EFFECT MODELS FOR CONSEQUENCE ANALYSIS

"Every cause must produce an effect and every effect must have a cause " (Law of Universal Causation in Logic)

We discussed in Chapter 5 that there are two components to consequence modelling-effects models and vulnerability models. This chapter deals with the physical effects of releases of hazardous materials and the subsequent events that generate thermal radiation, toxic gas concentrations or explosion overpressures. Vulnerability of receptors is dealt with in Chapter 7. Wells (1980) has described a number of issues of how to incorporate the effects and vulnerability modelling in process plant design.

It is not the purpose of this chapter to give a complete coverage of effect models. The chapter provides an overview of the key issues and approaches, providing references for more detailed modelling information. What is given are insights and suggestions for the use of such models in hazard analysis. A number of well established software tools are available for these predictions.

Factors Affecting Release Modelling
The first category of events is the release of a hazardous material from containment such as a pipe, tank and vessel or transport tanker. Table 6-1 gives a summary of the types and location of releases (Lees, 2001) which could be encountered. Each release has a specific characteristic which is dependent on
(i) the physical state of the material (solid, liquid, gas)
(ii) the physical situation (pipe, pump, vessel)
(iii) physico-chemical properties (density, viscosity, vapour pressure,
reactivity)
(iv) operating conditions (pressure, temperature, concentration)