System safety analyzing

LOPA is a semi-quantitative tool for analyzing and assessing risk. This method includes simplified methods to characterize the consequences and estimate the frequencies. Various layers of protection are added to a process, for example, to lower the frequency of the undesired consequences. The protection layers may include inherently safer concepts the basic process control system safety instrumented functions passive devices, such as dikes or blast walls active devices, such as relief valves and human intervention. This concept of layers of protection is illustrated in Figure 11-16. The combined effects of the protection layers and the consequences are then compared against some risk tolerance criteria. 

The list of selected failure modes is an input to the failure mode injection campaign. The objective of this step is to analyze the consequences of each particular failure mode on the system safety properties. Each failure mode is modeled by altering the CSP specification of the system. 

If the verification confirms that the analyzed failure mode has no negative effects on system safety, the failure mode can be accepted. In the opposite case however we know that the failure mode, if actually occurs, can affect the system safety properties. In such case FDR can provide example event scenarios that lead to a contradiction of safety. Those scenarios can then be very helpful while considering possible redesign of the component objects. The results of the failure mode injection campaign are collected in the OF-FMEA tables (see Table 1). 

ABSTRACT Determination of resistance of mine ventilation system is an important part of safety production of coal mine and ventilation safety management, the size of the resistance directly influence the effect of the mine ventilation. In order to understand the No. 4 Mine of Pingdingshan Coal Field mine ventilation resistance and its distribution, the optimization of mine ventilation system, selected major determinations, based on the basis of the barometer method for determination of resistance to the mine, and according to the results of mine ventilation system are analyzed. 

Social system safety control structures often are not designed but evolve over time. They can, however, be analyzed for inherent risk and redesigned or reengineered to prevent accidents or to eliminate or control past causes of losses as determined in an accident analysis. 

In analyzing an existing organizational or social safety control structure, one of the first steps is to determine where the responsibility for implementing each requirement rests and to perform a gap analysis to identify holes in the current design, that is, requirements that are not being implemented (enforced) anywhere. Then the safety control structure needs to be evaluated to determine whether it is potentially effective in enforcing the system safety requirements and constraints. 

Simply put, system safety is the name given to the effort to make things as safe as is practical by systematically using engineering and management tools to identify, analyze, and control hazards [p. 12]. 

The system safety concept involves a planned, disciplined, systematically organized and before-the-fact process characterized as the identify-analyze-control method of safety [p. 9]. 

Applying system safety as an orderly examination of an established system or subsystem to identify, analyze, avoid, elintinate, or control hazards can be successful in the less complex situations, without using elaborate analytical methods. 

The HERMES methodology was first introduced by Cacciabue (2004a,b) for analyzing the HMI in complex contexts. HERMES is strucmred in a number of steps to preserve the basic requirements of congruence and consistency between both types of retrospective and prospective studies as well as to underpin the correspondence between recurrent HMI analysis and system safety and integrity. 

In 1985, the American Institute of Chemical Engineers (AIChE) initiated a project to produce the Guidelines for Hazard Evaluation Procedures. This document, prepared by Battelle, includes many system safety analysis tools. Even though frequently identified as hazard and operability (HazOp) programs, the methods being developed by the petrochemical industry to use preliminary hazard analyses, fault trees, failure modes, effects, and criticality analyses, as well as similar techniques to identify, analyze, and control risks systematically, look very much like system safety efforts tailored for the petrochemical industry (Goldwaite 1985). 

The primary objectives of the system safety effort are to identify, analyze, and control hazards to the extent possible with constraints of operational effectiveness, time, and money. 

System safety may grow as a separate discipline or the system safety effort may be absorbed into the mainstream of industrial safety, loss prevention, risk management, loss control, or some other program. A new name or buzzword may appear. Nevertheless, the need for first-time safe systems and for the application of system safety principles, tools, and techniques to systematically identify, analyze, and control hazards as early in the life cycle as possible (with continuing efforts throughout the life cycle) will continue to grow indefinitely. 

A system safety effort would also be appropriate for a hospital, hotel, restaurant, travel agency, or department store. A systematic, upstream effort to identify, analyze, and control hazards is an appropriate way to improve workplace safety even in service organizations. Again, two programs may be appropriate, one that focuses internally on the safety of employees and staff and a second that focuses on the clientele. 

Most of the system safety effort involves providing a service. That service is to identify, analyze, and control hazards as early in the life cycle as possible in order to produce cost-effectively a safer end product. Several products are produced as part of the system safety effort. These products (all documents) communicate and document risk information to management and provide a means of monitoring and auditing the effort. 

The accident analysis report determines and documents the root causes of accidents associated with the end product and includes new hazards, hazards inadequately controlled or analyzed, and new baseline information identified by the accident analysis in the system safety effort. 

Similarly, major changes or modifications to the end product should be formally analyzed as part of the system safety effort. Recommendations and corrective action resulting from accident or change analyses should not be documented, reviewed, or tracked differently than corrective actions from other system safety analyses. 

The design engineer, aided by the system safety working group, systematically reviews all aspects of systems to determine why and how persons may use the system, subsystem, or component improperly and attempts to identify, analyze, and control hazards associated with misuse. 

In the strictest sense, system safety encompasses process safety and the two are inextricably linked. Since systems are defined to include processes, process safety may be considered a subset of system safety. The application of appropriate system safety tenets to the chemical process industry follows. In the process industry, the system safety practitioner continues his or her quest to identify, evaluate, analyze, and eliminate or control hazards throughout the life cycle of the process (in this case). The precedence of controls remains the same. So, there is a close relation between system and chemical process safety and the process industry. 

A qualitative investigative safety review technique. It was developed in the 1950s by reliability engineers to determine problems that could arise from malfunctions of military systems. Failure mode and effects analysis is a procedure by which each potential failure mode in a system is analyzed to determine its effect on the system and to classify it according to its severity (Figiue F.l). When the FMEA is extended... 

The respective locations of the sample system and analyzer The sample system should be well suited to the intended analysis. The representative sample must be taken where it will give the most insight of the process, and sample transportation must be timely so that the analysis can be used for real-time process control. Sample return should be considered as well if the sample would create any environmental, health, or safety problems. The analyzer must be well... 

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. 

The JSA, then, is a specialized approach of task analysis that takes an existing job and analyzes its tasks to specifically identify hazards encountered in the work environment. At the very least, the JSA does have a place within the system safety process as a tool to evaluate the hazards or risks of an existing task or function during the operation phase of the project life cycle. Here we see another connection between the principal elements of the industrial safety process and one of the basic objectives of the system safety effort, namely, that the JSA tries to eliminate or control the risk of hazard exposure in a given task during the life of the project. 

In order to utilize the ETBA in the performance of the system safety analyses listed above, certain essential data are required for evaluation. For example, if the ETBA is to be performed on a specific manufacturing facility, then the analysis should begin with an examination of completed facility drawings. If the ETBA is concerned with a specific project, or a newly designed piece of manufacturing equipment, the project plans and schematics must be evaluated. It should be noted that the level of detail required is dependent on the analysis itself. Development of a preliminary hazard list will not require extensive detail and evaluation, whereas an ETBA in support of a subsystem hazard analysis will meticulously analyze the project to the component level and detailed drawings will, therefore, be required. 

Software hazard analysis (SWHA) is a system safety analytical technique whose primary function is to systematically evaluate any potential faults in operating system and applications software requirements, codes, and programs as they may affect overall system operation. The purpose of the SWHA is to ensure that safety specifications and related operational requirements are accurately and consistently translated into computer software programs. In this regard, the analysis will verify that specific operational safety criteria, such as failsafe or fail-passive, have been properly assimilated into operational software. The SWHA will also identify and analyze those computer software programs, routines, or functions that may have direct control over or indirect influence on the safe operation of a given system. Also, in the operation of the computer software command function, there is a potential that the actual coded software may cause identified hazardous conditions to occur or inhibit a desired function, thereby creating additional hazard potential. 

The OSHA Process Safety Standard incorporates many system safety concepts. Also see Chapter 24. For example, the standard calls for an experienced team to identify and analyze hazards (process hazard analysis or PHA) using one or more of the following methods ... 

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