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Functional Safety DemystifiedBOB WEISS - FUNCTIONAL SAFETY CONSULTANT
IICA TECHNICAL EVENING - 16TH SEPTEMBER 2014
16 September, 2014 1FUNCTIONAL SAFETY DEMYSTIFIED
Purpose
TOPICS
What is Functional Safety?◦ SIS, SIF and SIL
Standards IEC 61508 and IEC 61511
An example to demonstrate compliance
4.5 day TÜV FSEng course in 45 minutes!◦ One day course also available
Explains how to comply with
AS IEC 61511-2004
using a case study
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What is Functional Safety?
Part of Overall Safety◦ freedom from unacceptable risk
Achieved by a Safety Instrumented System (SIS)◦ E/E/PE Safety System in IEC 61508
◦ Examples:
◦ Emergency Shutdown System
◦ Burner Management System
◦ Includes field devices as well as logic solver
A SIS places or maintains a process in a safe state◦ Process = Equipment Under Control (EUC) in IEC 61508
◦ Implements Safety Instrumented Functions (SIFs)
◦ Each SIF achieves a Safety Integrity Level (SIL)
Acronyms to remember: SIS, SIF and SIL !.
16 September, 2014 FUNCTIONAL SAFETY DEMYSTIFIED 3
Why Functional Safety?Buncefield, England 11 Dec 2005
Storage tank level gauge showed constant reading
High level switch left in test mode
Gasoline tank overflowed
Mist exploded◦ largest explosion in peacetime
◦ 20 tanks on fire
◦ burned for three days
◦ significant environmental impact
◦ hundreds of millions of pounds damage
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SIF 1: TZH1234
Safety Instrumented Function - SIF
Basic Terminology
16 September, 2014
SIF 2: PZHH1234
Safety Instrumented System - SIS
Logic Solver(e.g. Safety PLC)
Temperaturetransmitter
Temperaturetransmitter
Pressuretransmitter
Flowtransmitter
Shut-offvalve
Solenoid
Globevalve
Solenoid
Relayin MCC
Component
SIL 2
SIL 1
Safety Integrity Level - SIL
Sensing subsystem Final element subsystemLogic subsystem
Subsystems
FUNCTIONAL SAFETY DEMYSTIFIED 5
Safety Integrity Level vs. Risk Reduction
For Demand Mode SIFs only
16 September, 2014 FUNCTIONAL SAFETY DEMYSTIFIED 6
= 1 / RRF
SafetyAvailability
> 99.99%
> 99.9 ≤ 99.99%
> 99 ≤ 99.9%
> 90 ≤ 99%
Probability of Failureon Demand (PFDavg)
≥ 10-5 < 10-4
≥ 10-4 < 10-3
≥ 10-3 < 10-2
≥ 10-2 < 10-1
SIL
4
3
2
1
Risk ReductionFactor
> 10,000
> 1,000 ≤ 10,000
> 100 ≤ 1,000
> 10 ≤ 100
= 100(1 – PFDavg)= 1 / PFDavg
BPCS* ≤ 10 ≥ 10-1 ≤ 90%
Used to specify SIL achievedUsed to specify SIL required
* Basic Process Control System
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IEC 61508 or IEC 61511
Integrators & users in the process industries can use either IEC 61508 or IEC 61511
IEC 61511 is generally simpler to apply
16 September, 2014 FUNCTIONAL SAFETY DEMYSTIFIED 7
SISdevice
manufacturers
SISintegrators & users
SIL 1-3
SIS integrators &
usersSIL 4
SISintegrators & users
SIL 1-3
for process industries
IEC61508
IEC61511
Safety Lifecycle – IEC 61511
16 September, 2014 FUNCTIONAL SAFETY DEMYSTIFIED 8
Hazard and risk assessment CDV
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessment
and auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
Engineering Contractor
SIS Vendor
End User
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Complying with IEC 61511Target SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Random failure rate (PFDavg)
◦ Architectural constraints (hardware fault tolerance)
◦ Systematic capability for each component◦ Field devices, logic solver, shutdown valves etc.
Not just TÜV certification◦ Though it helps !
Not just meeting PFDavg target.
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Comply Throughout LifecycleFor the rest of the presentation we’ll follow the SIS lifecycle
What do we need to do to comply at each stage?
See the following example…◦ Only the main elements of compliance are covered.
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1 Hazard and Risk Assessment
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Output is a list of hazardous events with their process risk and acceptable risk.
Hazard and risk assessment
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessmentand auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
FUNCTIONAL SAFETY DEMYSTIFIED
A hazard
A “potential source of harm”
300t of Liquefied Petroleum Gas can potentially cause harm
Hazardous Event Example – BLEVE (video)
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300t LPG
P-1
Feed
P-2
Product
PSV-1
LIC
1
FUNCTIONAL SAFETY DEMYSTIFIED
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300t LPG
P-1
Feed
P-2
Product
PSV-1
LIC
1
Identify Hazardous Events: HAZOP
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Node: LPG Tank
Guideword: HIGH LEVEL
Consequence: High Pressure, possible tank rupture & major fire
Existing Controls: Pressure Safety Valve (PSV-1)
New Controls: Add High Level Alarm
H
FUNCTIONAL SAFETY DEMYSTIFIED
RiskThe product of severity and likelihood
“The expected value of loss”
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Consequenceseverity
Likelihood of occurrence
Minor
Medium
Major
LOW HIGHMEDIUM
FUNCTIONAL SAFETY DEMYSTIFIED
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Risk reduction concept
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Overall risk reduction achieved by all means
Residualrisk
Processrisk
Necessary risk reduction
Actual risk reduction
Increasingrisk
Partial risk reductionby SIS
Partial risk reductionby “other means of risk reduction”
Acceptablerisk
FUNCTIONAL SAFETY DEMYSTIFIED
Is risk acceptable ?
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Process under control
Process deviation or disturbance
Process out of control
Hazardous situation
Hazardous event
Impact / Consequence
Level stable
Control valve sticks
Level Increasing
High Pressure
Vessel fails
300t of boiling LPG released -likely major fire and fatalities
PSV
LAH Alarm
Hazard - 300t of LPG
What is risk ?Is it tolerable?
FUNCTIONAL SAFETY DEMYSTIFIED
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Risk Analysis - Layers of Protection
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Mechanical PSV
Alarm LAH
Process
Control System(BPCS)
Hazardous Event !!
Risk Reduction
Hazardous Situation : 1 per y
Target:1 per 10,000y
Required: x 10,000
X 100
Only havex 100 !!
X 1 !
FUNCTIONAL SAFETY DEMYSTIFIED
2 Allocation of Safety FunctionsOften called SIL Assessment, SIL Analysis or SIL Determination
Output is a list of Safety Instrumented Functions together with their required Safety Integrity Level.
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Hazard and risk assessment
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessment
and auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
FUNCTIONAL SAFETY DEMYSTIFIED
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Risk is unacceptable - reduce further
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Process under control
Process deviation or disturbance
Process out of control
Hazardous situation
Hazardous event
Impact / Consequence
Level stable
Control valve sticks
Level Increasing
High Pressure
Vessel fails
300t of boiling LPG released -likely major fire and fatalities
PSV
LAH Alarm
Hazard - 300t of LPG
LZHH Trip
How do wereduce risk further?
FUNCTIONAL SAFETY DEMYSTIFIED
300t LPG
P-1
Feed
P-2
Product
PSV-1
LIC
1
H
LZHH
2
LZT
2
Add a high level trip
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High Level Trip LZHH2 added◦ Shuts off flow when High High level reached
FUNCTIONAL SAFETY DEMYSTIFIED
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Layers of Protection – SIL assessment
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Mechanical PSV
Alarm LAH
Process
Control System(BPCS)
Hazardous Event !!
Risk Reduction
Hazardous Situation : 1 per y
Target:1 per 10,000y
Required: x 10,000
X 100
X 1 !
SIF LZHH
X 100SIL 2
SIF must reduce risk by10,000/100 = 100
FUNCTIONAL SAFETY DEMYSTIFIED
Safety Integrity Level vs. Risk Reduction
For Demand Mode SIFs only
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= 1 / RRF
SafetyAvailability
> 99.99%
> 99.9 ≤ 99.99%
> 99 ≤ 99.9%
> 90 ≤ 99%
Probability of Failureon Demand (PFDavg)
≥ 10-5 < 10-4
≥ 10-4 < 10-3
≥ 10-3 < 10-2
≥ 10-2 < 10-1
SIL
4
3
2
1
Risk ReductionFactor
> 10,000
> 1,000 ≤ 10,000
> 100 ≤ 1,000
> 10 ≤ 100
= 100(1 – PFDavg)= 1 / PFDavg
BPCS ≤ 10 ≥ 10-1 ≤ 90%
Used to specify SIL achievedUsed to specify SIL required
FUNCTIONAL SAFETY DEMYSTIFIED
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Phase 1 & 2 Compliance Achieved !
Target SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ random failure rate (PFDavg)
◦ Systematic Capability of each component
16 September, 2014 23FUNCTIONAL SAFETY DEMYSTIFIED
3 Safety Requirements Specification - SRSDefines functional and integrity requirements of SIS
Output is a set of documents ready for detail design.
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Hazard and risk assessment
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessment
and auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
FUNCTIONAL SAFETY DEMYSTIFIED
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Safety Requirements SpecificationFunctional Requirements
◦ desired behaviour of each SIF
◦ behaviour in response to faults
◦ timing requirements
◦ human machine interface
◦ normal and abnormal modes of operation
◦ bypass requirements
◦ etc.
Safety Integrity Requirements◦ Safety Integrity Level for each SIF
◦ basis for SIL
◦ testing requirements
◦ special requirements to maintain SIL
◦ etc.
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Cause-and-Effect Diagram SIFs commonly documented byCause and Effect diagrams
Should include required SIL somewhere – examples:
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Tag# Description SIF
Instr
um
ent
Range
Trip P
oin
t
Units
CLO
SE
VA
LV
E L
ZV
-02
CLO
SE
VA
LV
E U
V-0
3A
CLO
SE
VA
LV
E U
V-0
3B
OP
EN
S V
ALV
E U
V-0
3C
Set
LIC
1 t
o M
AN
, O
P=
0
BS-01 Burner Loss of Flame 12 ~ ~ X X X
PSL-01 Fuel Gas Pressure Low ~ 7 X X X
LZHH-02 LPG Tank High High Level 13 0-3500 3200 mm 2 0
FUNCTIONAL SAFETY DEMYSTIFIED
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4 Design and EngineeringSIS vendor or contractor for logic solver
EPC contractor or end-user for field hardware
Hazard and risk assessment
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessment
and auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
16 September, 2014 27FUNCTIONAL SAFETY DEMYSTIFIED
Standards Compliance
Target SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ Random failure rate (PFDavg)
◦ Systematic Capability of each component
16 September, 2014 28FUNCTIONAL SAFETY DEMYSTIFIED
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Types of failuresRandom failures – components (“elements”) wear out
◦ use high reliability components
◦ use redundant components
◦ test frequently◦ automated and/or manual
Systematic failures – human error◦ redundant components provide no protection!
◦ “techniques and measures” to◦ avoid faults
◦ detect faults to avoid failures
◦ Functional Safety Management System◦ quality system for functional safety
16 September, 2014 29FUNCTIONAL SAFETY DEMYSTIFIED
Control of systematic failuresFor integration of components into a system (SIS):
◦ Functional Safety Management System (FSMS)◦ for all phases of lifecycle including operation
◦ quality system for SIS
◦ verification, validation, audit and assessment
◦ can comply with either IEC 61511 or IEC 61508
Within each component:◦ ensure quality design in accordance with IEC 61508
◦ ensure appropriate techniques and measures from IEC 61508 used for the SIL of the target SIF
◦ measured by the term “systematic capability”◦ SC 1 to 4 corresponding to SIL 1 to 4
◦ Formerly called “SIL x Capability”
◦ independent certification or “prior use”
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Target SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ Random failure rate (PFDavg)
◦ Systematic Capability of each component
Standards Compliance
16 September, 2014 34FUNCTIONAL SAFETY DEMYSTIFIED
300t LPG
P-1
Feed
P-2
Product
PSV-1
LIC
1
H
LZHH
2
LZT
2
SIL Verification
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Does the design of SIF LZHH2 meet SIL 2?
SIL 2
FUNCTIONAL SAFETY DEMYSTIFIED
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Hardware Fault Tolerance“Architectural constraints” in IEC 61508
Aim is to avoid unrealistic reliability claims◦ from single components
IEC͏ 61508-2 (Route 1H) constrains SIF architecture based on:◦ Safe Failure Fraction
◦ complexity of device (“Type A” or “Type B”)
◦ target SIL
Outcome is required minimum Hardware Fault Tolerance (HFT)◦ no. of voted devices minus no. required to perform safety function
◦ For MooN architecture, HFT = N - M
Use Tables in IEC 61508 part 2◦ or use Route 2H
◦ or use IEC 61511 simplified requirements◦ these are subject to significant change in the forthcoming 2nd edition
16 September, 2014 36FUNCTIONAL SAFETY DEMYSTIFIED
Safe Failure FractionBlock valve, normally open & normally energized
In case of an out of control process, the valve has to close
Closesspontaneouslydue to lossof energy
SAFE
Undetected
Detectedby diagnostics
Undetected
Detectedby voltage control
DANGEROUS
Stuck atopen
SFF
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Architectural Constraints – IEC 61508-2
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Type A Subsystems e.g. pressure switches
Safe Failure Fraction
Hardware Fault Tolerance
0 1 2
< 60% SIL 1* SIL 2* SIL 3*
≥ 60 < 90% SIL 2 SIL 3 SIL 4
≥ 90 < 99% SIL 3 SIL 4 SIL 4
≥ 99% SIL 3 SIL 4 SIL 4
Type B Subsystems e.g. logic solver, smart transmitters
Safe Failure Fraction
Hardware Fault Tolerance
0 1 2
< 60% Not allowed SIL 1 SIL 2
≥ 60 < 90% SIL 1* SIL 2* SIL 3*
≥ 90 < 99% SIL 2 SIL 3 SIL 4
≥ 99% SIL 3 SIL 4 SIL 4
Table 2
Table 3
* IEC͏ 61511-2003
HFT forfield devices
For MooNN-M = HFT
FUNCTIONAL SAFETY DEMYSTIFIED
300t LPG
P-1
Feed
P-2
Product
PSV-1
LIC
1
H
LZHH
2
LZT
2
Case Study: Architectural Constraints
Transmitter LZT 2 is a smart radar gauge
Can we use single transmitter to satisfy SIL 2?
Must also check for logic solver and valve
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Type B Subsystems e.g. logic solver, smart transmitters
Safe Failure Fraction
Hardware Fault Tolerance
0 1 2
< 60% Not allowed SIL 1 SIL 2
≥ 60 < 90% SIL 1* SIL 2* SIL 3*
≥ 90 < 99% SIL 2 SIL 3 SIL 4
≥ 99% SIL 3 SIL 4 SIL 4
Case Study: Architectural ConstraintsSmart Transmitter = Type B device
◦ use Table 3 in IEC 61508-2
Safe Failure Fraction = 91%◦ from certificate
For SIL 2, required Hardware Fault Tolerance = 0
Therefore one transmitter is ok for SIL 2
LTZ 2
16 September, 2014 40FUNCTIONAL SAFETY DEMYSTIFIED
Standards Compliance
Target SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ Random failure rate (PFDavg)
◦ Systematic Capability of each component
16 September, 2014 41FUNCTIONAL SAFETY DEMYSTIFIED
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300t LPG
P-1
Feed
P-2
Product
PSV-1
LIC
1
H
LZHH
2
LZT
2
SIL Verification
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What is calculated “PFDavg” for SIF LZHH-2?
SIL 2
FUNCTIONAL SAFETY DEMYSTIFIED
Safety Integrity Level vs. Risk Reduction
For Demand Mode SIFs only
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= 1 / RRF
SafetyAvailability
> 99.99%
> 99.9 ≤ 99.99%
> 99 ≤ 99.9%
> 90 ≤ 99%
Probability of Failureon Demand (PFDavg)
≥ 10-5 < 10-4
≥ 10-4 < 10-3
≥ 10-3 < 10-2
≥ 10-2 < 10-1
SIL
4
3
2
1
Risk ReductionFactor
> 10,000
> 1,000 ≤ 10,000
> 100 ≤ 1,000
> 10 ≤ 100
= 100(1 – PFDavg)= 1 / PFDavg
BPCS ≤ 10 ≥ 10-1 ≤ 90%
Used to specify SIL achievedUsed to specify SIL required
FUNCTIONAL SAFETY DEMYSTIFIED
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Case Study: PFD CalculationTest interval = 1 y
Reliability data:◦ Valve: λDU = 1/10y (= 0.1 y-1)
◦ Logic solver: λDU = 1/1000y (= 0.001 y-1)
◦ Sensor: λDU = 1/100y (= 0.01 y-1)
PFDavg = λDU x TI / 2= 0.1 x 1 / 2 = 0.05 for valve
0.001 x 1 / 2 = 0.0005 for logic solver0.01 x 1 / 2 = 0.005 for transmitter
Total PFDavg = 0.05 + 0.0005 + 0.005 = 0.0555
Calculated SIL = 1 (PFDavg range 0.01 – 0.1)
Required SIL = 2 Not OK!
How can this be fixed?
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LZHH
2
LZV 2
LZT
2
FUNCTIONAL SAFETY DEMYSTIFIED
Case Study: Adjust Test IntervalTest interval = 1 month
Reliability data:◦ Valve: λDU = 1/10y (= 0.1 y-1)
◦ Logic solver: λDU = 1/1000y (= 0.001 y-1)
◦ Sensor: λDU = 1/100y (= 0.01 y-1)
PFDavg = λDU x TI / 2= 0.1 / 12 / 2 = 0.004 for valve
0.001 / 12 / 2 = 0.00004 for logic solver0.01 / 12 / 2 = 0.0004 for transmitter
Total PFDavg = 0.004 + 0.00004 + 0.0004 = 0.00444
Calculated SIL = 2 (PFDavg range 0.001 – 0.01)
Required SIL = 2 OK
BUT operations object to monthly testing !
16 September, 2014 45
LZHH
2
LZV 2
LZT
2
FUNCTIONAL SAFETY DEMYSTIFIED
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Case Study: Duplicate Block ValvesTest interval = 1 year
Reliability data:◦ Valve: λDU = 1/10y (= 0.1 y-1)
◦ Logic solver: λDU = 1/1000y (= 0.001 y-1)
◦ Sensor: λDU = 1/100y (= 0.01 y-1)
For 2 valves 1oo2 voting: PFDavg = 0.0033 (was 0.05)
PFDavg = 0.0033 + 0.0005 + 0.005 = 0.0088
Calculated SIL = 2 (PFDavg range 0.001 – 0.01)
Required SIL = 2 OK
LZHH
2
LZV 2A
LZT
2
LZV 2B
16 September, 2014 46FUNCTIONAL SAFETY DEMYSTIFIED
Standards ComplianceTarget SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ random failure rate (PFDavg)
◦ Systematic Capability of each component.
How likely is it that each component is free from systematic faults (“bugs”) ?
16 September, 2014 47FUNCTIONAL SAFETY DEMYSTIFIED
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Control of systematic failuresFor integration of components into a system (SIS):
◦ functional safety management system◦ for all phases of lifecycle including operation
◦ verification, validation, audit and assessment
◦ can comply with either IEC 61511 or IEC 61508
Within each component:◦ ensure quality design in accordance with IEC 61508
◦ ensure appropriate techniques and measures from IEC 61508 used for the SIL of the target SIF
◦ measured by the term “systematic capability”◦ SC 1 to 4 corresponding to SIL 1 to 4
◦ formerly called “SIL Capability”
◦ independent certification or “prior use”
16 September, 2014 48FUNCTIONAL SAFETY DEMYSTIFIED
Case Study: Transmitter SelectionMust control systematic faults
Transmitter selected must comply with IEC 61508 and IEC 61511
Must either:
be designed and manufactured in accordance with IEC 61508◦ confirmed by independent certificate (e.g. by a “TÜV” or exida)
◦ Systematic Capability from 1 to 4◦ i.e. techniques and measures are suitable for SIL 1 to 4
OR
meet requirements for Prior Use (or “proven in use”):◦ sufficient experience gained in a comparable application
Best practice: require BOTH prior use and certification
16 September, 2014 49FUNCTIONAL SAFETY DEMYSTIFIED
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Component CertificationAn independent organisation certifies that the component meets the requirements of IEC 61508 for a particular SIL
◦ not only “TÜV” !!!
Parts 2 and 3 contain numerous “techniques and measures” required to avoid and control faults
◦ the rigour required increases with SIL
The aim is to reduce the likelihood of systematic faults to an acceptably low level relative to the SIL
The result is expressed as “Systematic Capability” or SC from 1 to 4◦ corresponding to SIL 1 to 4
◦ was previously called “SIL Capability”
The certificate also usually also includes failure data and whether the component is “Type A” or “Type B”
◦ details are in a companion report
16 September, 2014 50FUNCTIONAL SAFETY DEMYSTIFIED
Transmitter TÜV Certificate
16 September, 2014 51FUNCTIONAL SAFETY DEMYSTIFIED
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Transmitter TÜV Certification
16 September, 2014 52FUNCTIONAL SAFETY DEMYSTIFIED
Prior Use (IEC 61511)Requires that appropriate evidence is available that the component is suitable based on consideration of:
◦ the manufacturer’s quality systems
◦ adequate identification of the devices
◦ demonstration of performance in similar operating environments
◦ the volume of operating experience
Focus is on demonstrating freedom from systematic faults
IEC 61508 term is “Proven in Use”◦ more rigorous requirements
16 September, 2014 53FUNCTIONAL SAFETY DEMYSTIFIED
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Standards ComplianceTarget SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ random failure rate (PFDavg)
◦ Systematic Capability of each component
Design now complies
16 September, 2014 54FUNCTIONAL SAFETY DEMYSTIFIED
5 Installation, Commissioning, ValidationLogic Solver installed with field equipment
Includes loop checking, validation and final functional safety assessment.
Hazard and risk assessment
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessment
and auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
16 September, 2014 55FUNCTIONAL SAFETY DEMYSTIFIED
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Standards ComplianceTarget SIL must be specified for each SIF based on hazard and risk analysis
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ random failure rate (PFDavg)
◦ Systematic Capability of each component
Verification, Validation, Functional Safety Assessment
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Case Study: Verification and ValidationProject Verification and Validation Plan required
◦ Consider level of independence required (i.e. independent engineer)
◦ Define responsibilities
Verify each phase e.g.◦ Safety Requirements Specification◦ Verify hardware design documents◦ Verify functional specifications etc◦ Implement code walkthrough
Logic Solver Factory Acceptance Test ◦ Complete integration test validates application software on target hardware
Logic Solver Site Acceptance Test◦ Power up test on site
Safety Function Testing◦ SIS validation
Functional Safety Assessment
Note that terminology is from the ISO9000 discipline◦ Some disciplines swap the meanings of “verification” and “validation”!
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6 Operations, Maintenance and ModificationThe Cinderella Phases !
User must follow a Functional Safety Management System for the life of the SIS.
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Hazard and risk assessment
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessment
and auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
FUNCTIONAL SAFETY DEMYSTIFIED
Ops and Maintenance ObligationsTrain operators & maintainers
Proof test each SIF at specified interval
Monitor design assumptions◦ demand rates
◦ component reliability
Adjust test interval to suit
Control modifications
Ensure Maintenance and Operational Overrides are used as designed
Monitor and promptly follow-up diagnostics
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300t LPG
P-1
Feed
P-2
Product
PSV-1
LIC
1
H
LZHH
2
LZT
2
Case Study: Operation and MaintenanceRisk analysis assumed:
◦ demand on SIF once per year
◦ what happens in practice?
SIL verification assumed:◦ transmitter failure rate 0.01 y-1
◦ what happens in practice?
Etc etc . . .
Must verify actual performance against assumptions and adjust testing as required
Documentation of assumptions is critical
Mechanical: PSV
SIF: LZHH
AlarmLAH
Process
Control System(BPCS)
Hazardous Event !!
Risk Reduction
Hazardous Situation
Target:1 per 10,000y
Required: X 10,000
X 100
X 100SIL 2
1 per y
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Summary 1 – The SIS Lifecycle
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Hazard and risk assessment
Allocation ofsafety functions
to protection layers
Design andengineering of
safety instrumented system
Installation, commissioningand validation
Operation and maintenance
Modification
Decommissioning
Design anddevelopment
of other meansof risk reduction
Safety requirementsspecification for the
safety instrumented system
Managementof functional
safety andfunctional
safetyassessment
and auditing
Safetylife-cyclestructure
andplanning
Verification
10 11
5
6
7
8
4
3
1
2
9
Engineering Contractor
SIS Vendor
End User
FUNCTIONAL SAFETY DEMYSTIFIED
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Summary 2 – RequirementsTarget SIL must be specified for each SIF based on hazard and risk assessment
Processes for SIS throughout lifecycle must comply
Each SIF must meet target SIL requirements for:◦ Hardware Fault Tolerance (architectural constraints)
◦ random failure rate (PFDavg)
◦ Systematic Capability of each component.
Not just TÜV certification◦ though it helps !
Not just meeting PFDavg target
Don’t forget spurious trip rate!
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Need more?IICA runs the following courses:
ISA One-day Introduction to SIS◦ runs periodically or on request
TÜV Rheinland Functional Safety Engineer course◦ NEW!! from March 2015
◦ For those with 3+ years experience in functional safety
◦ Leads to Functional Safety Engineer (TÜV Rheinland) qualification
If interested please email [email protected]
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Questions?
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