The LOPA process steps in IMS

The LOPA process can be implemented as described below in IMS:

Step 1: Identify the Hazard Scenario: 

Typically, this is part of a HAZOP.

Step 2: Identify the Consequence and Consequence Severity of this Hazard Scenario: 

With an integrated HAZOP/LOPA study, this will be part of a HAZOP. The scenario may be marked for LOPA by the HAZOP team.

Step 3: Identify the Initiating Events of the Hazard Scenario and determine their Frequencies of occurrence. The frequencies can be based on industry-accepted and standards-compliant failure rate data or on site/operational experience: 

IMS has a large failure rate database. When the Consequence is copied from a HAZOP, then its associated Cause is also copied over to the LOPA as the Initiating Event.

Step 4:Identify the Independent Protection Layers (IPLs), i.e., the Barriers, and estimate the Probability of Failure on Demand (PFD) of each:

In IMS the Barriers are categorized as Control Barriers (CB) (SIFs fall in this category), Recovery Measures (RMs), and Conditional Modifiers (CM). In IMS, for many Barriers a template can be selected, where the PFDs have already been defined. (When the Consequence is copied from the HAZOP, then its associated Existing Safeguards are copied over as Barriers.)

Step 5: Calculate the Residual Risk of the Hazard Scenario by mathematically combining the Tolerability Criteria (TC) of the selected Consequence Severity, Initiating Event Frequency, and Barrier PFDs: 

When you click the calculate button in IMS:

• IMS first determines Demand Rate (DR) and Residual Risk (Res), using LOPA principles.
• Then the Tolerability Criteria (TC) is used to determine a Risk Reduction Factor (RRF) for each Consequence category (People, Asset, Community, and Economic). RRF= Res/TC.
• A PFD is then be determined: If RRF>1, PFD = 1/RRF else PFD = 1.
• Based on the IEC 61511 criteria, a Safety Integrity Level (SIL) is then derived from the PFD.
• Lastly an Overall RRF and Overall SIL is determined.

Step 6: Evaluate the Overall SIL to assess the adequacy of the existing or proposed Barriers against the Hazard Scenario.

Step 7: If the Overall SIL for the Consequence is not acceptable, start a SIF Analysis and determine the SIF’s minimum required RRF, i.e., its Target PFD, that achieves an acceptable Overall SIL level.

Step 8: Based on the above results, the LOPA team can provide Recommendation(s) that are specific to the LOPA scenario: 

The Recommendations Summary Tab can be used to record these.