Hazard Analysis Preliminary, Subsystem, and System

For many years, system safety engineers have made quite a bit of noise about the differences between preliminary, subsystem, and system hazard analyses. In reality, there is really only one hazard analysis. The primary objective of a hazard analysis is 

So if we say that the hazard analysis is the baseline document, then a preliminary hazard analysis (PHA) is the initial hazard assessment conducted on the system. It identifies safety-critical areas within the system and starts evaluating hazards and identifying safety design criteria and applicable safety requirements. 

A system hazard analysis (SHA) does the same thing as an SSHA except that it identifies hazards across subsystem boundaries and interfaces. It looks at system-level hazards. An SHA also should list hazard controls and verifications. 

System Safety Engineering and Risk Assessment A Practical Approach 

System The car in traffic (with all the other cars, traffic lights, weather, maintenance schedule, etc.) 

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