SIL Levels for Fire and Gas systems?

3/2/2011

International Society of Automation Colombia Section

SIL Ratings for SIL Fire & Gas Syst System em Hardware –  A Ques ti on onabl able e Pract ic ice? e?

Paul Gruhn, P.E. Standards Certification Education & Training Publishing Conferences & Exhibits

Bogota

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Where We’re Going… 1. The need for for a new new perform performance ance base based d fire & gas standard 2. Wh What at are are SIL SIL rat rating ings? s? 3. How do do fire fire & gas syste systems ms diff differ er from from safety instrumented systems? 4. Foc Focusin using g on fire fire & gas gas system system hardw hardware are 5. Attent Attention ion must must be paid paid to detec detector tor coverage and mitigation effectiveness

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Current Fire Standards • NFPA 72: National Fire Alarm Code • systems • Both cover fire, not gas systems • Both were developed for commercial applications •

o are prescr p ve, no performance based

Current Gas Standards • ANSI/ISA-12.13.01-2003 •

. .

• Both cover gas, not fire systems • Both were developed for industrial applications • Both are performance based  – In terms of shock, vibration, response to humidity & temperature, drop test, etc., not SIL

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Perfo rmance Standards • IEC 61508: Functional safety of electrical/electronic/programmable electronic safety-related systems • IEC 61511: Functional Safety: Safety Instrumented Systems for the Process Industry Sector

Safety Integrity Levels

Safety Integrity Level

Safety  Availability

Probability of Failure on Demand (PFD)

Risk Reduction Factor (1/PFD)

4

99.99 – 99.999

.0001 - .00001

10,000 – 100,000

3

99.9 – 99.99

.001 - .0001

1,000 – 10,000

2

99 – 99.9

.01 - .001

100 – 1,000

 – 0

. –.

–

 

Control (N/A)

For “Demand Mode” of operation

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Multipl e Layers of Prot ection

Community Emergency Response Fire & Gas Systems Physical Protection (Dikes) Physical Protection (Relief Devices) Safety Instrumented System  Alarms, Operator Intervention

Process

IEC 61511 & Mitig ation

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SIS and F&G Diff erences • Prevention layers (keep it in the pipe) vs. mitigation layers • For SIS: Does a SIL 2 rated sensor, SIL 2 rated logic box, and a SIL 2 rated final element provide a SIL 2 SIF? • Can the same be said for a F&G system?

Event Tree Leak/Fire

Detection Coverage

Hardware Response

Mitigation Effectiveness Yes: P=.9

Yes: P=.99 No: P=.1 Yes: P=.9 X / year  No: P=.01

No: P=.1

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Detector Coverage • Single sensor (1 out of N):  –

• Dual sensor (2 out of N):  – 20% to 90%

• Three or more sensors (3 out of N):  – < 60% or less

• A UK HSE report sites gas detector coverage of 76%

Detector Placement

 A complete walkthrough 3D model of an offshore installation imported into the flame mapping software.

 A view from a flame detector. The circular area represents the actual field of view of the detector.

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Expert vs. Computer 

Expert layout using 9 detectors

Computer layout using 5 detectors

Conclusions 1. Focusing on fire & gas system hardware alone is not the answer  2. Attention must be paid to detector coverage and mitigation effectiveness 3. Techniques are being developed to apply performance based concep s or re gas sys ems

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Thanks To… • ISA 84 committee • • Information presented by Shell, BP and Chevron • Analysis work done by Kenexis

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