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    Basic Lopa and Sil

    Uploaded by

    Brian Dunagan
    Layer of Protection Analysis (LOPA) is a technique used to determine the frequency of unwanted events by analyzing independent protection layers (IPLs). The probability of failure on demand (PFD) of each IPL is used to calculate the overall frequency. A Safety Integrity Level (SIL) is assigned based on the risk reduction needed and is inversely related to the PFD - a higher SIL indicates a lower allowed PFD. A SIL is selected by first analyzing risks, then using LOPA to quantify likelihood and consequences, and determining the SIL needed to reduce risk to as low as reasonably practicable.

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    Basic Lopa and Sil

    Uploaded by

    Brian Dunagan
    694 views9 pages
    Layer of Protection Analysis (LOPA) is a technique used to determine the frequency of unwanted events by analyzing independent protection layers (IPLs). The probability of failure on demand (PFD) of each IPL is used to calculate the overall frequency. A Safety Integrity Level (SIL) is assigned based on the risk reduction needed and is inversely related to the PFD - a higher SIL indicates a lower allowed PFD. A SIL is selected by first analyzing risks, then using LOPA to quantify likelihood and consequences, and determining the SIL needed to reduce risk to as low as reasonably practicable.

    Original Description:

    Description of SIL and LOPA process

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    Layer of Protection Analysis (LOPA) is a technique used to determine the frequency of unwanted events by analyzing independent protection layers (IPLs). The probability of failure on demand (PFD) of each IPL is used to calculate the overall frequency. A Safety Integrity Level (SIL) is assigned based on the risk reduction needed and is inversely related to the PFD - a higher SIL indicates a lower allowed PFD. A SIL is selected by first analyzing risks, then using LOPA to quantify likelihood and consequences, and determining the SIL needed to reduce risk to as low as reasonably practicable.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    694 views9 pages

    Basic Lopa and Sil

    Uploaded by

    Brian Dunagan
    Layer of Protection Analysis (LOPA) is a technique used to determine the frequency of unwanted events by analyzing independent protection layers (IPLs). The probability of failure on demand (PFD) of each IPL is used to calculate the overall frequency. A Safety Integrity Level (SIL) is assigned based on the risk reduction needed and is inversely related to the PFD - a higher SIL indicates a lower allowed PFD. A SIL is selected by first analyzing risks, then using LOPA to quantify likelihood and consequences, and determining the SIL needed to reduce risk to as low as reasonably practicable.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 9

    Layer of Protection Analysis (LOPA)

    & Safety Integrity Level (SIL) Selection


    What is LOPA?
    LOPA (Layer of Protection Analysis) is a form
    of event tree analysis used to determine the
    frequency of an unwanted event, which can be
    prevented by one or more protection layers.
    Initiating
    Event
    IPL #1
    Fails
    IPL #2
    Fails
    IPL #3
    Fails
    IPL #1
    Success
    IPL #2
    Success
    IPL #3
    Success
    Event
    Ends
    Event
    Ends
    Event
    Ends
    How is the Frequency of a Consequence Calculated?
    Probability of Failure on Demand (PFD) is used
    to quantify the likelihood of a given
    consequence with the layers in place.
    Initiating
    Event
    0.5/yr.
    IPL #1
    0.2
    IPL #2
    0.07
    IPL #3
    0.3
    IPL #1
    Success
    IPL #2
    Success
    IPL #3
    Success
    Event
    Ends
    Event
    Ends
    Event
    Ends
    Frequency = 0.5 x 0.2 x 0.07 x 0.3 = 2.1 x 10
    -3
    Event PFD
    Operator
    Response
    0.2
    PRV
    Activation
    0.07
    Ignition 0.3
    Typical Protection Layers

    Basic Process Control System

    Operator Intervention

    Use Factors

    Mechanical Integrity of Vessels and Piping

    Physical Relief Device

    External Risk Reduction Facilities

    Ignition Probabilities

    Explosion Probabilities

    Occupancy Factors
    What is an IPL?
    Independent Protection Layers (IPL) are
    incident protection layers that must meet the
    following criteria:

    Specificity An Independent protection layer
    must be specifically designed to be capable of
    preventing the consequence(s) under
    consideration.

    Independence The protection layer must
    operate completely independently of all other
    protection layers; no common equipment may
    be shared between layers.

    Dependability The layer must be able to
    dependably prevent the consequence(s).

    Auditability The layer should be proof tested
    and maintained.
    What is a SIL?
    A Safety Integrity Level (SIL) is the overall
    availability of a ESD Safety Instrument
    Function (SIF) or an ESD system component
    calculated as 1 minus the sum of the
    average probability of failure on demand
    (PFD).

    SIL RRF (risk
    reduction
    factor)
    PFD Safety
    Availability
    0/a Process Control
    1 10-100 10%-1% 90%-99%
    2 100-1000 1%-.1% 99%-99.9%
    3 1000-10000 .1%-.01% 99.9%-99.99%
    What is a SIF and a SIL?
    A Safety Instrumented Function (SIF) is
    an action a Safety Instrumented System
    (SIS) takes to bring the process or
    equipment under control to a safe state.
    A Safety Instrumented System (SIS) is a
    collection of sensors, logic solvers, and
    actuators that executes one of more
    safety instrumented functions (SIFs)
    that are implemented for a common
    purpose.
    NOTE: The SIL classification belongs
    to the individual SIF, not the entire SIS.
    When a piece of equipment is common
    to multiple SIFs, it must be designed to
    meet the highest SIL classification
    found amongst those individual SIFs!
    Identifying a SIF
    A Safety Instrumented Function (SIF) is
    an action a Safety Instrumented System
    (SIS) takes to bring the process or
    equipment under control to a safe state.
    1. The SIF must signal or indicate a
    hazardous condition is present and
    harm will result if there is no action.

    2. The function should execute or
    facilitate some action to achieve a
    safe state.

    3. A safe state should result from the
    function for this process.
    How is a SIL Selected?
    1. Determine the level of risk that exists after
    considering all non-SIS related mitigation
    measures (relief valves, dikes, passive fire
    protection, etc.)

    2. Risk scenarios are typically identified through
    HAZOPs or similar risk assessments.

    3. LOPA is used to quantify the likelihood and
    consequence and to identify protection layers
    (IPLs and non-IPLs)

    4. Each additional SIL step reduces the likelihood
    of a given consequence by an order of
    magnitude.
    Example: Baseline risk is 10
    -2
    per year, a
    SIL 3 system reduces the overall likelihood
    by 3 orders of magnitude to 10
    -5

    5. Risk should be reduced to ALARP.

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