Layers of protection analysis
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Layers of Protection Analysis. ANGELA E. SUMMERS, PH.D., P.E. SIS-TECH Solutions, LLC. We’re Proven-in-Use. W3. W2. W1. -. a. -. C. 1. -. 1. -. a. 1. -. P. 1. 1. 2. -. F. 1. 1. 1. a. P. 2. 2. 3. 1. C. 2. 1. 1. 2. P. 1. 3. 2. 4. F. 2. 2. 1. 3. P. 2.

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Layers of Protection Analysis

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Layers of protection analysis

Layers of Protection Analysis

ANGELA E. SUMMERS, PH.D., P.E.

SIS-TECH Solutions, LLC

We’re Proven-in-Use.


Defining risk tolerance

W3

W2

W1

-

a

-

C

1

-

1

-

a

1

-

P

1

1

2

-

F

1

1

1

a

P

2

2

3

1

C

2

1

1

2

P

1

3

2

4

F

2

2

1

3

P

2

2

4

3

5

3

3

2

F

1

5

6

4

C

3

3

3

4

F

2

6

7

5

4

3

h

C

4

7

8

6

Defining risk tolerance

  • Risk Matrix

  • Risk Graph

  • Quantitative

PFDavg= Ft/Fnp = Tolerable Frequency

Process Demand Frequency


Independent protection layer ipl analysis objective

Independent Protection Layer (IPL) Analysis Objective

Intolerable Risk

  • Drive the consequence and/or frequency of potential incidents to an tolerable risk level

Risk = frequency * consequence

Tolerable Risk


Initiating cause

Initiating Cause

  • Process Deviation

  • Initiating causes

    • Equipment failures

      • instrumentation

      • pumps

      • compressors

    • human errors

    • loss of mechanical integrity

  • Initiating cause frequency


Consequence

Consequence

  • Based on detailed description of hazard scenario.

  • Examine safety, environmental, and economic risks.

  • Often considers the possibility of escaping the incident and the frequency of exposure to the potential incident.

  • Assessment may be qualitative or quantitative (consequence modeling)


Unmitigated risk

Consequence

Unmitigated Risk

Unmitigated Risk

  • Incident Frequency = Initiating Cause Frequency

  • Consequence = Scenario Consequence

Initiating Cause

IS IT TOLERABLE?


Risk tolerance

Risk Tolerance

  • Compare unmitigated risk to risk tolerance.

  • If unmitigated risk is greater than risk tolerance, independent protection layers are required.


What are ipls

What are IPLs?

COMMUNITY EMERGENCY RESPONSE

  • Independent Protection Layers are often depicted as an onion skin.

  • Each layer is independent in terms of operation.

  • The failure of one layer does not affect the next.

PLANT EMERGENCY RESPONSE

MITIGATION

Mechanical Mitigation Systems

Fire and Gas Systems

PREVENTION

Safety Critical Process Alarms

Safety Instrumented Systems

Basic Process Control Systems

Non-safety Process alarms

Operator Supervision

Process Design


Independent protection layer restrictions

Independent Protection Layer Restrictions

  • Sufficiently independent so that the failure of one IPL does not adversely affect the probability of failure of another IPL

  • Designed to prevent the hazardous event, or mitigate the consequences of the event

  • Designed to perform its safety function during normal, abnormal, and design basis conditions

  • Auditable for performance


Layers of protection analysis

IPL

  • IPLs can provide

    • Prevention (active – lower probability)

      • Alarm with operator response

      • Safety Instrumented System

    • Mitigation (active – lower probability/consequence)

      • Pressure relief valve

    • Protection (passive – lower consequence)

      • Dikes

      • Mechanical design

      • Barricades


Mitigated risk reduce frequency only

IPL1

IPL2

IPL3

Mitigated Risk =

reduced frequency * same consequence

Unmitigated Risk = frequency * consequence

PFD1

PFD2

PFD3

Mitigated Risk – Reduce Frequency Only

Key:

Thickness of arrow represents frequency of the consequence if later IPLs are not successful

Impact

Event

frequency


Layers of protection analysis

IPL1

IPL2

IPL3

Mitigated Risk = reduced frequency * same consequence

Unmitigated Risk

Scenario Consequence

Preventive

Feature

Preventive

Feature

Preventive

Feature

REDUCE FREQUENCY TO ACHIEVE TOLERABLE RISK

Success

Safe Outcome

Safe Outcome

Safe Outcome

Initiating Event

Success

Success

Failure

Failure

Consequences exceeding criteria

Failure

Key:

Thickness of arrow represents frequency of the consequence if later IPLs are not successful

Impact

Event

frequency


Layers of protection analysis

PFD=0.1

PFD=0.01

PFD=0.1

Mitigated Risk = reduced frequency * same consequence

Unmitigated Risk

Scenario Consequence

Preventive

Feature

Preventive

Feature

Preventive

Feature

Frequency = 0.9/yr

Safe Outcome

Frequency = 0.099/yr

Safe Outcome

Frequency = 0.0009/yr

Safe Outcome

Success = 0.9

Initiating Event

Frequency = 1/yr

Success = 0.99

Success=0.9

Failure = 0.1

Failure = 0.01

Frequency = 0.0001/yr

Consequences exceeding criteria

Failure= 0.1

Key:

Thickness of arrow represents frequency of the consequence if later IPLs are not successful

Impact

Event

frequency


Mitigated risk reduce frequency and consequence

IPL1

IPL2

CMS1

Mitigated Risk =

reduced frequency *

reduced consequence

Mitigated Risk =

reduced frequency * same consequence

Unmitigated Risk =

frequency * consequence

PFD1

PFD2

PFDN

Mitigated Risk – Reduce Frequency and Consequence

Key:

Thickness of arrow represents frequency of the consequence if later IPLs are not successful

Impact

Event

frequency


Layers of protection analysis

PFD=0.1

PFD=0.1

PFD=0.01

Unmitigated Risk

Mitigated Risk = reduced frequency * reduced consequence

Different Scenario Consequence Occurs

Preventive

Feature

Preventive

Feature

Mitigative

Feature

Frequency = 0.9/yr

Safe Outcome

Frequency = 0.09/yr

Safe Outcome

Frequency = 0.0099/yr

Mitigated Release, tolerable outcome

Success = 0.9

Initiating Event

Frequency = 1/yr

Success = 0.9

Success= 0.99

Failure = 0.1

Failure = 0.1

Frequency 0.0001/yr

Consequences exceeding criteria

Failure = 0.01

Key:

Thickness of arrow represents frequency of the consequence if later IPLs are not successful

Impact

Event

frequency


One sil assignment technique

One SIL Assignment Technique

SIL


Summary

Summary

“A man is rich in proportion to the number

of things he can afford to let alone.”

Henry David Thoreau

Industry will be judged on how it balances the preservation of life and the environment with the need for revenue and profits.

Engineers are charged with

achieving the balance.


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