Inherently strategies

Some of the inherent advantages of the feedback control strategy are as follows regardless of the source or nature of the disturbance, the manipulated variable(s) adjusts to correct for the deviation from the setpoint when the deviation is detected the proper values of the manipulated variables are continually sought to balance the system by a trial-and-error approach no mathematical model of the process is required and the most often used feedback control algorithm (some form of proportional—integral—derivative control) is both robust and versatile. 

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. 

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) ... 

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. 

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

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

The combination of several unit operations into a single piece of equipment can eliminate equipment and simplify a process. There may be inherent safety conflicts resulting from this strategy (see Section 2.4). Combining a number of process operations into a single device increases the complexity of that device, but it also reduces the number of vessels or other pieces of equipment required for the process. Careful evaluation of the options with respect to all hazards is necessary to select the inherently safer overall option. 

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

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. 

Use inherently safer strategies when establishing company design standards, guidelines, or practices. 

The discussion in the following sections is not comprehensive it is intended to provide examples. The inherently safer design strategy (see Section 2.6) used in most of the examples is Simf lify. 

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