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282   S o f t w a r e   &   S y s t e m s   R e q u i r e m e n t s   E n g i n e e r i n g :   I n   P r a c t i c e





                                            Has possible
                               Take X-Ray of  hazard        Hyperlink
                                  Patient
                                                 Possible overdose
                                                                    X-Ray Machine
                                                                   Hazard Analysis
                        Includes            Includes



                         Automatic,
                        Based on Patient  Manually
                         Information     Set Time
                                                        Has mitigation



                         Impacts           Impacts







                             Interlock to prevent
                             overdose to patient

                      FIGURE 11.4  Example use case with hazards and mitigating requirements


                         When extending any process model to support hazard analysis,
                      some  new  symbols  and  relationships  are  needed.  Some  suggested
                      extensions to the modeling tool used for analysis are described in
                      Table 11.3.

                      Importance of Hazard Analyses
                      Hazard analyses are sufficiently important that they are mandated by
                      regulatory agencies in various domains. Furthermore, for a product
                      to be accepted by the agency, the appropriate traces must be in place
                      (see the section on traceability in Chapter 7) and due diligence must
                      be performed to determine that

                          •  Processes are in place to support hazard analyses.
                          •  It can be proven that a full coverage check for needed hazard
                             analyses was done.
                          •  The analyses have been completed.
                          •  Where  necessary  (high  risk  =  f(severity,  probability  of
                             occurrence)), hazards have been mitigated.
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