Inherently safer design approaches

Many organizations are revisiting their chemical processes to determine whether inherently safer design approaches can help them reduce or remove certain hazards and associated risks from their facilities. In other cases, new technology and advances in management science may allow a company to test or permanently... 

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). 

The concept of inherently safer plant has been with us now for many years. But in spite of its clear potential benefits related to safety, health and the environment (SHE), as well as the costs, there has been few applications in chemical plant design. But as Kletz (1996) has written there are hurdles to be overcome. Inherently safer design requires a basic change in approach. Instead of assuming e.g. that we can keep large quantities of hazardous materials under control we have to try and remove them. Changes in belief and the corresponding actions do not come easily. 

An inherently safer design eliminates or minimizes hazards by changing process conditions or process chemistry, and by selecting appropriate locations for hazardous operations. Inherently safer design includes the following approaches ... 

In certain cases, such as changes created by a significant expansion, it is better to have a small group of specialists first identify the potential hazards and seek our inherently safer designs prior to any type of committee review. Brief descriptions of various approaches to hazard identification are presented in Appendix B to this chapter. 

The concept of inherently safer design was first proposed by Kletz, who developed a set of specific design principles for the chemical industry [92] (see also [50]), but it has been publicized and promoted later by many technologists from petrochemical and chemical companies such as Dow, Rohm and Haas, ExxonMobil, and many others. A relevant source of information is the book Inherently Safer Chemical Processes A Life Cycle Approach [49]. 

Inherently safer design includes the following strategies and approaches ... 

The basic concept of inherently safer process design is to reduce the hazard of a process by reducing or eiiminating the hazards associated with materials and operation of the process. This approach is described in detaii in the CCPS book, Inherently Safer Chemical Processes, A Lifecycle Approach, 2nd edition, 2008. in brief, there are four major strategies for inherently safer design ... 

The principle ways of designing inherently safer plants and other ways or makiug plants user-friendly are summarized as follows, with examples (Kletz, Plant De.sign for Safety—A U.ser-Friendly Approach, Hemisphere, 1991). 

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) ... 

A database of the hazards associated with different types of equipment and unit operations including the applicability of inherently safer technology in each. As innovative solutions to hazards in equipment and process operations are discovered these could be included in this database for use by others in reducing risk in similar equipment and processes. A summary of design approaches for a number of common types of chemical process equipment will be published in CCPS (1997). This summary may be a starting point for the development of this database. 

Mansfield, D. P. (1994). Inherently Safer Approaches to Plant Design. Warrington, Cheshire, U. K. United Kingdom Atomic Energy Authority. 

My book Plant Design for Safety—A User-Friendly Approach [1] and References 12-15 describe many examples of ways in which plants can be made inherently safer. Note that we use the term inherently safer, not inherently safe, as we cannot avoid every hazard. 

In general, the safety of a process relies on multiple layers of protection. The first layer of protection is the process design features. Subsequent layers include control systems, interlocks, safety shutdown systems, protective systems, alarms, and emergency response plans. Inherent safety is a part of all layers of protection however, it is especially directed toward process design features. The best approach to prevent accidents is to add process design features to prevent hazardous situations. An inherently safer plant is more tolerant of operator errors and abnormal conditions. 

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

The essence of the inherently safer approach to plant design is the avoidance of hazards rather than their control by added-on protective equipment (Kletz 1998). It particularly emphasizes eliminating large inventories of hazardous materials where feasible. 

Procedural controls, process controls, 98-99 Process controls, 96-100 active controls, 98 inherently safer approach, 97 mitigation techniques, 99 passive controls, 97-98 procedural controls, 98-99 safe operating limits, 99-100 Process definition, documentation, 102-104 Process design, documentation, 105 Process hazard analysis (PHA) risk assessment, 92-93 screening methods, 63 Process risk management decisions, documentation, 105-106... 

This chapter provides the fundamentals of design for passive and active fire protection systems. A passive system should be used wherever possible, as this is an inherently safer approach than an active system. 

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