System hazard analysis , preliminary

Again the process involves a preliminary hazard analysis to be done very early in the concept stage, followed by subsystem hazard analysis as subsystems are developed, systems hazard analysis that looks at interfaces between subsystems, and, finally, the operating hazard analysis, which tends to add the human element and evaluate procedures. 

Laundry lists of analyses frequently mix types of analyses (preliminary hazard analysis, system hazard analysis, and operating hazard analysis) with the methods or techniques for performing analyses (fault tree analysis, energy trace and barrier analysis, failure modes and effects analysis, common cause analysis, change analysis, and so on). Whether fault hazard analysis is a type or a method depends upon the reference in use. For all practical purposes, fault hazard analysis and system (or subsystem) hazard analysis seem to be the same thing, which is apparently called gross hazard analysis occasionally. 

Hazard identification is continued throughout the design stage and documented in the preliminary hazard analysis (PHA), subsystem hazard analysis (SSHA), and the system hazard analysis (SHA). Even though the primary purpose of these products is to analyze previously identified hazards and to determine the adequacy of controls, every effort should be made to continue to identify new hazards, especially those associated with interfaces and changes. 

After the PHA is complete, first subsystem hazard analysis (SSHA) and, if required, system hazard analysis (SHA) are performed. Depending on the nature and complexity of the end product and the results of the PHA, SSHAs may be performed on all subsystems or just on selected critical subsystems. Unlike MIL-STD-882B, software analyses are not generally identified separately. If applicable, preliminary software hazard analysis is part of the PHA. Software should be treated as a subsystem and, if further software analysis is required, an SSHA can be performed on the software. 

The purpose of the project evaluation tree is to provide a relatively simple, straightforward, and efficient method of performing an in-depth evaluation or analysis of a project or operation. It is best suited for performing operating hazard analysis and accident analysis. It can also be a valuable review and inspection tool. If adequate information is available, PET analysis may be helpful in performing preliminary hazard analysis, subsystem hazard analysis, and system hazard analysis. 

Fault hazard analysis is mentioned very frequently in system safety literature, sometimes as a type of analysis and occasionally as a technique. One NASA system safety document (NHB 1700.1-V3, System Safety) describes it as the analysis to be performed after the preliminary hazard analysis for further analysis of systems and subsystems and suggests that it can be either a separate analysis or an extension of the failure modes and effects analysis (NASA 1970). Most programs today (including NASA) refer to this analysis as the subsystem hazard analysis (SSHA) and the system hazard analysis (SHA). 

During the concept phase, historical data and technical forecasts are developed as a base for a system hazard analysis. A Preliminary Hazard Analysis (PHA) is conducted during this phase. At the gross level, a Risk Analysis (RA) is performed to ascertain the need for hazard control and to develop system-safety criteria. Safety management will be doing the initial work on the System Safety Program Plan (SSPP). Three basic questions must be answered by the time the concept phase is completed ... 

The ETBA is an analytical technique which can be of great assistance in the preparation of the preliminary hazard list (PHL). It can also be quite useful in the development of a Preliminary Hazard Analysis (PHA), Subsystem Hazard Analysis (SSHA), or the more general System Hazard Analysis (SHA). The ETBA can also be used, depending on the specific system under consideration, in the development of the Operating and Support Hazard Analysis (O SHA), and, of course, during the MORT process from which the ETBA evolved. 

Systems Hazard Analysis (SHA) is a qualitative method combining aspects of preliminary hazard analysis and failure-mode and effect analysis (Firenze 1973). Its emphasis is on work-tasks performed in various operational procedures. SHA adds two important pieces of information to those methods previously discussed the standards or regulations violated and the relevant subsystem. It chooses a task activity or a dynamic event as the focal point of the analysis rather than a more static component. As with the other methods, an analyst with detailed knowledge of the system is required. 

As we shall see in Chapter 5, the PHA is used in support of the Preliminary Design Review (PDR) milestone to develop the requirements for new procurements while developing the statement of work or procurement specification for new hardware for the program. Completion of the PHA is required in support of the PDR to verify that the technical safety requirements have been incorporated into the preliminary design of the item for procurement. Hazards identified in the PHA will be updated in the System Hazard Analysis (SHA) and the Subsystem Hazard Analysis (SSHA) as the life cycle progresses. 

Partial what-if analyses for the two example processes described in Section 4.0 are shown in Tables 4.9 and 4.10. Although for actual, more complex analyses, the what-if tables for each line or vessel would be separate, for these examples, a single table was developed. A preliminary hazard analysis (PHA) would identify that the intrinsic hazards associated with HF are its reactivity (including reactivity with water, by solution), corrosivity (including carbon steel, if wet), toxicity via inhalation and skin contact, and environmental toxicity. The N2 supply system pressure is not considered in this example. The specific effects of loss of containment could be explicitly stated in the "loss of HF containment" scenarios identified. Similarly, the effects of loss of chlorine containment, including the reactivity and toxicity of chlorine, could be specified for the second example. 

Assessment. An analysis of the hazards present in this laboratory show the most significant hazard to be the release of vapor CSM from engineering controls and into the workplace. The significance of this hazard mandates further efforts in system safety in the form of a Preliminary Hazard List (PHL) and a Preliminary Hazard Analysis (PHA). The user must in this instance take an active role in the design review process. 

Other possible preliminary safety analysis methods are concept safety review (CSR), critical examination of system safety (CE), concept hazard analysis (CHA), preliminary consequence analysis (PCA) and preliminary hazard analysis (PHA) (Wells et al., 1993). These methods are meant to be carried out from the time of the concept safety review until such time as reasonably firm process flow diagrams or early P I diagrams are available. 

PA PCP PCR PFA PGB PHA PID PLC PMACWA PMD POTW ppm PRH PRR psi psig PTFE PVDF PWS picric acid pentachlorophenol propellant collection reactor perfluoroalkoxy product gas burner preliminary hazards analysis proportional integral differential controller programmable logic control Program Manager for Assembled Chemical Weapons Assessment projectile mortar demilitarization (machine) publicly owned treatment works parts per million projectile rotary hydrolyzer propellant removal room pounds per square inch pounds per square inch gauge polytetrafluoroethylene (Teflon) polyvinylidene fluoride projectile washout system... 

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