1 SKJ©DNV Cost Effectiveness of Hull Girder Safety Rolf Skjong & EM Bitner-Gregersen Det Norske Veritas OMAE, Oslo, June 24-28, 2002

2 SKJ©DNV Content  Acceptance criteria in Structural Reliability Analysis  Acceptance Criteria in Formal Safety Assessment  Common Criteria?  Application to Hull Girder Strength  Conclusion

3 SKJ©DNV Traditional Approach - SRA  Typical Example:DNV Classification Note 30.6 (1992) on Structural Reliability Analysis of Maritime Structures  SRA is Bayesian theory  Explains why SRA does not produce Probabilities with a frequency interpretation –No gross error –Epistemic uncertainty & model uncertainties included –SRA talk of “notional” reliabilities

4 SKJ©DNV Traditional Approach - SRA  Target should depend on consequence  Calibration against known cases (that are acceptable good/best practices in the industry)  Calibration against similar cases with similar consequences  Based on accepted decision analysis techniques  Based on tabular values (presented as a last resort)

5 SKJ©DNV Traditional Approach - SRA  Based on tabular values (presented as a last resort)

6 SKJ©DNV Traditional Approach - RA  Quantitative risk assessment is the basis for regulations in many industries –PSA/PRA - Nuclear –Hazardous Industries (Seveso I/II) –Offshore (Safety Case) –Shipping (FSA) –Etc.

7 SKJ©DNV Risk Assessment  Two uses of Risk assessment  Use as a basis for receiving and maintaining a licence to operate (the plant, platform etc.) –Safety Case  Use as a basis for implementing risk reducing measures for “populations (all cars, all ships, all planes etc.) –Formal Safety Assessment

8 SKJ©DNV Traditional Approach - QRA  Present Risk Results in terms of –Individual Risk (Fatalities) –Individual Risk (Health and Injuries) –Societal Risk (Group Risk) –Environmental Risk –Economic risk (not necessarily a regulatory issue)

9 SKJ©DNV Traditional Approach - RA  Example Individual risk

10 SKJ©DNV Traditional Approach - QRA  Example Societal Risk

11 SKJ©DNV Traditional Approach - QRA Low Risk High Risk Intolerable ALARP Negligible Not acceptable Acceptable Acceptable if made ALARP

12 SKJ©DNV Traditional Approach - QRA  The As Low As Reasonably Practicable Area implies that cost effectiveness assessment may be used  Risk is made As Low As Reasonably Practicable, when all cost effective safety measures have been implemented  Implies that a decision criteria for cost effectiveness will be required  It seems to be accepted at IMO that most ship types are in the ALARP area but not ALARP  Cost Effectiveness will be the only criteria

13 SKJ©DNV Common Criteria  Cost effectiveness criteria is easy to use, both for SRA and FSA studies  Advantage to SRA: Only change in risk is used in the decision process, not the absolute numbers  Criteria to use: $ $ 3.0 million  Decision at MSC 76 in December 2002

14 SKJ©DNV Previous IMO decisions  Example from IMO: UN Organisation for maritime safety and environmental protection regulations

15 SKJ©DNV Previous decision By reallocation lives could be saved annually in the US $ = $ 1.5 million

16 SKJ©DNV Girder Collapse/Sagging

17 SKJ©DNV PROCODE  Use limit states formulation with target beta –Optimisation of partial safety factors –Control Variables: Partial Safety Factors –Minimum Scatter around a target reliability by minimising the penalty function –Target to vary to produce cost effectiveness ratios

18 SKJ©DNV PROCODE Subjected to : With one of the inequalities turning into equality One design Case : This is generalised to Multiple design cases in PROCODE

19 SKJ©DNV PROCODE  Programmable functions –Limit States –Code Checks –Penalty functions  Defined by Data (additional to PROBAN) –Scope –Safety Factor –Design Parameter

20 SKJ©DNV PROCODE RESULTS  Code Evaluation (before optimisation starts)  Optimised partial safety factors  Resulting reliabilities  Resulting design parameters (input to cost analysis)

21 SKJ©DNV PROCODE Results

22 SKJ©DNV PROCODE Results

23 SKJ©DNV Resulting Steel Weight

24 SKJ©DNV Costs

25 SKJ©DNV Costs

26 SKJ©DNV GCAF Calculation of GCAF (L Profiles) GCAF = (Cost of RCO)/(  PLL)  -> 3.50 to 3.72 (P f = to )  P 20 persons20 years  PLL = ( ) = % survives GCAF = (4,309,760 -3,997,769)/ = $ 10.3 million

27 SKJ©DNV NCAF Calculation of NCAF (L Profiles) NCAF = (Cost of RCO -Economic Benefits)/(  PLL)  -> 3.50 to 3.72 (P f = to )  P 20 years Benefits = ( ) 20 ($11 + $ 21 million ) = $ 90,240 Old Ship NCAF = (4,309,760 -3,997,769-90,240)/ = $ 7.13 million Cargo

28 SKJ©DNV Results

29 SKJ©DNV Conclusion  In reliability based code calibration CEA (NCAF) may be used as an alternative to target   Consistency with RA  The decision is based on the derivative of P F with respect to design variables only  Not reliant on probability (the absolute number)  Mid ship bending moment (ship deck/sagging) –NCAF at about $ 3 million corresponds to target –Compares well to last line of defence, lifeboats at $ 1 million  More studies necessary for other limit states

30 SKJ©DNV One criteria HE, QRA, SRA Human error, navigation Collision Flooding Evacuation Failure Fire Optimising risk control options according to their cost effectiveness: