Scoping Fire Modeling (Task 8)

Task Overview

Background

This step provides simple rules to define and screen fire ignition sources (and therefore fire scenarios) in an unscreened fire compartment.

Purpose

This task has two main objectives:

• To screen out those fixed ignition sources that do not pose a threat to the targets within a specific fire compartment, and
• To assign severity factors to unscreened fixed ignition sources.

It must be noted that only those ignition sources should be considered in this task that were included in establishing the fire ignition frequency in Task 6. All other potential ignition sources that were screened out in Task 6 should neither be addressed in this task. With this task, the level of effort for detailed fire propagation analysis may be reduced. Furthermore, applying severity factors may reduce the compartment frequency calculated in Task 6, resulting in some compartments being screened before detail fire modeling studies are conducted.

Scope

This procedure contains instructions for identifying and screening fixed ignition sources. The procedure also provides some general notes on how to assign severity factor values for ignition sources included in the generic fire frequency model.

The procedure recommends two work forms: (1) the walkdown screening form, and (2) the zone of influence (ZOI) form. The walkdown screening form should be filled during the walkdown. It compiles information about the ignition sources relative to nearby equipment. The ZOI form specifies a zone of influence for ignition sources in a specific compartment.

The focus of this task is twofold.

1. Refine the information about fixed ignition sources. The direct fire effects on fire PRA components or circuits are not addressed. The basic assumption about loss of all fire PRA components (including cables) present in the fire compartment is still maintained in this task. That is, no equipment in the fire PRA component list is screened. Therefore, the location and specific characteristics of the cables carrying fire PRA component-related circuits are not needed for performing this task.
2. Application of severity factors to each ignition source. After applying the severity factor, the compartment fire frequencies calculated in Task 6 are reevaluated.