Uncontrolled Hydrocarbon Release — Fault Tree
A worked process-safety fault tree for loss of primary hydrocarbon containment from a pipeline or process system. Aligned to IEC 61511 at SIL 2 for the SIS protection layer, with API RP 754 Tier 1 incident classification.
The scenario
Hydrocarbon release from primary containment is the canonical "Loss of Primary Containment" (LOPC) event in upstream and downstream oil & gas operations. The top event of this fault tree is uncontrolled release of flammable or toxic hydrocarbon inventory from a pipeline or process system above the API RP 754 Tier 1 reporting threshold — release magnitudes that, on ignition, can escalate to flash fire, vapour cloud explosion, or BLEVE.
Top event and decomposition
The top OR gate captures the three release mechanisms that LOPA studies typically extract from a HAZOP for a hydrocarbon-containing system:
- Pipeline / vessel integrity failure — internal corrosion, external SCC, third-party damage (excavator strike), or fatigue. Each leaf draws λ from RBI inspection data, OREDA, or PARLOC.
- Overpressure rupture — process upset combined with the AND of (BPCS pressure controller fails) AND (SIS pressure trip fails) AND (PSV fails to lift). The SIS branch is sized to a SIL 2 PFD per IEC 61511 Clause 11.
- Joint / fitting failure — flange-gasket blow-out, valve-stem packing failure, sample-port operation error. Joint failure rates from EI-RBI generic data.
The Beta-factor CCF block models common-cause between BPCS and SIS where they share instrument air, signal cabling, or are mounted on the same skid.
Standards alignment
This template is the deliverable that LOPA + FTA produce together for an IPL containing flammable/toxic inventory: LOPA establishes the SIL target; FTA decomposes the SIS implementation across initiators, sensors, logic-solvers and final elements; importance ranking on the cut sets directs inspection and proof-test planning. The output integrates into the SRS per IEC 61511 Clause 10 and the inspection plan per API RP 580/581.
Use this template
Open in FTA Studio, override the generic component λ values with your facility-specific inspection data and proof-test history, run MOCUS to identify dominant cut sets, and (Enterprise edition) layer Monte Carlo over the leaf λ distributions to produce the lognormal mean and 95th-percentile expected by SIS verification reports.