understanding sil
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Training Session - Lunch and Learn
Understanding Safety Integrity Level (SIL)Dinesh Vijay Bhurke
13th March 2014
Why Safety ? Basic Concepts, Definitions, Acronyms SIL concept Standards – IEC, ISA Layer of Protection concept Risk Management SIL Assignment /Assessment (Risk Reduction)
Hazard Matrix method Risk Graph method LOPA method
Content
2Training: Lunch & Learn Session
Why Safety ?
3Training: Lunch & Learn Session
Chernobyl, Nuclear Power Plant, April 1986
Piper Alpha Platform, July 1986
Bhopal Gas Leak disaster
WORLD’s WORST INDUSTRIAL DISTASTERS
Why Safety ?
4Training: Lunch & Learn Session
WORLD’s WORST INDUSTRIAL DISTASTERS
Source: Emerson’s PlantWeb University, SIS 103 - Safety Standards.
28 aprile 2023
Pres..bozza.. 5
Introduction
Freedom from unacceptable risk.
Per Year Per YearOccupation Staying at homeChemical Industry 5 in 1,00,000 Electrocution 1.2 in 10,00,000Mining(Coal) 2 in 10,000
TravelInvoluntary Air(Scheduled) 2 in 10,00,000Lightining 1 in 100,00,000 Train 3 in 10,00,000Fire 2 in 1,00,000 Car 2 in 10,000Run over 6 in 1,00,000 Motor Cycle 2 in 100
Fatality Rates
What is Risk? Frequency of occurrence of harm X Severity of that harm.
Risk without any Protection
Tolerable Risk
CONSEQUENCES
FRE
QU
EN
CY
Reduction
Why Safety?
What is Safety ?
6
People Outside Plant
People Inside Plant
Environment
Assets Corporate Image
Off-Spec Production
Safety Vs. Availability
• SIL: Safety Integrity Level• SIF: Safety Instrumented Function• SIS: Safety Instrumented System (ESD)• SFF: Safe Failure Fraction = (ƛs+ ƛdd)/ (ƛs+ ƛdd+ ƛdu)• SRS: Safety Requirements Specification• STR: Spurious Trip Rate• RRF: Risk Reduction Factor• PFD: Probability of Failure on Demand• PFDavg, SIF: Probability that the SIF fails to respond to a Process Demand
(PFDavg, SIF = PFDsensor + PFDlogic solver + PFDFE + PFDpower supply)
• MTTF: Mean Time To Failure (e.g. 76 yrs)• MTTR: Mean Time To Repair (e.g. 1 month)• MTBF: Mean Time Between Failure (= MTTF + MTTR)• ALARP: As Low As Reasonably Practicable• IPL: Independent Protection Layer• FMEA: Failure Mode and Effect Analysis• FTA: Fault Tree Analysis• LOPA: Layer of Protection Analysis• HAZOP: Hazard and Operability Analysis
Acronyms
7Training: Lunch & Learn Session
Understanding Safety Integrity Level (SIL)
• What does SIL mean?– Safety Integrity Level – A measure of probability to fail on demand(PFD) of the SIS.– It is statistical representation of the integrity of the SIS when a
process demand occurs.– A demand occurs whenever the process reaches the trip
condition and causes the SIS to take action.– There are 4 SIL levels. SIL Levels are measures of how we
achieve function safety.– Applies to the complete safety function/loop– Higher SIL means Stricter requirements. Safety Function fails less and thus plant protection is available more.
8Training: Lunch & Learn Session
Understanding Safety Integrity Level (SIL)
• SIL is how we measure the performance of safety functions carried out by safety instrumented systems
• SIL must be viewed from 3 perspectives– Process Owners Which Safety function do I need and how much do I need?– Engg. Companies, System Integrators, Product Developers How do I Build SIL compliant safety devices, function or systems?– Plant Operators How do I operate, maintain and repair safety functions and systems to maintain identified SIL levels?
9Training: Lunch & Learn Session
SIL STANDARDS
10Training: Lunch & Learn Session
IEC-61508 (1998 & 2010)
IEC-61511 (2003)
ISO 26262
ISA S84 (1996 & 2004)
IEC 62279
EN 50128
Generic Used By Vendors
Industry Specific-Used by Designers & End users.
Process Industry
Automotive Railways
Calls Safety system as E/E/PES
Calls Safety system as SIS
IEC-61513
Nuclear
IEC 62061
Machinery
ESD/HIPPS/BMS/FGS
SIL Classification
SIL Probability Category
1 1 in 10 to 1 in 100
2 1 in 100 to 1 in 1,000
3 1 in 1,000 to 1 in 10,000
4 1 in 10,000 to 1 in 100,000
1 in 10 means, the function will fail once in a total of 10 process demands
1 in 1000 means, the function will fail once in a total of 1000 process demands
11Training: Lunch & Learn Session
SIL Classification
SILLevel Risk Reduction Factor
SIL 4 >=10-5 to <10-4 >=0.00001 to <0.0001 100000 to 10000
SIL 3 >=10-4 to <10-3 >=0.0001 to <0.001 10000 to 1000
SIL 2 >=10-3 to <10-2 >=0.001 to <0.01 1000 to 100
SIL 1 >=10-2 to <10-1 >=0.01 to <0.1 100 to 10
Probability of failure on demand (Demand Mode of Operation)
Safety Integrity Levels
12Training: Lunch & Learn Session
Concept of Layers of Protection
13Training: Lunch & Learn Session
Concept of Layers of Protection
14Training: Lunch & Learn Session
Concept of Layers of Protection
15Training: Lunch & Learn Session
Multiple Initiators tripping one Final Element
Initiators
Final Element
SIF-1
SIF-2
SIF-3
Logic Solver
16Training: Lunch & Learn Session
One Initiator tripping multiple Final Elements
Logic Solver
Initiator
Final Elements
SIF-1
SIF-2
SIF-3
17Training: Lunch & Learn Session
1 A
B2
SensorsFinal Control
Elements
LogicSolver
SIF 1
C3SIF 2
D4SIF 3
5 E
F6
SIF 4
Overall Safety Instrumented System showing SIFs
18Training: Lunch & Learn Session
Risk Management
19Training: Lunch & Learn Session
Three important steps• Identify Hazards / Hazardous events• Analyze /Assess the Hazards/Hazardous events• Reduce risk where necessary
Assigning the SIL with Hazard Matrix
20Training: Lunch & Learn Session
Assigning the SIL – Risk Reduction
21Training: Lunch & Learn Session
Assigning the SIL – Risk Reduction
22Training: Lunch & Learn Session
Assigning the SIL – Risk Reduction
23Training: Lunch & Learn Session
24
Assigning the SIL – Risk Reduction
25
Assigning the SIL with Risk Graph
Training: Lunch & Learn Session
Risk reduction with LOPA
26Training: Lunch & Learn Session
27
Risk reduction with LOPA
Training: Lunch & Learn Session
Thank You
28
Suggestions / Feedback
29
There could be a next session ……1. Introduction to Functional Safety.2. Hardware Design.3. SIL Verification methods.
Strictly on popular demand
Suggestions / Feedback
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