Inherently safer process

CCPS G-41. Inherently Safer Processes A Life Cycle Approach. American Institute of Chemical Engineers, Center for Chemical Process Safety, New York. 

Process safety is fundamental to the basic practice of chemical engineering thus, the concepts of inherently safer processes should be instilled in chemical engineering students at an early stage. Practicing engineers should be encouraged to adopt the concepts. 

Inherently safer processes provide an opportunity to reduce or eliminate many of these long term economic costs. These benefits will not be realized unless we recognize and fully account for the long term costs associated with hazardous materials and processes. 

Inherently safer design is a fundamentally different way of thinking about the design of chemical processes and plants. It focuses on the elimination or reduction of the hazards, rather than on management and control. This approach should result in safer and more robust processes, and it is likely that these inherently safer processes will also be more economical in the long run (Kletz, 1984, 1991b). 

Design strategies which result in an inherently safer design may also tend to improve process economics. For example, minimizing the size of equipment or simplifying a process by eliminating equipment will usually reduce capital investment and reduce operating costs. However, overall process economics are very complex and are impacted by many factors, and it may not always be true that an inherently safer process is also economically more attractive. 

An inherently safer process offers greater safety potential, often at a lower cost. However, selection of an inherently safer technology does not guarantee that the actual implementation of that technology will result in a safer operation than an alternate process which is inherently safer. The traditional strategy of providing layers of protection for an inherently more hazardous process can be quite effective, although the expenditure of resources to install and maintain the layers of protection... 

Approaches to the design of inherently safer processes and plants have been grouped into four major strategies by IChemE and IPSG (1995) and Kletz (1984, 1991b) ... 

Basic process chemistry using less hazardous materials and chemical reactions offers the greatest potential for improving inherent safety in the chemical industry. Alternate chemistry may use less hazardous raw material or intermediates, reduced inventories of hazardous materials, or less severe processing conditions. Identification of catalysts to enhance reaction selectivity or to allow desired reactions to be carried out at a lower temperature or pressure is often a key to development of inherently safer chemical synthesis routes. Some specific examples of innovations in process chemistry which result in inherently safer processes include ... 

A United States Environmental Protection Agency report (Lin et al., 1994) contains an extensive review of inherently safer process chemistry options which have been discussed in the literature. This report includes chemistry options which have been investigated in the laboratory, as well as some which have advanced to pilot plant and even to production scale. 

This chapter describes the four main design strategies for development of inherently safer processes ... 

Many of the inherently safer design aspects discussed here appear in Guidelines for Safe Automation of Chemical Processes (CCPS, 1993b). It makes excellent reading for greater depth and treatment of inherently safer/process control concepts. 

Design and development of inherently safer process chemistry and physical treatment may be the most economical way to eliminate a... 

Sandoz (Ankers, 1995) has developed a software tool to assist chemists and engineers in identifying hazards, and inherently safer process options. 

The following checklist contains a number of questions which can aid in identifying inherently safer process options. The list is adapted from CCPS (1993a). Other checklists, particularly the extensive checklist in Appendix B of the Guidelines for Hazard Evaluation Procedures, 2nd Edition with Worked Examjzles (CCPS, 1992) contain many questions which are related to inherent safety. 

Appendix A Sample Inherently Safer Process Checklist... 

Althaus, V. E., and S. Mahalingam (1992). Inherently Safer Process Designs. South Texas Section AIChE Process Plant Safety Symposium, February 18-19, 1992, Houston, TX, ed. W. F. Early, V. H. Edwards, and E. A. Waltz, 546-555. Houston, TX American Institute of Chemical Engineers South Texas Section. 

Ankers, R. (1995). Introducing Inherently Safer Concepts Early in Process Development With PRORA. CCPS Inherently Safer Process Workshop, May 17, 1995, Chicago, IL. 

Carrithers, G. W., A. M. Dowell, and D. C. Hendershot (1996). It s Never Too Late for Inherent Safety. International Conference and Workshop on Process Safety Management and Inherently Safer Processes, October 8-11,1996, Orlando, PL, New York American Institute of Chemical Engineers. 

Hendershot, D. C. (1995a). Conflicts and Decisions in the Search for Inherently Safer Process Options. Process Safety Progress 14,1 (January), 52-56. 

The Institution of Chemical Engineers (IChemE), and The International Process Safety Group (IPSG) (1995). Inherently Safer Process Design. Rugby, England The Institution of Chemical Engineers. 

International Conference and Workshop on Process Safety Management and Inherently Safer Processes (1996). New York American Institute of Chemical Engineers. 

Inherently Safer Chemical Processes—A Life Cycle Approach was written by the Center for Chemical Process Safety Inherently Safer Processes Subcommittee ... 

The major approach to inherently safer process designs is divided into the following categories ... 

The intent of this Guidelines book is to provide the principles for the evaluation of chemical reactivity and for use of this information to design and operate safer chemical plant processes. Special emphasis is placed on the use of state-of-the-art methodology in the areas of theory, testing methods, and applications in design and operation of inherently safer processes. 

A new approach for computerized Inherent Safety Index is also presented. The index is used for the synthesis of inherently safer processes by using the index as a fitness function in the optimization of the process structure by an algorithm that is based on the combination of an genetic algorithm and case-based reasoning. Two case studies on the synthesis of inherently safer processes are given in the end. 

The calculations of the Inherent Safety Index (ISI) are made on the basis of the worst situation. The approach of the worst case describes the most risky situation that can appear. A low index value represents an inherently safer process. In the calculations the greatest sum of flammability, explosiveness and toxic exposure subindices is used. For inventory and process temperature and pressure the maximum expected values are used. The worst possible interaction between chemical substances or pieces of equipment and the worst process structure give the values of these subindices. 

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