Fires may follow from any hydrocarbon release given exposure to the ignition sources present at the facilities in question, and can result in fire loads beyond the design limits of the facilities. Fire analysis is therefore in many cases a significant part of a QRA.
The main objective of the fire analysis is to provide a sound basis for setting design fire loads such that the risk for personnel, assets or environment is within acceptable limits. Further, fire analysis is used for evaluating impairment of escape ways (smoke/radiation), and evaluating how the actual layout affects the consequences of fires. The aim is to provide useful advice on escape/layout design or to describe the fire risk for an existing plant.
Fires may be modelled using analytical/empirical models describing the shape radiation, smoke, effect of wind, and so on. Such models are used in Lilleaker’s risk analysis tool ASAP, as described under QRA.
Sometimes significantly more accurate modelling of fires is required, and in such cases we apply the CFD tool KFX (Kameleon FireEx). Here, fires can be modelled in 3D, taking into account all relevant aspects affecting the fire, and results for heat radiation, temperature, smoke etc. can be measured and plotted as required.
In some cases, a full probabilistic fire analysis may be required. An overview of the main stages in probabilistic fire analysis is as follows, using the CFD tool KFX and the risk analysis tool ASAP:
Fire frequencies and durations are calculated in ASAP which provides transient calculations of the leaks, gas dispersion, detection and ignition. The CFD tool KFX is applied for incident heat/temperature calculations on targets of interest. Combining the results of these two programs gives the fire exceedance frequency on each target.
Example of a fire simulation plot, illustrating heat and smoke: