---
title: "Methodology Step 4"
slug: "methodology-step-4"
updated: 2026-10-27T23:11:38Z
published: 2026-10-27T23:11:38Z
canonical: "ims-handbook.cenosco.com/methodology-step-4"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://ims-handbook.cenosco.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Methodology Step 4

## ![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/SRBI%20(2)(1).jpg?sv=2026-02-06&spr=https&st=2026-10-28T13%3A49%3A12Z&se=2026-10-28T14%3A49%3A12Z&sr=c&sp=r&sig=xkjMZ7l2MyFb5SmRJUFFErwk37CMbznkKmAnMOUPtX8%3D)

Step 4 Determine the most Credible Failure Scenario:

Below the Step 4 Methodology is described. See also [](/v414/docs/software-step-1)[](/v414/docs/software-step-3)[Software Step 4](/v414/docs/software-step-4).

---

The credible failure scenario should be established by the RBI team. They should consider the expected DM, process conditions, the Equipment design, operating history, and inspection history.

A complete failure scenario should describe the failure itself (left-hand side of the [bowtie](/v414/docs/degradation-management-theory-overview)), the top event, and the Barriers on the right-hand side of the bowtie. In general, this would include a description of:

- The failure location (on Equipment)
- The [hole size](/v414/docs/hole-size-for-consequence-assessment)
- The [leak rate](/v414/docs/release-rate-calculations)
- The products leaked (their flammability [Nf factor] and toxicity [Nh factor)
- The formation of liquid pool or gas cloud
- Ignition sources (e.g., auto ignition, no ignition sources, road presence, etc.)
- The location where leaked liquid will go to (e.g., oil containing sewer, surface water, soil)
- Detection of the leak
- Presence of people

An example of a Credible Failure Scenario is: “*50 bar methane gas leak from 6 mm hole, containing < 1000 ppmw H2S at 60°C at approx. 650 kg/h forming a flammable gas cloud in semi-congested area without ignition sources. Unit down time for temporary repair 2 days*.”

## Specific Guidance Summary

[Guidance per Special Emphasis](/v414/docs/special-emphasis-components) gives additional information with regards to Special Emphasis Components (see the table below).

Specific guidance summary - Credible Failure Scenario:

| DM / *Special Emphasis Component* | Description |
| --- | --- |
| [*Pressure Relief Devices*](/v414/docs/pressure-relief-devices-rvrdvb) | For PRVs, define the Failure on Demand Scenarios. |
| [*Tanks*](/v414/docs/tanks) | If planning to do Load Case calculations, then fill in the required Specs needed for the Load Case 1 calculations (see [Tank Equipment](/v414/docs/tank-equipment)). |
|  |  |
|  |  |