IEC 61511 introduction

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Functional Safety - IEC 61511 Introduction
New Plymouth, 11 April 2013
Koen Leekens
+65 977 9547

Copyright exida Asia Pacific © 2013 AsiaPacific@exida.com
What is…?
Today’s Objective
Introduce the Concept and Basic Principles of IEC 61511

Safety is Only as Strong as its Weakest Link
exida

exida History
Founded in 1999 by experts from Manufacturers, End Users,
Engineering Companies and TÜV Product Services
“Independent provider of Tools, Services and Training
supporting Customers with Compliance and Certification to
any Standards for Functional Safety, Cyber Security and Alarm
Management”
Rainer Faller
Former Head of TÜV Product Services
Chairman German IEC 61508
Global Intervener ISO 26262 / IEC 61508
Author of several Safety Books
Author of IEC 61508 parts
Dr. William Goble
Former Director Moore Industries
Developed FMEDA Technique (PhD)
Author of several Safety Books
Author of several Reliability Books

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handbook on
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data
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exida Customers (extract from 2000+)

What is…?
Functional Safety:

What do accidents teach us?
Buncefield 2005
Bhopal 1984 Flixborough1974
Seveso 1976

Primary Cause of Failures?
Specification
Changes after
Commission
Operation and
Maintenance
Design and
Implementation
Installation and
Commission

Primary Cause of Failures?
Specification
Changes after
Commission
Operation and
Maintenance
Design and
Implementation
Installation and
Commission
Source Health, Safety & Environmental Agency
The majority of accidents are:
… Preventable if a systematic
Risk-Based Approach is adopted…
More than
80% of Failures
Before Startup

Device Manufacturers - Sector Specific Not Available
Which Standard?
IEC 61513
Nuclear
IEC 61511
Process Industry
IEC 61508
Functional Safety for E/E/PES Safety Related Systems
ISO 26262
Road Vehicles
End Users - Systems Integrators
IEC 62061
Machinery

Relationship IEC 61508 – IEC 61511
Manufacturers and Suppliers of
Devices
IEC 61508
Safety Instrumented System
designers, Integrators and users
IEC 61511
Process Sector Safety Instrumented System Standards

RANDOM
Failures
IEC 61511 – Protection Against:
SYSTEMATIC
Failures
Random Failures? Systematic Failures?

Random Failures: “Usually a permanent failure due to a
system component loss of functionality – hardware related
What are…?

Systematic Failures: “Usually due to a design fault, wrong
specification,not fit for purpose , error in software program,
...
What are…?

Question?
Is Redundancy sufficient protection against SYSTEMATIC
FAILURES?

RANDOM
Failures
IEC 61508 – Protect Against:
SYSTEMATIC
Failures
HOW? HOW?

RANDOM
Failures
SYSTEMATIC
Failures
Probabilistic
Performance Based
Design
HOW?

PROBABILISTIC BASED DESIGN

RANDOM
Failures
SYSTEMATIC
Failures
Probabilistic
Performance Based
Design
Detailed Engineering
Process

Key Aspects of IEC 61508/61511
Safety Integrity Levels (SIL)
– Reliable Hardware with predictable failure rates to
protect against Random Failures (Physical)
Safety Lifecycle
– Safety Management with controlled and systematic
processes to protect against Systematic Failures (Design)

The IEC 61511 Safety Lifecycle

Management and
Planning
Analysis Phase
Realization Phase
Operate and Maintain

Management and
Planning

Industry Competency Program
www.cfse.org

Analysis Phase

SRS Always Required?
Do I Need
A SIS in
My Plant?

IEC 61511/61508 are Risk Based
“Is it worth going for the Cheese?”

What is…?
Risk: Consequence x Likelihood.
Accounts for both the consequense and the likelihood portion
of the risk

Analyze Process Risk
(Inherent Risk)
Tolerable Level of Risk
Risk
Risk Analysis
(defined by Customer per application)
High
Low

(Inherent Risk)
Risk
Risk Analysis
Define Tolerable
Risk
High
Low

What is…?
Tolerable Risk: The level of risk that society will accept
– Who is being exposed to risk?
 Individuals
 Society
 Environment
– What is the nature of the risk?
 Fatality / Injury
 Permanent / Temporary Damage
 Financial Loss
MoralLegal
Financial

What is…?
ALARP: As Low As Reasonably Practicable

Tolerable Risk Sample – Statistics UK
Activity Probability per
person per year
Travel
Air 2 x 10 -6
Train 3 x 10 –6
Bus 2 x 10 -4
Car 2 x 10 –4
M otorcycle 2 x 10 -2
O ccupation
Chemical Industry 5 x 10 –5
M anufacturing
Shipping 9 x 10 –4
Coal M ining 2 x 10 –4
Agriculture
Boxing
Voluntary
Rock climbing 1.4 x 10 –4
–3

(Inherent Risk)
Risk
Risk Analysis
Analyze Actual
RISK
High
Low

Design Changes
Calculated Process Risk
(Inherent Risk)
Risk
Risk Analysis
High
Low

Design Changes
Other Risk Reduction
(Inherent Risk)
Risk
Risk Analysis
Analyze other Layers of
Protection
High
Low

(Inherent Risk)
Risk
Bring Risk below
Tolerable
Risk Analysis
Design Changes
High
Low

(Inherent Risk)
Risk
SIL is measure for
Risk Reduction
Risk Analysis
Design Changes
High
Low

Risk Reduction Factor (RRF) and SIL
High Risk
Low Risk
1/RRF =
PFD

1/RRF =
PFD

Safety Requirements Specification
• Target SIL
• Functional Description of Each SIF
• Response Time
• Bypass Requirement
...
( IEC 61511-1 clause 10)

Realization Phase

SIF Design
The SIL achieved is the minimum of:
1. SILPFD:Probability of Failure on Demand Average/per hour (PFDAVG /PFH)
2. SILAC : Hardware Fault Tolerance
3. SILCAP:Capability to prevent Systematic Failures (SILCAP)

Probability of Failure on Demand
1. SILPFD:Probability of Failure on Demand Average/per hour (PFDAVG /PFH)
2. SILAC : Hardware Fault Tolerance
3. SILCAP:Capability to prevent Systematic Failures (SILCAP)
PFDsensor + PFDmux + PFDinput + PFDmp + PFDOutput + PFDrelay + PFDfe + PDFprocess-connection

S SD SU
SAFE DETECTED
SAFE UNDETECTED
DANGEROUS
UNDETECTED
DANGEROUS
DETECTED
D DD DU
60%
40%
Divide each failure rate into specific failure modes
IEC 61508-6 Method

What is…?
Fail Danger: A failure that prevents the safety function from
performing
Fail Safe: Anything that is not Fail Danger
.
NOTE: Definitions refer to single channel architectures.

What is…?
Hardware Fault Tolerance: The quantity of failures that can
be tolerated while maintaining the safety function
Architecture
Hardware
Fault
Tolerance
1oo1 0
1oo1D 0
1oo2 1
2oo2 0
2oo3 1
2oo2D 0
1oo2D 1
1oo3 2

What is…?
Safe Failure Fraction: A measurement of the likelihood of
getting a dangerous failure that is NOT detected by
automatic self diagnositcs
.
NOTE: Definitions refer to single channel architectures.

IEC 61508 Safe Failure Fraction
SFF =
SD + SU + DD
SD + SU + DD + DU
= 1 -
DU
Total

Example FMEDA 3051S

Example 3051S
Hardware Fault Tolerance: The quantity of failures that can
be tolerated while maintaining the safety function
Architecture
Hardware
Fault
Tolerance
1oo1 0
1oo1D 0
1oo2 1
2oo2 0
2oo3 1
2oo2D 0
1oo2D 1
1oo3 2

Certified versus Proven in Use
Certificate
by
Independent
Assessor
Justification
by User

Product Certification
Functional safety certification for devices is accomplished
per IEC 61508
Products are certified to a Safety Integrity Level (SIL)
The result is typically a certificate and a certification report
SIL Certification
Vendor showed
sufficient protection
against Random and
Systematic Failures

Example…
1. SILPFD: SIL2
2. SILAC : SIL1
3. SILCAP: SIL3
The SIL level for this
Safety Instrumented
Function (SIF) is:
???

Example
1. SILPFD: SIL2
2. SILAC : SIL1
3. SILCAP: SIL3
The SIL level for this
Safety Instrumented
Function (SIF) is:
SIL1

Operate and Maintain

What is…?
Proof Testing: A manually initiated test designed to detect
failure of any part of a SF. Different proof test procedures can
have different levels of effectiveness.
No practical proof
test will detect all
failures

“Disabled” Safety is not SAFE!
www.securityincidents.org
revents Safety Shutdown
opriate Control
on system used Microsoft Excel on a PC
orkstation also had Norton anti-virus
are prevented the proper communications
stem. A safety shutdown that should have
Incident with “Certified” Boiler
Anti-Virus Software
Prevents Safety Shutdown
Source www.securityincidents.org

“Disabled” Safety is not SAFE!
www.securityincidents.org
revents Safety Shutdown
opriate Control
on system used Microsoft Excel on a PC
orkstation also had Norton anti-virus
are prevented the proper communications
stem. A safety shutdown that should have
Explosion of “Certified” Boiler
Anti-Virus Software
Prevents Safety Shutdown
Source www.securityincidents.org
Advanced Technology
introduces
new THREATS?

exida Functional Integrity Certification™
Functional Integrity Certification™
Functional Safety Certification ™
+
Functional Security Certification ™
“Integrity is doing the right thing,
even if nobody is watching.”
(Anonymous)

Thank You

IEC 61511 introduction

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