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4 The Concepts of Inherently Safer Processes and Assessment
Pages 59-82

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From page 59...
... and describes the role of ISPs in a process safety management (PSM) system as background for the analysis of the decisions made during those developments.
From page 60...
... The terms "inherently safer processes" (ISPs) ,1 and variations such as "inherently safer technology" (IST)
From page 61...
... A process with reduced hazards is described as inherently safer compared to a process with only passive, active, and procedural controls. An inher­ ently safer process should not, however, be considered ‘inherently safe' or ‘absolutely safe.' While implementing inherent safety concepts will move a process in the direction of reduced risk, it will not remove all risks.
From page 62...
... process safety management standard (OSHA, 29 CFR 1910.119)
From page 63...
... Someone's attenuate may be someone else's moderate. You may wish to consider segregate as a measure 4 As with the terminology regarding inherent safety categories, these classifications fall along a spectrum of process safety approaches, and people may disagree about the category into which a particular design falls.
From page 64...
... These have been summarized and adapted from the 2008 publication Inherently Safer Chemical Processes: A Life Cycle Approach, 2nd Edition from the AIChE Center for Chemical Process Safety, and similar definitions can be found in many reference texts on process safety. Passive Passive safety systems are those that control hazards with process or equip ment design features without additional, active functioning of any device.
From page 65...
... For example, one can describe a process alternative as inherently safer with respect to the acute toxicity of a particular raw material when compared with another alternative. This state ment does not say anything about the relative inherent safety characteristics of the two processes with respect to other hazards (fire, explosion, reactive chemis try, chronic toxicity, environmental impact, etc.)
From page 66...
... There is potential synergy between process simulation and understanding ISP characteristics of a process. Process simulation is a mathematical representation of industrial chemical processes, often used in process design, control, and optimiza tion.
From page 67...
... The results of any analysis, however, have to be considered in context. For example, as already described, the inherent safety of one hazard may be reduced and another increased depending on size of a shipment or the mode of transportation of the shipment, or risk may shift from one community well equipped to respond to an emergency to one less able to do so.
From page 68...
... The first of these is integration of ISP into the PSM system. This should include consideration of ISP at all stages in the process life cycle, particularly at three key stages: product and process development, conceptual facility planning and early design, and during routine operation (including modifications and incident investigation)
From page 69...
... OPTIONS FOR INCORPORATING ISP IN PSM There are two common approaches to formal consideration of ISP: inde pendent, stand-alone ISP reviews and incorporation of ISP into existing process safety review activities. Independent ISP Reviews An independent ISP review is conducted by a team that uses knowledge of chemistry, engineering, operation, process safety, and other relevant expertise to examine a process with the objective of understanding its hazards and finding ways to eliminate or reduce those hazards.
From page 70...
... These two approaches complement each other, and strong PSM programs incorporate both pieces. MEASURING INHERENT SAFETY When incorporating ISP into the PSM system, it would obviously be helpful to have a method for evaluating the inherent safety of any given approach.
From page 71...
... . There are also well-known process safety methodologies such as checklist and what-if analyses that have been adapted for ISP consideration, primarily in terms of identifying hazards that could be addressed by the principles of inherent safety.
From page 72...
... Gupta and Edwards (2003) Graphical approach for evaluating inherent safety based on earlier developed Loughborough Prototype Index of Inherent Safety (PIIS)
From page 73...
... (2002a) "Methodology for the integrated inherent safety and waste minimization analysis during process design." Palaniappan et al.
From page 74...
... This method utilizes process flow diagrams in early design stages. The result of the assessment is a quantification of the inherent safety of the process scheme by a set of key performance indicators.
From page 75...
... to produce the estimated probability of the worst­case accident. Once a probabilistic safety model has been developed, it can be used to compare the accident probabilities associated with different plant/process designs.
From page 76...
... This is be­ cause in such cases comparison of similar system designs by subtraction of the failure probability of one system from the failure probability of the other yields the correct difference even if both of the absolute estimates are biased. For example, suppose the estimated failure probability for System 1 is PE1 (which equals PT1 ­ PB, where PT1 is the true failure probability for System 1 and PB is the bias due to omitted error causes)
From page 77...
... To avoid this problem of underestimation, PSAs need to more carefully consider human reliability, common­cause errors and, in particular, organizational safety culture. Another consequence of underestimating the failure probability of a conventional system of active, passive, and procedural controls is that such underestimates can lead to a neglect of offsite emergency response and emergency preparedness because of the belief that they are unnecessary.
From page 78...
... 2006. Incorporation of inherent safety principles in process safety management.
From page 79...
... 1993. Assessing the inherent safety of chemical process routes.
From page 80...
... 2005. Implementing inherent safety throughout process lifecycle.
From page 81...
... 1995. The INSIDE project: Integrating inherent safety in chemical process development and plant design.
From page 82...
... 2009. Key performance indicators for inherent safety: Ap Ap plication to the hydrogen supply chain.


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