This work deals with the mathematical modelling of the response of tanks containing pressure liquefied gases when subjected to accidental fire conditions. The developed model consists of a fire model, a wall conduction model and a free convective model for the liquid and vapour spaces.

The fire model considers both radiation and convection heat transfer from the flames to the tank wall. The flames are assumed to occupy a rectangle surrounding the cylindrical tank. The walls of this rectangle are represented as black surfaces, while the fire is assumed to have a uniform temperature and absorption coefficient. The surface-to-surface exchange factors are computed numerically and used in the radiation balance equations which are solved to give the radiation heat flux at the tank wall as a function of circumferential location. Convection heat transfer from the flames to the tank wall is calculated using a heat transfer coefficient obtained from experimental heat transfer measurements for forced convection to cylinders in cross flow. The convective and radiative heat fluxes are combined to give the total heat flux applied at the tank surface. The developed fire model is used to obtain results for different fire conditions, which are presented and analyzed.

The heat transfer through the tank wall and the free convective flows in the tank contents are governed by the conservation laws of mass, momentum and energy. The conservation equations are solved numerically using a semi-implicit consistent formulation and a boundary fitted coordinate system. The accuracy and efficiency of the developed model is extensively evaluated using transient and steady state problems for which experimental data or numerical benchmark solutions are available in the literature.

Radiation heat transfer from the vapour-wetted-wall to the vapour and liquid/vapour interface is determined using the net radiation method for an enclosure filled with an isothermal gas. Heat transfer by radiation to the interface is found to enhance the interface temperature and hence the rate of pressure rise.

The developed model is employed to study the behaviour of LPG tanks to fire exposure. Comparisons of predicted results with experimental data indicate that the model can accurately predict the tank behaviour to these conditions. The effect of filling level, tank size, fire temperature and fire exposure on the tank response is investigated and the major conclusions are presented.