Functional Safety 2016

391 / 1143

ABB Limited
Please reply to: Tel: +44(0)1642 372000 Website: Registration no: Registered Office:
Pavilion 9, Byland Way 3780764 England Daresbury Park
Belasis Hall Business Park Fax: +44(0)1642 372111 E-mail: Daresbury, Warrington
Billingham TS23 4EB VAT Reg No: Cheshire WA4 4BT
United Kingdom 668 1364 13 United Kingdom
To avoid duplication of effort, and enable the delivery of the lifecycle information in a format which is
easy for the operation and maintenance teams to follow, we need use systems which simplify the
recording process and can provide the visual formats such as bow-ties. These formats encourage
operator engagement and enables a clearer understanding of the first 2 questions i.e. the different
hazardous events and the barriers which are in place to protect against it.
The following is an example of a typical LOPA assessment:
Target IL Assessment Summary
Safety impact
Scenario Blockage downstream valve fuel gas scrubber leading 4 times the design
pressure, failure of the vessel and large gas release.
Purpose and Requirement To prevent overpressure detected by PSHH-001 and close XV-001 in 10 sec.
Risk Type Safety Assessment Date dd-mm-yyyy
Consequence Fire and or other explosion, potential for single fatality.
Severity Cd (On-site fatality) Target Frequency 1.0E-6
LOPA Assessment
Initiating Causes
Ref Description Freq(/yr) Tags Justification
A Failure of Control System 0.2 PICA-123 Removed
B Human Error 0.01 SOP-0001 Removed
C Spurious Closure of a Downstream Valve 0.1 Removed
D Blockage of the after filters. F-111A&B Removed
Independent Protection Layers
Ref Description PFDavg Tags Justification
1 BPCS Interlock 0.10000 PIC-123 Removed
2 Operator Response BPCS Alarm 0.10000 PAH-321 Removed
3 Pressure Relief 0.01000 PZV-123 Removed
4 Occupancy 0.10000 Removed
5 Probability of Ignition 0.50000 Removed
PFDavg Calculation
Initiating
Cause
Freq
(yrs)
Independent Protection Layers
1 2 3 4 5 6 7 8 I.E.F(/yr)
A 0.2 1.00000 1.00000 0.01000 0.10000 0.50000 1.0E-4
B 0.01 0.10000 1.00000 0.01000 0.10000 0.50000 5.0E-7
C 0.1 0.10000 1.00000 0.01000 0.10000 0.50000 5.0E-6
D 0.10000 1.00000 0.01000 0.10000 0.50000 0.0E+0
Total Event Frequency Fe/yr. 1.1E-4
PFDavg for Safety Instrumented Function, Ft/Fe 9.5E-3
Safety Integrity Level = SIL 2
To the untrained eye it can be difficult to disseminate the detail contained within this assessment.
However the use of new tools, enable the same information to be automatically represented in a
pictorial view where it becomes clearer of the important of each barrier in protecting against
individual hazardous events and enables operator engagement.