CURRENT RESEARCHAND

INDUSTRIAL APPLICATIONSOF

INTEGRATED SRA AND QRA MODELS

Philip Smedley

ASA SRA QRA

HFA

Thematic Network on Safety and Reliability of Industrial Products, Systems and Structures

http://mar.ist.utl.pt/saferelnet

OBJECTIVETo provide:

consistent, safe & cost-effective solutions

for a range of industrial systems

across different industrial sectors

throughout the system’s life-cycle.

Steering

Committee

Thematic Network Management Dissemination & Exploitation (WP1)

Coordinator: IST

EU Commission

WP5 WP leader RCP

WP4 WP leader ETHZ

WP6 WP leader BUW

WP7 WP leader IST

WP8 WP leader PAFA

WP3 WP leader DAP

WP9 WP leader NTNU

WP2 WP leader EQE

WP10 WP leader WSA

WP2 Participants

WP3 Participants

WP4 Participants

WP5 Participants

WP6 Participants

WP7 Participants

WP8 Participants

WP9 Participants

WP10 Participants

Industrial Committee

Liaison Committee

SteeringCommittee

LiaisonCommittee

PROGRAMME

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 IST

8 Standardisation and Codes PAFA

9 Training and Education NTNU

10 Strategy in the Various Industrial Sectors Atkins

EQE InternationalPAFA Consulting Engineers

Atkins BOMEL Limited

Petrellus LimitedCorrOcean Ltd

Liverpool John Moores UniversityUniversity of Liverpool

The University of SurreyNetwork Rail

Highways AgencyHealth and Safety Executive

UK PARTNERS

ASA SRA QRA

HFA

INTEGRATION

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 Assessment1. Initiating event identification

2. Event tree development

2. System Analysis – Reliability Assessment1. Fault tree development

2. Hardware failure data estimation

3. Human failure data estimation

3. Structural Analysis – Fragility Assessment

INTEGRATION – Example 1

SWALE CROSSING : Kent – Isle of Sheppey

INTEGRATION – Example 2

INTEGRATION – Example 2

PAFA CONSULTING ENGINEERS

1. Risk Analysis – AASHOTO Guidelines1. 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

Objective Hazard Potential

Objectively known

Subjectively realised

Taken into account

Accep

ted R

isk

No

tad

equ

ate

Neg

lected

No

t Realised

No

t kno

wn

Risks modelled

Adequately quantified (good data)

Correct model

Wro

ng

AcceptedRisk

Accurate Risk Assessment

Inaccuracies due to Human Errors

from Faber/Schneider

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.

SRA-QRA-HFA INTEGRATION

http://mar.ist.utl.pt/saferelnet