Passenger-Carrying Submersible Example

An example PHL is shown in Table 5.1. The Coast Guard followed the same process described earlier (Hathaway, 1989). Notice that the hazard list varies somewhat from the hazard category list. The reason is that each system is unique, and therefore, hazards and their categories could be different. Also, the list really is a compilation of hazard sources. Each item is actually a compact description of many more individual hazards, which are too numerous to show here. 

The functional tree is obviously a hierarchical structure, going from the more general top item—or total system name—to the more specific subelements (i.e., Ufe support systems). You walk through each item in the functional tree and develop a PHL. 

FIGURE 5.3 Passenger-carrying submersible functional tree. (From Hathaway, W.T. and Markos, S.H., Passenger Carrying Submersibles System Safety Analysis, DOT-TSC-CG-89-2, U.S. Department of Transportation, Washington, DC, 1989.) 

As you go through a system, it very rapidly becomes apparent that hazards are not always well confined within one subsystem but actually reach aCTOss various barriers, both physical and functional. 

A lot of people who are doing hazard analysis for the first time ask me how do I take all these disparate data and make sense of them. This looks a little crazy bnt is something that I ve picked up over the years doing lots and lots of hazard analyses. I call my approach the 3D approach. Here it is  

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Continuing our passenger-carrying submersible example, the safety assessment would look something like the one shown in Table 5.6. 

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