Page 176 - CHEF Guide

Source Models

11 Source Models

Source Models are normally based on a "loss of containment" event. Other types of loss events (such as loss of
product quality or loss of production) are not included here.
Generally a vessel or equipment item within a chemical facility has feeds such as a liquid or inert vapor and outlets
such as vents or liquids. In addition, during a process upset, material may discharge from an emergency pressure relief
device or leak from failed nozzles or piping. Source models are used to estimate discharge rate, total quantity released,
and extent of flash and evaporation for liquids (Figure 11-1).

Relief Release
Relief Release
Vent
Vent
Release
Release
Inert Feed
Inert Feed
Liquid Feed Rate
Rate
Rate Liquid Feed Rate
Liquid Flash and
Liquid Flash and
Aerosol Evaporation
Aerosol Evaporation
Vessel or Droplet Evaporation
Vessel or
Equipment
Equipment Pool
Pool
Rupture Liquid Evaporation
Rupture
Liquid
Evaporation
Release
Release
Containment Dike
Containment Dike
Figure 11-1 Types of source models
The Airborne Quantity for a vapor release is the flow rate calculated at the temperature and pressure conditions of the
equipment when the release occurs. Liquid release requires more complex treatment. As liquid exits equipment or pipe, it
may partially flash or vaporize, there is often small liquid droplets or aerosol which may be carried away with the vapor and
eventually evaporate, and a liquid pool may be formed which slowly evaporates. The Airborne Quantity for a liquid release
is the summation of quantity flashed and quantity evaporated from aerosol droplets and liquid pools.

11.1 Section Objectives

The following objectives are covered in this section:

 Estimation of Vapor Release Rate
o Based on Hole Size
o Based on Vaporization of Liquid
 Estimation of Liquid Release Rate
o Based on Hole Size
o Based on Catastrophic Failure
o Based on Flashing Liquid Flow
o Criteria for Two-Phase Flow

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