Inherently Safer Process Design

We refer to a process that eliminates or minimizes hazards as inherently safer, because the safety basis of the design is inherent in the process chemistry and operations, rather than coming from added safety equipment and procedures. The process designer is challenged to change the process to eliminate hazards, rather than to develop add-on barriers to protect people, the environment, and property. This is best accomplished early in the product and process design cycle, but it is never too late to apply these concepts. This concept is discussed more in detail in the next section. 

There are four major strategies for inherently safer process design [48-50[  

Substitute a less-hazardous substance or process step. 

As mentioned before, scaling-down chemical processes and making them modular is an essential element for a new vision of sustainable industrial chemistry. 

This is also fully in line with the concept of process intensification (see below) and the strategy of minimizing the size of process equipment for a inherently safer process design. 

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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. 

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. 

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

Approaches to inherently safer process design have been categorized in a number of ways. The Center for Chemical Process Safety (5) describes four strategies for inherent safety, derived from Kletz s initial proposals (3,6) ... 

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 ... 

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. 

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) ... 

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... 

There may be well-run facilities in which the operators are doing their best to be careful with facilities or systems that could be redesigned to be inherently safer. These facilities will be inherently safer if designed for operability. Note that inherently safer human factors features can reduce risk of injury to employees (improved personnel safety) and can reduce risk to the process from the worker (improved process safety). 

Error recovery by the operators is only one of several layers of protection to prevent undesired consequences (see Figure 2.1). Process and equipment designs (discussed in previous chapters) that prevent undesired process excursions are inherently safer than designs that require operator intervention. Likewise, designs that enable the operators to intervene before an upset becomes serious are inherently safer than those that do not. 

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. 

Hendershot, D. C. 1991. Design of inherently safer process facilities. Texas Chemical Council Safety Seminar, Session D, Inherently Safe Plant Design, pp. 2-22. 

Designing and Operating Safe Chemical Reaction Processes (HSE 2000). Published by the U.K. Health and Safety Executive and directed to small to medium-sized chemical manufacturing companies using batch and semi-batch processes. It addresses chemical reaction hazards and inherently safer processes, hazards assessment, preventive and protective measures, and management practices. 

Another far more fundamental approach is to reduce the absolute energy released by the reaction. This is achieved in different ways according to the principles of the design of inherently safer processes [1, 4—7]. Kletz, who promoted these ideas, gave some principles to follow for the reduction of severity. 

When a failure or a malfunction occurs, first it needs to be detected. The detection time is influenced by the choice of appropriate alarm settings or by the use of more sophisticated alarm systems, as described in Section 10.4.6. Most important, is choosing the appropriate parameter which must be monitored to detect a malfunction. The design of alarms, interlocks, and control strategies is an important part of process design and should always follow the principles of simplicity in the concept of inherently safer processes (see Section 10.3). 

Safety considerations are an inseparable part of the development of a chemical process and the design and operation of a chemical plant. While risk management and safety features can be added on to a plant design or to an operating plant, safety is most reliably and robustly ensured by developing inherently safer processes. 

Because there is always risk when equipment, instrumentation, and human activity are involved, there is no method of making a plant completely safe. However, facilities can be made inherently safer by careful examination of all aspects of design and management, using modem techniques that are now available. If we are to improve our process safety performance and our public image, inherently safe process design coupled with inherently safe process management is imperative. 

Palaniappan, C., Srinivasan, R. Tan, R., 2002a, Expert system for the design of inherently safer processes. 1. Route selection stage, Ind. Eng. Chem, 41, 26, 6698-6710. 

The search for inherently safer process options must begin early in the process life cycle, and never stop. The greatest potential opportunities for impacting process design occur early in the invention and development of processes. As stated by the National Research Council (Design,... 

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