Plant inherently safer

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). 

The following should be considered in designing an inherently safer plant involving reactor systems ... 

Figure 12-40. Process A Batch reaction with all reactants added at the beginning of the reaction. There is a considerable amount of flammable and hazardous material in the reactor at the beginning. (Source S. M. England, Inherently Safer Plants Practical Applications," Process Safety Progress, Vol. 14, No. 1, pp. 63-70, AlChE, 1995.)...

Kletz repeated the Jubilee Lecture twice in early 1978, and it was subsequently published (Kletz, 1978). In 1985 Kletz brought the concept of inherent safety to North America. His paper, Inherently Safer Plants (Kletz, 1985), won the Bill Doyle Award for the best... 

Some Key Questions and Decisions Related to Inherently Safer Plant Design (Rogers et al., 1995)... 

Siting, both location and layout, is critical for inherently safer plants. Evaluate siting with respect to the risk imposed by the process on the population, environment, adjacent facilities, and community. These evaluations apply to small revisions as well as major new processes. 

The Design of Inherently Safer Plants (1988). Chemical Engineering Progress (September), 21. 

Englund, S. M. (1993). Process and Design Options for Inherently Safer Plants. Prevention and Control of Accidental Releases of Hazardous Gases, ed. V. M. Fthenakis, 9-62. New York Van Nostrand Reinhold. 

Kletz, T. A. (1985). Inherently Safer Plants. Plant/Of>erations Progress 4, 3 (July), 164-67. 

Englund, S. M. (1994). Inherently Safer Plants—Practical Applications. American Institute of Chemical Engineers i 994 Summer National Meeting, August 14-17,1994, Denver, CO, Paper No. 47b. 

Kletz, T. A. (1991). "Inherently Safer Plants—Recent Progress. IChemE Symposium Series No. 124, 225-33. 

The view is therefore growing that we should try to design plants so that they are safe even if there is a fault in the software. This can be done by adding on independent safety systems, such as relief valves and hardwired trips and interlocks, or by designing inherently safer plants that remove the hazards instead of controlling them (see Chapter 21). 

An inherently safe plant1112 relies on chemistry and physics to prevent accidents rather than on control systems, interlocks, redundancy, and special operating procedures to prevent accidents. Inherently safer plants are tolerant of errors and are often the most cost effective. A process that does not require complex safety interlocks and elaborate procedures is simpler, easier to operate, and more reliable. Smaller equipment, operated at less severe temperatures and pressures, has lower capital and operating costs. 

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 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. 

The conceptual design phase is the most critical when designing inherently safer plants, since the alternative process concepts are created and analyzed in this phase. This emphasizes the need to introduce safety evaluation tools into the preliminary process design. Time and money is saved when fewer expensive safety modifications are needed during the later stages of design. 

Hendershot, D. C. 1994. Conflicts and Decisions in the Search for Inherently Safer Process Options. AIChE Summer National Meeting, Denver, CO. Inherent Safer Plants Symposium, August 16, 1994. 

A far more realistic goal is the inherently safer plant. Such a plant is designed to assure that it can be operated safely and so as to minimize the effects of any accidents which do occur. The object is to design a plant which can be safe the people who will operate and maintain it largely determine whether it will be safe. 

Design techniques for an inherently safer plant include improved layouts, inventory reduction, and process improvements. 

In summary, the inherently safer plant is user-friendly. Its design takes maximum advantage of the accumulated experience of the chemical industry and takes into consideration the fact that people must operate and maintain it. It is built so that opportunities for plant and people failures are minimized, so that the effects of those failures which do occur are minimized, and so that the effects of failures can be mitigated readily through adequate facilities and access for emergency response. 

The need to design inherently safer plants has been expanded to encompass designing evironmentally acceptable plants. Environmentally acceptable plants generate minimum quantities of potentially hazardous wastes either as potential emissions to the environment or as materials requiring disposal. Wastes are recycled and reused where possible. If this is not possible, they may be treated to reduce or eliminate the hazard or destroyed through incineration. Disposal in a secure landfill is the final option. 

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