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Functional Safety Overview
Michael Mats
Table of Contents
What is Functional Safety? FS in Standards FS per IEC 61508 FS Lifecycle FS Certification Process Marketing Activities Additional Resources
Table of Contents
Standards
UL 991 (2004), "Tests for Safety-Related Controls Employing Solid-State Devices" ANSI/UL 1998 (1998), "Software in Programmable Components" (used in
conjunction with UL 991 for products that include software) ANSI/UL 61496-1 (2010), "Electro-Sensitive Protective Equipment, Part 1: General
Requirements and Tests" ANSI/ASME A17.1/CSA B44 (2007), "Safety Code for Elevators and Escalators" EN 50271 (2010), "Electrical Apparatus for the Detection and Measurement of
Combustible Gases, Toxic Gases or Oxygen - Requirements and Tests for Apparatus Using Software and/or Digital Technologies"
IEC 60335-1 (2010), "Household and Similar Electrical Appliances - Safety - Part 1: General Requirements"
IEC 60730-1 (2010), "Automatic Electrical Controls for Household and Similar Use - Part 1: General Requirements"
EN/IEC 61508-1 through -7 (2010), "Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems
Slide 3
Standards
EN/IEC 61511 (2003), "Functional Safety - Safety Instrumented Systems for the Process Industry Sector
EN/IEC 61800-5-2 (2007), "Adjustable Speed Electrical Power Drive Systems - Part 5-2: Safety Requirements - Functional"
EN/IEC 62061 (2005), "Safety of Machinery - Functional Safety of Safety-Related Electrical, Electronic, and Programmable Electronic Control Systems"
EN ISO/ISO 13849-1 (2006), "Safety of Machinery - Safety-Related Parts of Control Systems - Part 1: General Principles for Design"
ANSI/RIA/ISO 10218-1 (2007), "Robots for Industrial Environments - Safety Requirements - Part 1: Robot"
ISO/Draft International Standard 26262 (2009), "Road Vehicles - Functional Safety
Slide 4
Demand Drivers for Functional Safety
Why evaluate your product/system for functional safety? A functional safety assessment determines whether your products meet standards and performance requirements created to protect against potential risks, including injuries and even death Compliance is driven by customer requirements, legislation, regulations, and insurance demands
What is Functional Safety?
What is Functional Safety?
The exact definition according to IEC 61508:
part of the overall safety relating to the EUC and the EUC control system that depends on the correct functioning of the E/E/PE safety-related systems and other risk reduction measures
Slide 6
PresenterPresentation NotesINSTRUCTOR NOTES:
IEC 61508: A standard in seven parts (Parts 1 4 are normative)
1: general requirements that are applicable to all parts.
System safety requirements Documentation and safety assessment
2 and 3: additional and specific requirements for E/E/PE safety-related systems
System design requirements Software design requirements
4: definitions and abbreviations 5: guidelines and examples for part 1 in
determining safety integrity levels, 6: guidelines on the application of parts 2
and 3; Calculations, modeling, analysis
7: techniques and measures to be used To control and avoid faults
Slide 7
PresenterPresentation NotesINSTRUCTOR NOTES:
Indicate that you want to go around the room and want each person to provide this information. Indicate this will be a way for you to get to know the make up of the class.
FS according to IEC 61508: EUC + EUC Control System
EUC + Control System EUC + Control System
EUC + Control System EUC + Control System
Slide 8
PresenterPresentation NotesINSTRUCTOR NOTES:
Indicate that you want to go around the room and want each person to provide this information. Indicate this will be a way for you to get to know the make up of the class.
Why is there something called Functional Safety?
Functional safety as a property has always existed
The definitions of Functional safety show that it is not related to a
specific technology
Functional Safety, as a term and as an
engineering discipline, has emerged with the advancement of complex programmable electronics
Slide 9
PresenterPresentation NotesINSTRUCTOR NOTES:
IEC 61508 mandates an overall safety approach could also be referred to as a:
System safety approach or Holistic approach (accounts also for the whole life cycle of
a system)
Functional safety as per IEC 61508
Slide 10
PresenterPresentation NotesINSTRUCTOR NOTES:EUC: system which responds to input signals from the process and/or from an operator and generates output signals causing the EUC to operate in the desired manner
Overall Safety Lifecycle and E/E/PES life cycle
Slide 11
Concept
Overall Scope Definition
Hazard & Risk Analysis
Overall Safety Requirements
Safety Requirements Allocation
Operation & Maintenance
Safety Validation
Installation & Commissioning
Overall Planning Safety-related systems: E/E/PE Realization:
E/E/PE
Other risk Reduction measures
Overall Modification & Retrofit
Overall Installation & Commissioning
Overall Safety Validation
Overall Operation, Maintenance & Repair
Decommissioning or Disposal
E/E/PES System Safety Requirements Specification
PresenterPresentation NotesINSTRUCTOR NOTES:
Indicate that this is the overall safety lifecycle process found in IEC 61508. Indicate this is a closed-loop process and can be found in several functional safety standards besides 61508. It is a continuous improvement approach in which the designs are reviewed and changed as needed as the process moves along. State that UL has taken this process and generalized it and simplified it.
Functional Safety Certification Process
Kick-Off Meeting
Most effective during the product design phase Collaborate to ensure that the features required by the specified standard are included in the initial design Understand the consequence of choices being made Guidance from certification body on how to design
product Discuss prototyping
Slide 12
Functional Safety Certification Process
Pre-Audit and IA Increase the probability of success of the certification
audit Management system audit Engineers perform on-site GAP analysis Customer received concept evaluation report with
detailed action items
Slide 13
Functional Safety Certification Process
Certification Audit
Certification body audits the systems compliance with the designated standard and functional safety rating
Evaluation of documentation Product is certified
Slide 14
Functional Safety Certification Process
Follow-up Surveillance
A surveillance to verify that the protective functions of the product match the report are
performed Certification body conducts an audit of the
functional safety management system once every three years
Slide 15
Examples of Function Safety Products
Slide 16
EUC E/E/PE System Subsystems Hazard & Risk Analysis shall be conducted for the EUC and the
EUC control system Hazardous events are identified, and the associated risk (the EUC
risk) determined
If the risk is not acceptable, it must be reduced to a tolerable risk level by at least one of, or a combination of, the following: External risk reduction facilities Safety-related control systems, which can be:
Based on electrical/electronic/programmable electronic (E/E/PE) technology
Other technology
Slide 17
PresenterPresentation NotesINSTRUCTOR NOTES:
Necessary risk reduction and Safety Integrity Level (SIL) IEC 61508 is a standard for E/E/PE safety related systems
(E/E/PES), or subsystems. Therefore, the following is addressed by this standard: The part of necessary risk reduction allocated to an E/E/PES is
expressed as a failure probability limit (target failure measure), which in turn is used to select the so called Safety Integrity Level (SIL)
This means SIL is an attribute of an E/E/PES ( or subsystem),
i.e. of a system/device/product that provides risk reduction
Slide 18
PresenterPresentation NotesINSTRUCTOR NOTES:
FS Marks The FS Marks are related to a SIL (or similar other FS ratings)
They can thus only be granted for products or components which provide risk reduction functions (i.e. E/E/PE safety-related systems or subsystems) From a SIL point of view, it doesnt make a difference
whether the E/E/PE safety-related (sub-)system is to be considered a stand alone product or a component
An E/E/PE safety-related system can be:
Either integral part of the EUC control system Or implemented by separate and independent systems
dedicated to safety
Slide 19
PresenterPresentation NotesINSTRUCTOR NOTES:
E/E/PE safety-related system and risk reduction
EUC risk risk arising from the EUC or its interaction with the EUC control system
Tolerable risk
risk which is accepted in a given context based on the current values of society
Necessary risk reduction
risk reduction to be achieved by the E/E/PE safety-related systems, other technology safety-related systems and external risk reduction facilities in order to ensure that the tolerable risk is not exceeded
Residual risk
risk remaining after protective measures have been taken Must be equal or lower than tolerable risk
Slide 20
E/E/PE safety-related system and risk reduction
EUC (+ EUC control system) poses risk, E/E/PES contributes to reduce risk below a tolerable level
IEC 61508-5, Figure A.1
Slide 21
Target failure measure => SIL
EUC Risk
Slide 22
PresenterPresentation NotesOur generic industrial worker is now wondering, this can have a hardware fault, who knows how it was programmed, and did the system integrator really know how the controls worked when he installed them? And he asks himself the famous question, Do I feel lucky?
So we see that there are ma ny possiblilites that lead to faults in safety related circuit so how do we address this?
We can systematically apply risk reduction principles to bring down the risk to a defined level based on established principles.
E/E/PE System and Subsystems
IEC 61508-4, Figure 3
In most cases the FS products certified by UL will be sub-systems of an E/E/PE safety-related system
Subsystem (sensors)
Subsystem (logic unit)
Subsystem (actuators)
Subsystem (data communication)
Slide 23
PresenterPresentation NotesINSTRUCTOR NOTES:
Software Drives FS Requirements - IEC 61508-3
Electromechanical systems are rapidly being replaced by (software) programmable electronic systems due to: Lower cost parts Greater redesign flexibility Ease of module reuse Less PCB space required Improved Efficiency Greater functionality
Slide 24
Software is Being Used Increasingly
Software controls motor-driven equipment safety parameters such as:
- PRESSURE generated by a compressor - Motor SPEED of an inline gasoline pump - POSITIONING of Fuel/Air valves in a
combustion control - FORCE applied by a robotic arm - Air FLOW RATE within a combustion
chamber - the possibilities are limitless
Slide 25
Achieving HW safety integrity
IEC 61508-2 requires application of the following principles to achieve the intended HW safety integrity:
Redundancy
Diversity of redundant channels to eliminate common cause failures
Failure detection per IEC 61508, detection implies a reaction to a safe (operating) state
For fail-safe applications, this can mean activation of the fail-safe state
Reliability of components Probability of dangerous failure (on demand - PFD, per hour - PFH) in
accordance with target failure measure of the required SIL
Slide 26
PresenterPresentation NotesINSTRUCTOR NOTES:
Two routes to demonstrate HW safety integrity: Route 1H and Route 2H Route 1H :
based on hardware fault tolerance and safe failure fraction concepts This means a complete FMEDA on HW component level must be
carried out PFH and SFF calculated on this basis
Route 2H : based on field reliability data and hardware fault tolerance for
specified safety integrity levels, Data must have been recorded in accordance with applicable
standards, >90% statistical confidence stricter HW fault tolerance requirements for the different SILs
Slide 27
PresenterPresentation NotesINSTRUCTOR NOTES:
Slide 28
Achieving HW safety integrity
The primary measurement is PFDavg or PFHavg These depend on the following system-level parameters:
Proof-test interval Mission time (if proof-test not feasible)
In addition to this, the HW integrity of an E/E/PES is measured by
Degree of redundancy: Hardware Fault Tolerance HFT
Detection capability: Safe Failure Fraction SFF Susceptibility to common cause failure: -factor
PresenterPresentation NotesINSTRUCTOR NOTES:
Continue to review the modules titles. Indicate that this course is geared to a general introduction. Point out that the course will be spending a lot of time reviewing the functional safety lifecycle with particular emphasis on the first 2 phases of the process: defining system requirements and Planning and designing requirements Indicate that 61508 not only focuses on software but also other areas. IMPORTANT: State that compliance information is not included in 61508 but ideally you would be able to cross reference to other standards you use.
FMEDA Table (Design level)
Slide 29
Component reference
Component function
Failure modes
Effects failure distribution
Criticality DC [FIT]
D S DD DU Detection reqmts
Exclusion reqmts
R100 energetic separation between channels, cross communication for diagnostics
0,9 1 0,9 0,1 0,813 0.087
short circuit no separation between channels
0,2 1 0,6 0,2 0 0,12 0,08 sample test, off line
MELF resistor
open circuit no cross communication
0,7 1 0,99 0,7 0 0,693 0,007 cross comparison between channels
0,5< value
SFF and diagnostic test interval
Looking at SFF formula, it doesnt depend on
the test frequency (low demand vs high demand)
SFF = (S + DD)/(S + D)
Slide 30
PresenterPresentation Notes7.4.4.1.4 When estimating the safe failure fraction of an element, intended to be used in asubsystem having a hardware fault tolerance of 0, and which is implementing a safetyfunction, or part of a safety function, operating in high demand mode or continuous mode ofoperation, credit shall only be taken for the diagnostics if: the sum of the diagnostic test interval and the time to perform the specified action toachieve or maintain a safe state is less than the process safety time; or, when operating in high demand mode of operation, the ratio of the diagnostic test rate tothe demand rate equals or exceeds 100.
7.4.4.1.5 When estimating the safe failure fraction of an element which, has a hardware fault tolerance greater than 0, and which is implementing a safetyfunction, or part of a safety function, operating in high demand mode or continuous modeof operation; or, is implementing a safety function, or part of a safety function, operating in low demandmode of operation,credit shall only be taken for the diagnostics if the sum of the diagnostic test interval and thetime to perform the repair of a detected failure is less than the MTTR used in the calculationto determine the achieved safety integrity for that safety function.
Simplified approaches proposed by other standards
Also ISO 13849-1 and IEC 62061 suggest simplified methods for determining the probability of random HW failure
ISO 13849-1 approach is based on designated architectures for the different Categories
IEC 62061 approach is based on basic subsystem architectures
These simplified approaches claim to err towards the safe direction, and make a number of assumptions
If the assumptions cannot be made, or if just more precise (and less conservative) values are desired, then more detailed reliability modeling may be applied
Slide 31
PresenterPresentation NotesINSTRUCTOR NOTES:
Additional Information
Websites:
www.ul.com/functionalsafety www.exida.com www.siemens.com http://www.automationworld.com/newsletters_fsn.html
Questions?
Functional Safety OverviewTable of ContentsStandardsStandardsDemand Drivers for Functional SafetyWhat is Functional Safety?IEC 61508: A standard in seven parts(Parts 1 4 are normative)FS according to IEC 61508: EUC + EUC Control SystemWhy is there something called Functional Safety?Slide Number 10Overall Safety Lifecycle and E/E/PES life cycleFunctional Safety Certification ProcessFunctional Safety Certification ProcessFunctional Safety Certification ProcessFunctional Safety Certification ProcessExamples of Function Safety ProductsEUC E/E/PE System SubsystemsNecessary risk reduction and Safety Integrity Level (SIL)FS MarksE/E/PE safety-related system and risk reductionE/E/PE safety-related system and risk reduction Slide Number 22E/E/PE System and Subsystems Software Drives FS Requirements - IEC 61508-3 Software is Being Used IncreasinglyAchieving HW safety integrityTwo routes to demonstrate HW safety integrity:Route 1H and Route 2HAchieving HW safety integrityFMEDA Table (Design level)SFF and diagnostic test intervalSimplified approaches proposed by other standards Additional InformationQuestions?