Probabilistic Risk Assessment and Conceptual Design

1
Probabilistic Risk Assessment and Conceptual
Design

• Bryan C Fuqua SAIC
• bryan.c.fuqua_at_nasa.gov
• 281.335.2282
• Diana DeMott SAIC
• diana.l.demott_at_nasa.gov
• 281.335.2056
• Paul Wilson SAIC
• paul.wilson-1_at_nasa.gov
• 281.335.2291

2
What is PRA?

• Determining risk generally amounts to answering
  the following three questions
• What kinds of events or scenarios can occur
  (i.e., what can go wrong)?
• What are the likelihoods and associated
  uncertainties of the events or scenarios?
• What consequences could result from these events
  or scenarios (e.g., Loss of Crew and Loss of
  Mission)?
• Probabilistic Risk Assessment (PRA) is a
  comprehensive, structured, and logical analysis
  method aimed at identifying and assessing risks
  in complex technological systems for the purpose
  of cost-effectively improving their safety and
  performance. (PRA Procedures Guide for NASA
  Managers and Practitioners)
• They are often characterized by (but not limited
  to) event tree models, fault tree models, and
  physics based simulation models

3
Why Use PRA for Planning or Early in Concept
Phase?

• PRA can be applied in the conceptual design phase
  and not just the operational phase
• PRA can be utilized as a
• key input to the Risk Informed
• Decision Making process
• Identifies potential risks early to
• Determine what (equipment, process, mission,
  etc.) drives the risk
• Mitigate or eliminate risks earlier in design to
  lower costs
• Allows trade studies to compare design
  alternatives based on risk

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Use of PRA in Trade Studies

• Provide additional information for Risk Informed
  Decisions made by management
• Compare concept/design alternatives based on
  risks
• Determine magnitude of reduced risk due to
  proposed changes in
• Design
• Process
• Equipment / components

5
Using PRA Methodology

• Develop high level PRA models of Design Reference
  Missions (DRMs) or early design prototypes
• Models may include Event Trees, Fault Trees, or
  other probabilistic-based applications
• Models should be based on conceptual designs and
  generic key system and equipment level
  information
• Using what is known today, we can quantify the
  model(s) to predict magnitudes of risk, or
  compare risks, for different designs
• Following this methodology will provide
  program/project management with a better
  understanding of the risks

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Key PRA Parameters to Develop

• Establish the scope of the model
• Understand and incorporate success criteria
• Use a high level approach to provide magnitude of
  (not specific) risk
• Master Equipment List (MEL)
• Find data (e.g., historical data, surrogate data,
  etc.)
• Use placeholder data for known future
  considerations

7
PRA Results (Risk Drivers)

• Identify and characterize the key risks and
  challenges associated with potential high risk
  programs in aerospace or other industries
• Loss of life
• Loss of equipment or facility
• Large financial loss

8
Conclusion

• PRA methodology is a tool that has the potential
  to improve both conceptual planning and early
  design efforts to help identify and ultimately
  mitigate risks in a more efficient and cost
  effective manner.