Safer Design

A system or operation is considered an inherently safer design if it remains in a nonhazardous state after the occurrence of unacceptable deviations from normal operating conditions. 

Risk is defined as a measure of economic loss, human harm, or environmental harm in terms of both the incident likelihood and the magnitude of the loss or injury. Thus, any effort to reduce the risk arising from the operation of a processing facility can be directed toward reducing the likelihood of incidents (incident frequency), reducing the magnitude of the loss or injury should an incident occur (incident consequences), or some combination of the two. 

In general, the strategy for reducing risk, whether directed toward reducing frequency or consequence of potential accidents, falls into one of the following four categories  

The best time to consider inherently safer design is during the development of new operations and the preliminary design of facilities. Safety can be 

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Trevor A KletZ/ D Sc / Senior Visiting Research Fellow, Depatiment of Chemical Engineering, Loughborough, University U.K. Fellow, American Institute of Chemical Engineers, Royal Academy of Engineers (U.K.), In stitution of Chemical Engineers (U.K.), and Royal Society of Chemlstiy (U.K.). (Inherently Safer Design)... 

PROCESS SAFETY INTRODUCTION INHERENTLY SAFER DESIGN AND OTHER PRINCIPLES... 

Inherently Safer Design Rather than add on equipment to control hazards or to protect people from their consequences, it is better to design user-friendly plants which can withstand human error and equipment failure without serious effects on safety, the environment, output, and efficiency. This part is concerned with this matter. 

Intensification is the preferred route to inherently safer design, as the plants, being smaller, are also cheaper. 

Consider Inherently Safer Design alternatives (e.g., to withstand maximum upset conditions—temperature, pressure, flow)... 

Kletz, T.A. (1998) Process Plants A Handbook of Inherently Safer Design, Taylor and Francis Inc. 

Human factors are an extremely important part of inherently safer concepts. Processes should be designed to avoid error traps. Chapter 6 of this book presents a discussion of human factors as related to inherently safer design. 

Inherently safer strategies can impact the accident process at any of the three stages. The most effective strategies will prevent initiation of the accident. Inherently safer design can also reduce the potential for propagating an accident, or provide an early termination of the accident sequence before there are major impacts on people, property, or the environment. 

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 Role of Inherently Safer Design Concepts in Process Risk Management... 

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. 

These inherently safer design strategies are discussed in more detail in Chapter 3, and examples can also be found in Chapter 4, which discusses inherently safer design opportunities through the life cycle of a chemical process. 

Finally, in considering inherently safer design alternatives, it is essential to remember that there are often, perhaps always, conflicting... 

Figure 2.Z. The relationship/ between ptrocess risk management and inherently safer design strategies.

Chapter 2 introduced four strategies for inherently safer design ... 

The identification of hazards includes both a search for those hazards reduced or eliminated by inherently safer design, and a search for hazards controlled by instmmentation and administrative procedures. 

Additional discussion regarding reactor design strategies is covered in Section 3.1 on minimization (as an inherently safer design strategy), and in Section 4.4 on Design and Construction. 

When dealing with flammable materials, the selection from the inherently safer design options may vary according to the site and process. For example,... 

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. 

The ultimate goal of inherently safer design is elimination of all hazards with no need for controls. However, some control systems are always required. The working logic of a specific control system can make it inherently safer than other alternatives. 

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