION Inherently safer design, a philosophy introduced by Kletz, 2-4 focuses on the elimination of hazards or reduction of the mag- nitude of hazards rather than the control of hazards. 5 Since “safety” is a fuzzy concept, it is never possible for a process to be 100% safe. Rather, inherent safety is a relative characteristic, 6,7 and it is most appropriate to describe one process as inherently safer than another. There are a number of process hazards associated with a chemical process. Some examples are high temperature, high pressure, toxicity, reactivity, and explosiveness of chemicals. All these contribute to the relative safety of the process. In order to choose from a number of alternatives, it is essential that the inherent safety be quantified. The Dow Fire & Explosion Hazard Index 8 and the Mond Index 9 are two widely used methods in process industries. These indices are mainly related to the fire and explosion rating of a plant. Another popular method for safety analysis is HAZOP (hazard and operability analysis). 10 HAZOP studies are normally conducted using P&ID (piping and instrumentation diagrams) to find out possible process disturbances and their consequences. However, such details are not available early in the design stage. Over the past few decades, there have been several attempts to quantify the inherent safety of processes in the design stage. 11-17 Some of these make use of fuzzy logic, 13 an expert system called i-Safe, 14 a graphical method, 15 SREST-Layer Assessment, 18 etc. The challenge is to develop a methodology that is not exceedingly complex or time- consuming while at the same time it includes enough detail and depth to provide a realistic idea of the inherent safety. The inherent safety method introduced by Edwards and Lawrence 19 had seven parameters: temperature, pressure, yield, inventory, explosiveness, toxicity, and flammability. These parameters are grouped into two subcategories: process and chemical safety. Scores for each category were given in the range of 1-10. Heikkilä 12 improved upon this index by adding certain new parameters (type of equipment, safety of process structure, chemical interaction, equipment layout) and altered the scoring table to a 0-4 scale. The structure of Heikkilä ’s index is shown in Table 1. In this method, the calculations of the inherent safety Received: November 17, 2012 Revised: February 5, 2013 Accepted: April 4, 2013 Published: April 4, 2013 Table 1. Structure of the Inherent Safety Index 12 symbol score chemical inherent safety index, I CI heat of main reaction I RM 0-4 heat of side reaction, max I RS 0-4 chemical interaction I INT 0-4 flammability I FL 0-4 explosiveness I EX 0-4 toxic exposure I TOX 0-4 corrosiveness I COR 0-2 process inherent safety index, I PI inventory I I 0-5 process temperature I T 0-4 process pressure I P 0-4 equipment safety I EQ inside battery limits ISBL 0-4 outside battery limits OSBL 0-3 safe process structure I ST 0-5 Article pubs.acs.org/IECR © 2013 American Chemical Society 5921 dx.doi.org/10.1021/ie303163y | Ind. Eng. Chem. Res. 2013, 52, 5921-5933