2.-Introduction-to-Safety-Instrumented-System-SIS
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Questions and Answers

What is the primary purpose of a Safety Instrumented System (SIS)?

  • To automate all plant operations
  • To increase the level of risk in the plant
  • To bring the plant to a safe state from a hazardous state (correct)
  • To reduce the need for operator intervention

    • In case the Basic Process Control System (BPCS) fails, what layer of protection is required?

  • Layer 1
  • Layer 4
  • Layer 2 (correct)
  • Layer 3

    • What does IEC define a Safety Instrumented System (SIS) as?

  • A system that controls minor plant adjustments
  • A system that monitors operator performance
  • A system that ensures continuous plant operation
  • A system used to implement Safety Instrumented Functions (correct)

    • Why are Safety Instrumented Systems (SIS) considered critical in industrial plants?

    <p>To respond to hazardous plant conditions</p> Signup and view all the answers

    What is the main function of a Safety Instrumented System (SIS) in an industrial plant?

    <p>To bring the plant to a safe state from a hazardous state</p> Signup and view all the answers

    Why are Safety Shutdown Systems categorized as part of a Safety Instrumented System (SIS)?

    <p>To protect equipment and personnel during hazardous situations</p> Signup and view all the answers

    What is the purpose of a Logic Solver in a safety instrumented system?

    <p>Execute pre-programmed actions based on sensor information</p> Signup and view all the answers

    Which characteristic is essential for a Logic Solver in a safety instrumented system?

    <p>Fast decision-making ability</p> Signup and view all the answers

    What does a Final Controlling Element (FCE) do in a safety instrumented system?

    <p>Implements the action determined by the logic system</p> Signup and view all the answers

    Why is it important for a Final Controlling Element (FCE) to comply with 'Fail Safe' requirement?

    <p>To ensure safe operation even in case of failure</p> Signup and view all the answers

    What happens when a fail-closed valve vents all actuating air pressure?

    <p>The valve fails closed</p> Signup and view all the answers

    Which component blocks air pressure and vents the actuating diaphragm when de-energized?

    <p>Solenoid valve</p> Signup and view all the answers

    What is the purpose of Safety Instrumented Functions (SIF) in a Safety Instrumented System (SIS)?

    <p>To achieve or maintain a safe condition of the process</p> Signup and view all the answers

    What does SIL stand for in the context of Safety Instrumented Systems?

    <p>Safety Integrity Level</p> Signup and view all the answers

    Why does an Oil Refinery typically have a higher SIL requirement compared to a water treatment plant?

    <p>Oil Refineries have higher levels of risk associated with their processes</p> Signup and view all the answers

    What is the main emphasis when determining the Safety Integrity Level (SIL) target for Safety Instrumented Functions (SIF)?

    <p>Achieving or maintaining a safe condition of the process</p> Signup and view all the answers

    Which part of an Industrial Safety Instrumented System (SIS) is responsible for detecting abnormal process conditions?

    <p>Sensor &amp; Transmitter</p> Signup and view all the answers

    What do Safety Instrumented Systems (SIS) aim to achieve when referring to 'when demanded' performance?

    <p>Performance specifically when needed</p> Signup and view all the answers

    What is the purpose of Layer 5 - Passive Protection Layer?

    <p>To reduce the impact on the process/plant environment during severe conditions</p> Signup and view all the answers

    What are examples of structures that belong to the Passive Protection Layer?

    <p>Tank Bund Walls, Fire Walls</p> Signup and view all the answers

    In the context of plant protection layers, what is the function of Layer 4?

    <p>Actively protecting against over-pressurization</p> Signup and view all the answers

    Who primarily makes up the Plant Emergency Response Team (Layer 6)?

    <p>Different representatives from management, operations, and maintenance departments</p> Signup and view all the answers

    When does the Emergency Response Team (Layer 6) come into action?

    <p>After all other protection layers fail</p> Signup and view all the answers

    What is the purpose of a Common Alarm System in a system?

    <p>To provide audible and visual alarms for notification purposes</p> Signup and view all the answers

    Which layer is responsible for bringing the process in a safe condition during severe plant conditions and failure of the Safety Instrumented System (SIS)?

    <p>Layer 4 - Active Protection Layer</p> Signup and view all the answers

    How does Relay Logic differ from Electronic Logic in implementing a Safety Instrumented System (SIS)?

    <p>Relay Logic uses relays and contacts, while Electronic Logic performs logical operations on logic inputs.</p> Signup and view all the answers

    Why is testing Safety Instrumented Systems (SIS) considered important?

    <p>To uncover any Functional, Potential, or Hidden failures</p> Signup and view all the answers

    What does an Active Protection Layer mainly consist of?

    <p>Devices that bring the process into a safe condition during failures</p> Signup and view all the answers

    What function does a Pressure Relief Valve serve in the Active Protection Layer?

    <p>To relieve moderate changes in tank pressure</p> Signup and view all the answers

    Study Notes

    Safety Instrumented System (SIS)

    • SIS uses dedicated sensors and transmitters to detect abnormal process conditions, with response time and precision being crucial characteristics.
    • SIS controllers (logic solvers) determine the action to be taken based on the information gathered from sensors and execute pre-programmed actions to prevent hazards.

    Logic Solver (LS)

    • A logic solver must be able to render a fast decision and comply with the "Fail-Safe" condition.
    • It is typically a PLC or Relay Logic that reads signals from sensors and executes pre-programmed actions.

    Final Controlling Element (FCE)

    • A Final Controlling Element must have the correct Valve Flow Coefficient (Cv) and comply with the "Fail Safe" requirement.
    • It implements the action determined by the logic system.

    Support System

    • Provides necessary utilities for the system to operate, such as 24VDC, A/S, H/S, etc.

    Common Alarm System

    • Provides an audible and visual alarm for notification purposes, which must be loud and bright to be heard and seen by control room personnel.

    Methods of Implementing a SIS Logic Solver

    • Using Relay Logic
    • Using Electronic Logic

    Importance of Testing SIS

    • Testing is crucial to uncover any Functional, Potential, or Hidden type of failure.
    • It affects the Safety Integrity Level (SIL) of the system.

    Layers of Protection

    • Layer 1: Basic Process Control System (BPCS)
    • Layer 2: BPCS + Operator Intervention
    • Layer 3: Safety Instrumented System (SIS)
    • Layer 4: Active Protection Layer
    • Layer 5: Passive Protection Layer
    • Layer 6: Plant Emergency Response Layer

    Layer 3: Safety Instrumented System (SIS)

    • Defined by IEC as an Instrumented System used to implement one or more Safety Instrumented Functions (SIF).
    • Examples: Critical Control Systems, Safety Shutdown Systems, Instrument Protective Function (IPF), Equipment Protection Systems, Emergency Shutdown Systems (ESD), Safety Critical Systems, and Safeguarding Systems.

    Function of SIS

    • Brings the plant to a safe state from a hazardous state.
    • Designed to respond to industrial plant conditions that may be hazardous or have hazardous consequences.

    Safety Instrumented Functions (SIF)

    • A function implemented by SIS aimed at achieving or maintaining a safe condition of the process by referring to a specific hazardous event.
    • Each SIF must be designed and tested to meet the SIL target.

    Other Layers of Protection

    • Layer 4: Active Protection Layer (e.g. Pressure Relief Valve, Pressure/Vacuum Valve)
    • Layer 5: Passive Protection Layer (e.g. Tank Bund Walls, Fire Walls, Oil Contaminated Sewerage System)
    • Layer 6: Plant Emergency Response Layer (e.g. Emergency Response Team)

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