Hazardous Operated Safety Instrumented Systems

1
Hazardous Operated Safety Instrumented Systems
2
Introduction

• Within a modern industrial society, automation
  technology is definitely a key factor for
  success.
• A long time very conservative environment, namely
  safe automation technology, has been strongly
  changing over the last two decades towards fully
  electronic control and automation systems.

3
Introduction

• The requirements for safety-related automation
  system are as essential as the normative
  requirements.

4
Agenda

• Basics of Functional Safety
• Fault Avoidance Basis and Measurement
• Hazard Analysis
• Project Approach

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Key Words

• SIS
• SIL
• HAZOP
• Redundancy
• Voting
• Device integrity
• Diagnostics

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Basics of Functional Safety

• History of development
• For nearly 20 years, great effort has been made
  in developing National, European und
  International standards for control engineering.
  In the early 1980s the International
  Electrotechnical Commission (IEC) and the German
  Institute of Standardization (DIN) investigated
  the fundamental requirements for protective
  systems using measurement and control techniques.
• In 1991, the IEC developed a holistic standard
  encapsulating full life cycle concepts and titled
  Functional Safety of Electrical/Electronic/Progra
  mmable Electronic Safety-Related Systems
  (IEC61508).

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Basics of Functional Safety

• Fundamental considerations
• .
• The most important contributor is the
  specification of how the system should operate,
  implemented by the engineer or the programmer.
• The next major factor is modifications after
  commissioning, operation and maintenance, as the
  end user often does not understand the intent of
  the original design and safety engineering.
• Measures must be taken to prevent or minimize
  such errors in a safety systems development
  and/or design phase.

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Basics of Functional Safety

• Fundamental considerations
• For the original manufacturer of safety related
  systems, the standards DIN V VDE 0801 and IEC
  61508 differentiate between measures for fault
  avoidance during the development stage and fault
  control of the final product.
• Fault avoidance procedures in designing
  electronics are implemented by the manufacturer
  and verified by a test organization such as the
  German test institute Technischer
  Überwachungsverein (TÜV).
• These measures are applied during planning,
  development and manufacturing such that errors
  can be detected and corrected. The measures for
  fault control are part of the system hardware and
  software functionality and result in an
  appropriate safety-related action

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Basics of Functional Safety

• Fault Avoidance Basis and Measurement
• The aim is to avoid errors from the very
  beginning using constructive and analytical
  processes along with testing and verification
  procedures throughout the overall safety life
  cycle.
• IEC 61508 describes the individual phases of the
  safety life cycle prescribing fundamental
  requirements for each phase.

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Basics of Functional Safety

• Fault Avoidance Basis and Measurement
• The safety-related reliability of complex safety
  systems can be only achieved by implementing
  rigorous and analytic processes which incorporate
  continual verification and testing procedures. .
• Required risk reduction may be achieved by
  combining technical and non technical methods,
  with the result that the remaining (residual)
  risk of the hazardous plant or equipment is
  reduced to an acceptable level

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Project Approach

• The project approach is an
• up-to-date international area of interest,
  using high-tech product and technologies
  constant evolving.

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Project Approach

• Protection Layers
• Layers of protection can be used to reduce
  unacceptable risk to an acceptable level. The
  amount of risk reduction for each layer is
  dependent on the specific nature of the safety
  risk and the impact of the layer on the risk.
  Economic analysis should be used to determine the
  appropriate combination of layers for mitigating
  safety risks.

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Project Approach

• SIS Factors
• The scope of an SIS is restricted to the
  instrumentation or controls that are responsible
  for bringing a process to a safe state in the
  event of a failure. The availability of an SIS is
  dependent upon
• Failure rates and modes of components
• Installed instrumentation
• Redundancy
• Voting
• Diagnostic coverage
• Testing frequency

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Project Approach

• SIL Factors
• A SIL can be considered a statistical
  representation of the availability of an SIS at
  the time of a process demand. A SIL is the test
  of acceptable SIS design and includes the
  following factors
• Device integrity
• Diagnostics
• Systematic and common cause failures
• Testing
• Operation
• Maintenance

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Project Approach

• Hazard Analysis
• Hazard and Operability Studies (HAZOP) is a
  technique (almost like brainstorming) whereby a
  group of well informed people aim to identify all
  the ways in which hazards may appear in a system.
• Its purpose is to-
• Establish hazardous failure modes, and
• A measure of their effect by a systematic
  examination of the system and its components.

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Project Approach

• Hazard Analysis
• HAZOP is applicable at all stages of the system
  lifecycle although it is of limited use until a
  relatively detailed description of the system has
  been developed.
• Typically the selected members of the HAZOP team
  will have had previous experience of such
  systems, and complement one another (are from
  different backgrounds) so that the benefits of
  the team approach are apparent.

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Project Approach

• Hazard Analysis
• A disciplined and systematic approach is adopted
  to ensure there are no obvious omissions.
• Each component of the system and each hazard is
  considered in turn.
• The team employs a series of guidewords and
  variables to facilitate the process.
• Questions arise about the design and these act as
  the basis of the formulation of solutions to
  mitigate the hazards that are identified.

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Project Approach

• Hazard Analysis
• Example in use of guidelines
• in analysing pipelines in a chemical plant, the
  guidewords-
• NO LESS MORE
• could be applied to the variables
• FLOW PRESSURE TEMPERATURE
• to identify possible hazards.

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Project Approach

• Hazard Analysis
• The basis (paperwork or model of the system) of
  the activity must be accurate.
• The HAZOP process for a large system may take
  several months - each major component is
  typically considered in turn.
• A database of previous disasters can be used as a
  reminder of options to be looked at.
• It is possible for the team to get 'carried away'
  and install expensive equipment to compensate for
  possible hazards.
• Proposals for change should go through the HAZOP
  process.

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Project Approach

• Risk identification process-summary
• A summary of the risk identification process may
  be as follows-
• use Preliminary Hazard Analysis techniques at the
  appropriate stage of development
• use the HAZOP process
• use Fault Tree Analysis for situations where
  control is involved or a service has to be
  provided
• Use carefully monitored design