Process safety analysis definitions

The Center for Chemical Process Safety s projects fall into a number of general topic areas that comprise a comprehensive program. These topic areas include identification of hazards and analysis of risks, prevention and mitigation of the hazards identified, and better definition of areas affected by a release of hazardous materials. This book is the latest in the series dealing with hazard identification and risk analysis. 

The job safety analysis (JSA) [also referred to as the job hazard analysis (JHA)], which is a more simplified form of task analysis, has been a longstanding tool for task and function analysis. JSA has been available and utilized in general industry for many years by the industrial safety community. However, many practitioners do not understand or are simply unfamiliar with the connection between the JSA and the system safety tasks of hazard identification and analysis. It has even been suggested by some in the profession that the JSA itself is a type of oversimplified system safety analysis and, if performed earlier in the job development phase, could be used as the basis of a preliminary hazard analysis for a specific task or set of tasks. However, because JSA is often (if improperly) used to analyze a function only after it has been implemented, much of the data is not factored into the system safety process. The primary purpose of the JSA is to uncover inherent or potential hazards that may be encountered in the work environment. This basic definition is not unlike that previously discussed regarding the various system safety analyses. The primary difference between the two is subtle but important and is found in the end-use purpose of the JSA. Once the job or task is completed, the JSA is usually used as an effective tool for training and orienting the new employee into the work environment. The JSA presents a verbal picture of a specific job. 

A Center for Chemical Process Safety (CCPS) publication gives the following definition An IPL is a device, system or action which is capable of preventing a scenario from proceeding to its undesired consequence independent of the initiating event or the action of any other layer of protection associated with the scenario. The effectiveness and independence of an IPL must be auditable [12]. Discussions on layer of protection analysis (LOPA) were covered in Chapter V, so they are not repeated here. However, a few characteristic features of protection layers are presented. Similar to fault tolerance and security, this is also important so that the control system is always safe. As per lEC 61511 standard the core idea for integrated safety and security is defense-in-depth with independent layers of protection to reduce process risk. The strategy behind this is that the BPCS, critical... 

Our model has three main parts. The first part consists of the EC 61508 steps needed for developing the environment description and then the phases 1-4 (concept, overall scope definitions, hazard and risk analysis and overall safety requirements). These initial steps result in the initial requirements of the system that is to be developed. This is the key input to the second part of the model, which is the Scrum process. The requirements are documented as product backlog items. A product backlog is a list of all functional and safety related system requirements, prioritized by the customer. We have observed that the safety requirements are quite stable (e.g. the response time has to be less than the Process safety time for a fire alarm system), while the functional requirements may change considerably over time. Development with a high probability of changes to requirements will favour an agile approach. 

The Initial Change Safety Analysis (ICSA) is done at two levels. Firstly, when the system definition is estabhshed, each of the boundary interfaces identified within the process models should be subjected to ICSA as already discussed earlier. This is essentially a stmctured review process, wherein interfaces ate systematically reviewed by a group of experts against predefined criteria as explained earlier. 

There are many definitions of safety, and sometimes a distinction is made between systems being safety critical and safety related, dependent on the degree of harm they can cause. We take the view that safety is concerned with absolute harm, that is irremediable or irrecoverable damage. The damage can be to individuals, to property, or to the environment. Safety is a systems issue. Computer systems, and hence software, can only influence safety if they are used to control some physical process which can lead to harm. Thus, although we wish to build computer based tools to support safety analysis, our aim is to support safety cases about systems implemented in a mixture of technologies, and involving humans, not simply implemented as computer systems or in software. 

On the basis of the results of these analyses, the requirements for the safety system are elicited. Specialists in nuclear safety and other engineering disciplines, as appropriate, should contribute to the definition of the requirements for the safety system. Normally, changes to the initial design are necessary and a new design is created, followed again by safety analysis. After a few iterations, a configuration of mechanical, process and I C systems is reached in which all current nuclear safety requirements are met. 

Rinard dedicated his research to a detailed analysis of methodological aspects of a micro-reactor plant concept which he also termed mini-plant production [85] (see also [4, 9, 10] for a commented, short description). Important criteria in this concept are JIT (Just-in-time) production, zero holdup, inherent safety, modularity and the KISS (keep it simple, stupid) principle. Based on this conceptual definition, Rinard describes different phases in plant development. Essential for his entire work is the pragmatic way of finding process solutions, truly of hybrid character ]149] (miniaturization only where really needed). Recent investigations are concerned with the scalability of hybrid micro-reactor plants and the limits thereof ]149], Expliddy he recommends jointly using micro- and meso-scale components. 

The only way to avoid this is by strict analysis of the supply chain from the customer order to final product delivery. Definition of the optimized (theoretical) process and sequential work towards a high service level approach allow the identification of gaps, and of opportunities which might not always be the cheapest (ship versus train versus plane) but could be the most effective way to reduce capital costs and shorten planning scope - an important aspect, especially in volatile customer markets with long production processes on the (chemical) supplier side. As in the case of CIP, this needs clear parameters, KPIs, commitment from all players, and regular tracking. The most important parameters are the lead time for all products, optimal lot sizes, replenishment points, and safety inventories. 

This chapter presents the basic concepts and definition of risk (Section 3.1), a protocol for conducting transportation risk assessments (Section 3.2), and a prioritization process for identifying important issues and transportation scenarios requiring a more detailed risk analysis (Section 3.3). Due to the differences in safety and security definitions and risk assessment methodologies, the focus of Chapters 3, 4, and 5 is limited to transportation safety. Security concepts, definition, and assessment methods are presented separately in Chapter 6, with this chapter providing a high-level comparison of safety and security. 

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