Transcript Template for presentations

CURRENT RESEARCH
AND
INDUSTRIAL APPLICATIONS
OF
INTEGRATED SRA AND QRA MODELS
Philip Smedley
ASA
SRA
QRA
HFA
http://mar.ist.utl.pt/saferelnet
Thematic Network on Safety and Reliability of Industrial Products, Systems and Structures
OBJECTIVE
To provide:
consistent, safe & cost-effective solutions
for a range of industrial systems
across different industrial sectors
throughout the system’s life-cycle.
PROGRAMME
Liaison
Liaison
Committee
Committee
Industrial
Committee
Steering
Steering
Committee
Committee
EU
Commission
Thematic Network
Management Dissemination & Exploitation (WP1)
Coordinator: IST
WP2
WP3
WP4
WP5
WP6
WP7
WP8
WP9
WP10
WP
leader
EQE
WP
leader
DAP
WP
leader
WP
leader
RCP
WP
leader
BUW
WP
leader
IST
WP
leader
PAFA
WP
leader
NTNU
WP
leader
WSA
WP2
Participants
WP3
Participants
WP4
Participants
WP5
Participants
WP6
Participants
WP7
Participants
WP8
Participants
WP9
Participants
WP10
Participants
ETHZ
PROGRAMME
WP
SCOPE
LEADER
1
Management, Dissemination & Exploitation
IST
2
Risk Assessment Methodology
EQE
3
Human & Org. Factors in Risk Assessments
DAP
4
Integration of Risk & Reliability Formulations
ETHZ
5
Reliability Based Design
RCP
6
Assessment of Existing Structures & Life Extension
BUW
7
Risk & Cost Based Inspection & Maintenance Planning
8
Standardisation and Codes
PAFA
9
Training and Education
NTNU
10
Strategy in the Various Industrial Sectors
Atkins
IST
UK PARTNERS
EQE International
PAFA Consulting Engineers
Atkins
BOMEL Limited
Petrellus Limited
CorrOcean Ltd
Liverpool John Moores University
University of Liverpool
The University of Surrey
Network Rail
Highways Agency
Health and Safety Executive
INTEGRATION
ASA
SRA
QRA
HFA
ADVANCED STRUCTURAL ANALYSIS
STRENGTHS
• Solutions to complex / time-dependent problems
• Speed – cost-effective solutions
• System’s redundancy and reserve strength
• Uncertainty analysis – parametric variations
WEAKNESSES
• Difficult to estimate accuracy in results
• Potential errors or inadequacies in programs
• Potentially inadequate user skill levels
STRUCTURAL RELIABILITY ANALYSIS
STRENGTHS
• ‘Complete’ representation of loading and
resistance uncertainties in design problems
• Fully quantified reliability estimates
• Updated estimates as new data added or
improved by expert opinion (Bayesian updating)
WEAKNESSES
• Better for empiric rather than parametric formulae
• If human factors are included they are generally
fairly crude or simplistic estimates.
QUANTIFIED RISK ASSESSMENT
STRENGTHS
• Causes and consequences of hazard modelled
• Strong for operational and accident problems
• Quantification of underlying issues - based on
incident data and expert opinion (frequentist)
WEAKNESSES
• Lack of data or understanding of problem or
inaccurate data due to biased opinions
• Uncertainty only considered in the underlying
statistics rather than the model
• Not good for time-dependent problems
HUMAN FACTOR ASSESSMENT
STRENGTHS
• Most (80%) incidents caused by human error
therefore essential element in our understanding
• Human behaviour often very predictable
• Includes individual and corporate behaviour
WEAKNESSES
• Cynicism - knowledge of HFs generally from
specialists outside the engineering industry
• High uncertainties in models and data (for now)
• Difficult issues of cultural/society differences
SRA-QRA-HFA INTEGRATION
IS IT FEASIBLE?
A Qualified - Yes.
A number of common issues:
• Mathematical models are of a similar format
• All seek to achieve a target level of safety
(Annual target reliability or risk acceptance criteria)
• Need quality, unbiased data (historic or opinion)
SRA-QRA-HFA INTEGRATION
INITIAL INTEGRATED MODELS
1. Reliability distribution replaces deterministic
quantification in risk analysis - fault tree
2. Human factor Bayesian Probabilistic Networks
can readily be reformulated into fault trees
INTEGRATION – Example 1
INST. FOR ELECTRIC POWER RES. (HUNGARY)
1. Process Analysis – Deterministic Assessment
1. Initiating event identification
2. Event tree development
2. System Analysis – Reliability Assessment
1. Fault tree development
2. Hardware failure data estimation
3. Human failure data estimation
3. Structural Analysis – Fragility Assessment
INTEGRATION – Example 1
INTEGRATION – Example 2
SWALE CROSSING : Kent – Isle of Sheppey
INTEGRATION – Example 2
PAFA CONSULTING ENGINEERS
1. Risk Analysis – AASHOTO Guidelines
1. Number of Ships subdivided into 6 classes
2. Probability of aberrance (human error, mechanical
failure, severe environmental loading)
3. Probability of collision with bridge pier
4. Probability of exceeding bridge pier strength
2. To Probability of Aberrance add:
1. Mechanical reliability of bridge lift mechanism
2. Avoidance of other vessels in area (esp. yachts)
PROBLEM: ACCEPTANCE CRITERIA
from Faber/Schneider
Objective Hazard Potential
Correct model
Accepted
Risk
Accurate Risk
Assessment
Not
adequate
Adequately quantified (good data)
Wrong
Accepted Risk
Risks modelled
Neglected
Taken into account
Not Realised
Subjectively realised
Inaccuracies due
to Human Errors
Not known
Objectively known
SRA-QRA-HFA INTEGRATION
IS IT DESIRABLE?
Sometimes
• Expanding a reliability model, for example, to
account for poorly defined human factors will
add time and cost but not improve the overall
understanding of the system.
• The three approaches have been developed to
solve specific problems. Each approach has
many models each with specific strengths and
weaknesses. One integrated approach is likely
to be less rigorous in some instances.
SRA-QRA-HFA INTEGRATION
SAFERELNET APPROACH
• Seeking to develop a consistent mathematical
model that may be used to integrate some of the
strengths of SRA – QRA – HRA.
• If such an integrated approach can be
developed, to consider the strengths and
weaknesses within such a model.
• Discuss and develop thinking for a consistent
risk and reliability acceptance criteria.
http://mar.ist.utl.pt/saferelnet