Subsystem hazard analysis risk assessment

The subsystem hazard analysis report contains a description of the subsystem and a narrative summary of key findings that specifically address the adequacy of the controls placed on any high hazards associated with the end products, the level of residual risks that remain after controls have been applied, and recommendations for further analysis or testing. The report should also describe the techniques and methodology used in performing the analysis, including risk assessment and risk acceptance criteria. The report should also contain the hazard report worksheets used in the study. 

System safety should be involved in the PDR, typically making a presentation summarizing the safety effort to date, the DSFs in the system design, and the current level of mishap risk which the design presents. System safety provides, as a minimum, a subsystem hazard analysis (SSHA), SHA, safety assessment report (SAR), and final safety requirements for this review. 

As a project is developed and more detailed design data are available, a system hazard analysis (SHA) and subsystem hazard analyses (SSHAs) may be conducted to provide more detailed, in-depth risk assessment information. Two of the more widely used techniques for performing SHAs and SSHAs are the failure modes and effects analysis (FMEA) and fault tree analysis (FTA). 

Faults are analyzed through a graphical representation of causality known as Fault Tree Analysis (FTA). Faults are used to analyze the effect of failures on the system, subsystem, or operating environment (i.e., to facilities, equipment, or personnel). Failures are associated with a quantitative analysis of the design of the system. Hazards are assessed qualitatively, aud must be analyzed and either eliminated or reduced to an acceptable level of risk through a mitigation process. The relationship between faults, failures, and hazards may best be understood as follows not aU faults are failures and not aU failures present a hazard to the system. 

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