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Decision Support in Safety Engineering using GRAPIM. Developed by: Patrick Naylor (Health and Safety Executive) In conjunction with Professor A. Taleb Bendiab (School of Computing and Mathematical Sciences Liverpool John Moores University).

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Decision support in safety engineering using grapim

Decision Support in Safety Engineering using GRAPIM

Developed by:

Patrick Naylor (Health and Safety Executive)

In conjunction with

Professor A. Taleb Bendiab

(School of Computing and Mathematical Sciences

Liverpool John Moores University)

Generic Risk And Protection Inspection Model, Realised in the UML


Structure of presentation
Structure of Presentation

  • Overview & Context

  • Application Domain

  • Contribution to Knowledge

  • Reliability & Risk Assessment concepts

  • Why OOSE? Why the UML?

  • The Development Process

  • High Level Overview


What is safety engineering
What is Safety Engineering?

  • Acute Hazards:

  • Identifying Hazard

  • Understanding potential Consequences

  • Estimating probability

  • Putting Protection in place

  • Analyse effectiveness of Protection


What is grapim
What is GRAPIM?

  • Models Risks versus Protection

  • Informs decision on “acceptability”

  • Safety Engineering toolset

  • Structured & systematic methodology

  • Combines assessment and verification

  • Object-Oriented / UML model


Overview the application domain
Overview: The Application Domain

  • Industrial Major Hazards Industries:Petrochemical/Chemical PlantOffshoreNuclear facilities

  • Transport:RailRoadAviation Maritime


Context conditions for grapim
Context: Conditions for GRAPIM

  • Installation

  • Submission

  • Permissioning Regime consisting of: Regulator Duty Holder Risk Owner

  • Rule Set


Contribution to knowledge
Contribution to Knowledge

  • Probabilistic Risk Assessment

  • Reliability Engineering

  • Object-Oriented Software Engineering:application and extension of the Unified Modelling Language (UML)


Key elements
Key elements:

  • Probabilistic Risk Assessment

  • Root & Branch analysis

  • Reliability Engineering



Probabilistic risk assessment
Probabilistic Risk Assessment

R = f.C

Where R is Individual Risk Per Annum (IRPA)

F is frequency of a given event

C is consequence of the given event

In realilty: an event-tree based summation:


Reliability engineering
Reliability Engineering

Defence in GRAPIM with

Probability of Failure on Demand (PFD)

Affords a Risk Reduction Factor (RRF):

RRFGRAPIM= 1/PFD

-3

e.g. a defence with PFD of 1 in 1000 (10 ) affords a risk-reduction factor of 1000.

(Linked closely to the fault-”root” analysis)




Root

and

Branch

Analysis

Model


Criteria
Criteria?

  • Individual Risk Per Annum

  • Tolerability of Risk – 1 in 1000(from the Nuclear Sector)

  • Value of Preventing a Fatality (VPE):£1,000,000 (from R2P2 and DOT)

  • System-based performance standards and specific legislation


The ALARP Triangle

Risk cannot be justified

except in extraordinary

circumstances

Unacceptable Region

1xE-03

The ALARP or

Tolerability Region

(risk is only undertaken

if a benefit is desired)

1xE-05

Broadly acceptable region:

(no need for detailed

working to demonstrate

ALARP)

Negligible

Risk


Probabilistic risk assessment1
Probabilistic Risk Assessment

R = f.C

Where R is Individual Risk Per Annum (IRPA)

F is frequency of a given event

C is consequence of the given event

In realilty: an event-tree based summation:


Reliability engineering1
Reliability Engineering

Defences afford:

Probability of Failure on Demand (PFD)

Risk Reduction Factor (RRF):

RRF= 1/PFD

-3

e.g. a defence with PFD of 1 in 1000 (10 ) affords a risk-reduction factor of 1000.

(Linked closely to the fault-”root” analysis)


Cost-Benefit Analysis:

If D Cost / D Risk Reduction…

<= £1million/life… then viable…

>= £1million/life… then not!

(i.e. must cost no more than £1m to save a life!

… definition of VPE.)


Simplified (Inspection) Lifecycle

Assess Design

Redesign

N

Criteria OK

Y

Verify Operation

Modify Design

&/ Operation

Y

Performs OK

N


Risks versus Protection:

the acceptability test

For all risks and protectors

(with associated RRFs)…

S

N

Risk

RRF

If…

=<

1/1000

1

…then acceptable.


Risk versus Protection:

  • DDoes risk outweigh protection ? (rejection)

  • DDoes protection “outweigh” risk? (acceptance)


Safety integrity level
Safety Integrity Level

SIL is a concept from IEC61508:

(Standard for Computers in Safety Related roles)

SIL = - Log10 (PFD)

=Log10 (RRF)

GRAPIM uses a protection rating system

which uses RRF in preference to SIL


Why object orientation
Why Object-Orientation?

  • Class-Object representation of Installation, Submission and Protection

  • Inheritance

  • Polymorphism

  • Continually changing domain/rulesets could intensify software maintenance


Why the uml
Why the UML?

  • De-facto/pre-eminent language for OOSE

  • Availability of CASE tools (Rational Rose)

  • Associated process (RUP)


Development the rational unified process
Development:The Rational Unified Process

This project deals principally with the elaboration

segment of the process





Activity diagram assessment
Activity Diagram -assessment









Summary
Summary:

  • Safety Engineering – analysis of risks and defences;

  • Define criteria;

  • Construct root and branch model(s);

  • Analyse effect of individual protectors;

  • Do modifications pass CBA test;

  • Analyse bulk effect of protection;

  • If tolerability criteria satisfied – case for safety made.


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