EIT IDC Safety Instrumentation SILS Rev2

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Basic understanding of sil

Text of EIT IDC Safety Instrumentation SILS Rev2

  • 31/07/2013

    1

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    Safety Instrumentation including Safety

    Integrity Levels (SILs)

    by

    Steve Mackay

    www.eit.edu.au

    EIT Micro-Course Series Every two weeks we present a

    35 to 45 minute interactive course

    Practical, useful with Q & A throughout

    PID loop Tuning / Arc Flash Protection, Functional Safety, Troubleshooting conveyors presented so far

    Go to http://www.eit.edu.au/free-courses

    You get the recording and slides

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    Safety Instrumentation including SILs

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    It cant possiblyhappen to us ..

    Where are we now .Safety wise

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    Flixborough, England, June 1, 1974: "It was a still, warm, sunlit afternoon. One moment the teacups were tinkling and the kettles whistling. The next moment, a blast of nightmarish intensity as the giant plant blew up and blotted out the sun."--Humberside Police Report

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    Safety Instrumentation including SILs

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    Nypro Chemical Works

    Flixborough, UK1 June 1974

    Cyclohexane vapour cloud

    ignitedBlast equivalent to

    15 tons of TNT28 killed

    CAUSE:

    Faulty temporary piping design by poorly qualified design teamAccident led to the Control of Industrial Major Accident (CIMAH) Regulations- now superseded by COMAH.

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    MilanSeveso

    LOMBARDY

    Icmesa, Seveso,

    Italy10 July 19761976

    Trichlorophenol (TCP) is anintermediate used to producethe disinfectant hexachlorophene.Unexpected exothermic reaction causedpressure build-up and release of Dioxin by-product.198341 barrels containing the toxic residues gomissing and are eventually found and incinerated in late 19851995Civil lawsuits still proceeding

    Lombardy

    Resulted in the Seveso I Directive that has influenced much subsequent legislation.

    CAUSE:Management failure by all parties in the post-accident phase

    EIT and IDC Technologies - Webinar Slides

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    Three Mile Island,Pennsylvania28 March 1979#2 ReactorNo deaths or injuries

    The term cognitive overload was born. Raised awareness of HMI issues.

    CAUSE:Inadequate control room instrumentation and poor emergency response

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    Bhopal

    Bhopal, IndiaUnion Carbide3 December 1984Dangerous chemical reaction occurredwhen a large amount of water got intothe MIC storage tank #610

    Exothermic reaction exploded the storage tank

    40 tons of methyl isocyanatespread for 2 hours 8km down windover the city of 900,000 inhabitants

    More than 3,800 died and 11,000 disabled

    CAUSE: Management Failures + Disabled safety systemsResulted in several governments passing legislation that required better accounting and disclosure of chemical inventories

    EIT and IDC Technologies - Webinar Slides

    Safety Instrumentation including SILs

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    Milford Haven, UK

    24 July 1994

    Texaco refinery

    Refer to the HSE report on this incident - ISBN 0 7176 1413 1

    CAUSE: Operators lacked adequate information on which to make decisions following an earlier incident. Contribution from Alarm Overload

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    Sonat Exploration Company

    (Now El Paso Production

    Co.)Louisiana, 4 March 1998Catastrophic Vessel over-

    pressurisation4 killedCAUSE:

    Maloperation of the plant, no plant operating procedures, inadequate vessel relief devices, and absence of any process hazard analysis (PHA) on the original plant design.

    Source Chemical Safety and Hazard Investigation Board

    EIT and IDC Technologies - Webinar Slides

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    BP Refinery, Texas City, Tx : 23 March 2005During the startup of the Isomerization Unit on Wednesday, March 23, 2005, explosions and fires occurred, killing fifteen and harming over 170 persons in the Texas City Refinery, operated by BP Products North America Inc.

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    BP Refinery, Texas City Tx: 23 March 2005

    It cant possiblyhappen to us ?

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    Safety System Basics:

    The Safety Instrumented SystemGeneral abbreviation: SIS

    AKA: Trip system, shutdown system, instrumented protection system (IPS)

    The SIS is an example of aFunctional Safety System

    Meaning: Safety depends on the correct functions being performedFunctional safety: Part of the overall safety relating to the process

    and the BPCS which depends on the correct functioning of the SIS and other protection layers. (IEC 61511 clause: 3.2.25)

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    Hardware components of a control loop

    Input devices(e.g. sensors /transmitters)

    Output devices/ final elements(e.g. valves)

    PLC/Controller

    EIT and IDC Technologies - Webinar Slides

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    Process Control versus Safety

    ControlSeparation of safety controls from process controls

    ProtectionSystem

    OperatingEquipment

    ControlSystem

    DCS

    SIS

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    (Hardware and Software)

    Logic solver

    Sensor Logic Solver Actuator

    Scope of a Safety Instrumented System

    EIT and IDC Technologies - Webinar Slides

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    Definition of a Safety Instrumented System

    LogicSolver

    Sensors

    SIS UserInterface

    Basic Process Control System

    Actuators

    3 Sub-systems: Each subsystem must meet SIL target

    Fig 1.3

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    Safety System Basics All types of safety measures are

    intended to reduce risk of harm to people, the environment and assets.

    The risks are due to the presence of HAZARDS: Hazardous Process or Procedure

    HAZARD: An Inherent physical or chemical characteristic that has the potential for causing harm to people, property or the environment

    EIT and IDC Technologies - Webinar Slides

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    What Is Hazard and What Is Risk?Hazard

    An inherent physical or chemical characteristic that has the potential for causing harm to

    people, property, or the environment.

    RiskThe combination of the severity and probability

    of an event.

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    Simple Shutdown System: Example 1

    Basic tank level control with overflow hazard

    PSV

    FluidFeed

    Vapour Hazard

    LT1

    LC1

    I/P

    FC

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    Simple Shutdown System

    LT1

    PSV

    LC1

    I/P

    FC

    FluidFeed

    FC

    Logic Solver

    LT2

    LAHH2

    AS

    HS2Reset

    LI2

    Tripped Alarm

    Fig 1.4

    FC = fails closed on loss of air pressure

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    Stage 1 Trip

    Plant Emergency Shutdown Command

    Stage 1 low level

    Stage 1 high pressure

    Stage 2 Trip

    Stage 2 high level

    Stage 2 high temperature

    Time delay Stage 3 Trip

    Stage 3 high level

    Stage 3 tripped

    Typical multiple stage plant trip and ESD system

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    Risk reduction: the fast bowlerIf we cant take away the hazard we shall have to reduce the risk

    Reduce the frequency and /or reduce the consequence

    Example: Brett Lee is the bowler: He is the HazardYou are the batsman: You are at riskFrequency = 6 times per over. Consequence = Ouch!

    Risk = 6 x Ouch !

    Risk reduction: Limit bouncers to 2 per over. Wear more pads.

    Risk = 2x ouch !

    Fig 1.5

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    Measurement of RiskQualitative: High, Low, Moderate

    An effective measure if we all have the sameunderstanding of the terms

    Quantitative: 1 in 10 years x 5 people hurt

    Effective if you can guess the numbers

    EIT and IDC Technologies - Webinar Slides

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    Risk = Frequency of Event x Consequence

    Fatal Serious injury

    Minor injury

    Risk

    Consequences

    Frequency

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    To Reduce Risk: Reduce Frequency or Consequence or do both

    Fatal Serious injury

    Minor injury

    RiskFrequency

    Consequences

    EIT and IDC Technologies - Webinar Slides

    Safety Instrumentation including SILs

  • 31/07/2013

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    Risk Reduction: Design Principles

    Hazard Identified

    Risk Reduction Requirement

    Tolerable Risk Established

    Safety Function DefinedSIL Target Defined

    Risk Estimated/Calculated

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    SIS

    OperatingEquipment

    ControlSystem

    Safety Control systems act independently of the process or its control system to try to prevent a hazardous event.

    EIT and IDC Technologies - Webinar Slides

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    The SIS achieves risk reduction by reducing the frequency (likelihood) of

    the hazardous event

    SI

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