Software Preliminary Hazard Analysis

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 recommended techniques for preliminary hazard analysis are energy trace and barrier analysis (ETBA) and failure modes and effects analysis (FMEA). Recommended techniques for system and subsystem hazard analyses are FMEA, fault tree analysis (FTA), common cause analysis, sneak circuit analysis (for electrical, electronic, and some hydraulic or pneumatic circuits) and, of course, software hazard analysis for software. 

Software Preliminary Hazard Analysis This type of analysis is used to identify software program routines that are considered to be safety-critical, and thus is conducted prior to software program coding. To perform the analysis, the analyst should make reference to any available system specifications, interface documentation, functional flow diagrams, software flowcharts, storage and file allocation specifications, and any other program descriptive information. 

Concept stage In the Concept stage, the requiranents of the stakeholders are identified, clarified, and documented. Subsystem elements of the overall system are generated. Hardware and software modeling are used in order to establish the requirements, and begin to validate the systan design. Safety objectives are documented and the Preliminary Hazard Analysis (PHA) is performed. 

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