LOPA SIL

Module from the Process Safety Management Curriculum curriculum.

Module 3 - LOPA and SIL (IEC 61511) · Learning Objectives · 1. Apply Layers of Protection Analysis (LOPA) for specific scenarios · 2. Compute unmitigated frequency * PFD of IPLs < target TMEL · 3. Credit IPLs: BPCS (0.1), alarm + operator (0.1), relief (0.01) · 4. Determine SIL: SIL 1 (10-100 PFD), SIL 2 (100-1000), SIL 3 (1000-10000) · 5. Verify SIL via reliability calc (1oo2, 1oo3, MTBF, test interval) · Typical IPL Credits (CCPS LOPA)

IPL	PFD	Credit (logs)	Conditions	Notes	Ref
BPCS (single loop, independent)	0.1	1	Independent from initiator	Only one credit	CCPS LOPA
Human response to alarm	0.1	1	Alarm rated, operator trained	Not in the same loop as initiator	CCPS
Relief valve (well-sized, maintained)	0.01	2	ASME coded, tested	Not for fire exposure	CCPS
Rupture disk	0.01	2	Sized correct	One-shot	CCPS
Check valve (well-maintained)	0.1	1	Testing, inspection	Limited credit	CCPS
SIF SIL 1	0.1-0.01	1-2	Fully engineered	IEC 61511	IEC
SIF SIL 2	0.01-0.001	2-3	Fully engineered	Test + diagnostic	IEC
SIF SIL 3	0.001-0.0001	3-4	Redundancy, testing	Rarely needed	IEC
Mechanical interlock	0.01-0.001	2-3	Simple physical	Gravity flow	CCPS

Source: Process_Safety_Management_Curriculum_v1.xlsx · Sheet: LOPA SIL

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