Safety analysis technique

This chapter discusses overall safety analysis techniques lor evaluating production facilities, describes the concepts used to determine where safety shutdown sensors are required, and provides background and insight into the concept of a Safety and Environmental Management Program. 

Some safety analysis techniques and their typical use are presented in Figure 3 as given by CCPS (1992). It can be seen that together these hazard evaluation methods cover well the needs of the life cycle of a process plant. However this is not a complete list but also some other methods are applicable as seen in Ch. 5. 

System Safety 2000 by Joe Stephenson. This book begins with a history of and the fundamentals of system safety. Then, the author moves into system safety program planning and management, along with system safety analysis techniques. About half of the book is devoted to those techniques. A safety generalist would find it a good and not too difficult read. 

The probabilistic approach is not apprt ale to evaluate development error occurrence. These systematic [SAE ARP4754A] errors wfll always occur when the system is exposed to the same circumstances. Due to the nature of systematic errors (i.e., it is difhcult to predict the needed circumstances), exhaustive testing and traditional safety analysis techniques are not considered sufficient protection. 

Safety-Specific Analysis. This strategy focuses on exposing and correcting the design errors that could adversely affect the hardware outputs from a system-safety perspective. Applicable safety-sensitive portions of the hardware input space and output space are analytically determined. The sensitive portions of the hardware input space are stimulated, and the output space is observed not only for the safety-sensitive intended-function requirements verification, but also for anomalous behaviours. The methods of output space observation are identified in advance, by analysis that is accomplished using traditional safety analysis techniques. 

Note that many of these attributes are not solely satisfiable by reviews and inspections. Some of them lend themselves very well to being satisfied through detailed analysis. Table 9B.9 provides a summary of the snengths and weaknesses of the different S/W safety analysis techniques. 

A comparison of safety analysis techniques Analytical calculations versus Monte Carlo simulations... 

Rouvroye, J.L van den Bliek, E.G. 2002. Comparing safety analysis techniques. Reliability Engineering System Safety 75 289-294. Elsevier... 

Gorski, J. 1994. Extending Safety Analysis Techniques With Formal Semantics, in Technology and Assessment of Safety-Critical Systems, (eds.) Redmill, F.J. Anderson, T. Springer-Verlag, 147-163. 

Afternoon—System safety analysis techniques (overview of Part 4). 

Part 11 of this text details a number of the various common system safety analytical methods and techniques that are practiced in the system safety discipline. Each of these methods or techniques is usually conducted at specific points during the project or product life cycle, as indicated in Eigure 3.4. At this point, it is important to understand that a specific system or program may require the use of any or all of the system safety analysis techniques available to today s system safety professional. Each method has its own distinct purpose and function, and, as tools, each can be quite useful. 

The failure mode and effect analysis (FMEA) is one of the more familiar of the system safety analysis techniques in use. It has remarkable utility in its capacity to determine the reliability of a given system. The FMEA will specifically evaluate a system or subsystem to identify possible failures of each individual component in that system, and, of greater importance to the overall system safety effort, it attempts to forecast the effects of any such failure(s). Because of the FMEA s ability to examine systems at the component level, potential single-point failures can be more readily identified and evaluated (Stephenson 1991). Also, although the FMEA should be performed as early in the product life cycle design phase as possible (see Figure 3.4), based on the availability of accurate data, the system safety analyst can also use this tool, as necessary, throughout the life of the product or system to identify additional failure elements as the system matures. 

As with all types of system safety analysis techniques discussed in this part of the text (Part II), a complete description of the system, its intended purpose and design functions, as well as any operational flow diagrams must also be evaluated during the performance of an SCA. If the analyst is not entirely familiar with these system characteristics, the subsequent SCA will potential be inaccurate, incomplete, and flawed. 

The system safety analysis techniques known separately as sneak circuit analysis and software safety analysis have been developed in an effort to address these concerns over system safety and reliability assurance. Although various types of sneak hazards can be identified by analysis, and a variety of software hazard analysis techniques are commonly used, each method is concerned primarily with the same essential objective explained throughout this text hazard risk elimination or reduction to acceptable levels. 

In Part II, the reader was exposed to a variety of the most common tools and techniques currently used in the system safety profession. It is hoped that the numerous examples provided will assist in developing an appreciation for system safety analysis in the evaluation of risk, no matter how complex or simple the system may be. Although these various examples did not constitute complete and detailed analyses, it is presumed that enough information has been presented to ensure a basic understanding of common system safety analysis techniques and methods. 

A closer look at some of the wider safety analysis techniques indicates that they do have some relationship with exposure and value of assets. The concept of risk analysis matrices [MoD 2004] explicitly includes impact analysis and frequency of exposure, and uses these to determine the criticality of the risk on a hazard by hazard basis. It does not, nor does it claim to, consider the role of on-going system reaction and response. In comparison, die Accident Tetrahedron explicitly includes these factors. 

System safety management provides the framework wherein the findings and recommendations resulting from the application of system safety analysis techniques can be effectively reviewed and implemented. 

In the case of our exemplar, lAT, preliminary safety activities have started to identify the types of evidence that will be considered suitable to support the claims made in the safety case to an acceptable degree of confidence. The identified types of evidence include evidence that are produced by processes common in systems adhering to older standards (such as 00-55) as well as more novel safety analysis methods. Part of the novelty of lAT derives from its SoS characteristics, and therefore novel safety analysis techniques are required. 

Another fiction relating to SoS safety cases is that the adoption of Def Stan 00-56 Issue 4 will make it difficult to construct a safety case because the onus is on the designers to argue that the right evidence has been produced in support of the safety case. However, the fact is that Def Stan 00-56 Issue 4, being a goal-based rather than a prescriptive standard, allows potentially greater flexibility in the types of evidence that can be presented in order to support the safety case and demonstrate that the system of systems is acceptably safe. Therefore the outputs of novel safety analysis techniques can be used as evidence to support the SoS safety case. 

All of the safety analysis techniques that have been discussed in this paper will support the SoS safety case by providing evidence that we have identified all LAT hazards, both hazards at traditional system boundaries and from system interactions, and that the streamlined safety analysis process for training scenarios provides a similar hazard assessment capability. 

D. Djamal, B. Lylia, B. Abdelkarim, Towards a better approach for mastering industrial risks from modeling accidental process to integrating safety analysis techniques supporting the identification of intelligent safety decision, International Journal of u- and e- Service, Science and Technology 8 (3) (2015). 

Fault Tree Analysis A system safety analysis technique used as an inductive method (top down) to evaluate fault or failure events. 

Zonal Analysis A relatively new system safety analysis technique concerned with evaluating the geographic arrangement of installed systems, and its interconnections, as well as the influence of external events on those systems. 

A systematic task analysis is essential for a good prediction of human error. The data for such an analysis come partly from logical analysis of what should happen and partly from observation of what does happen when people carry out the tasks. Such job safety analysis techniques are dealt with in chapter 2.4 of this book. 

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