Fire Spread in Liquefied Petroleum Gas Cylinder Stores

The storage of large numbers of Liquefied Petroleum Gas cylinders at filling plants and distribution depots is necessary to quickly restock retail outlets. In the event of a fire, this may present a considerable hazard to fire service personnel and to the surrounding community.
The majority of LPG cylinders are fitted with pressure relief valves in order to prevent explosion when exposed to fire. Incidents where large numbers of cylinders have been involved in fires have demonstrated that although the prvs do not always prevent explosions, they markedly reduce their severity.
A consequence of fitting prvs to cylinders is that fire spreads rapidly through stacks of cylinders due to the action of the flares from the relief valves on other cylinders in the stack. This study examines the mechanism of fire spread and models the processes involved by the use of computer simulations.
Three computer models were written:
The Single Cylinder Model examines the thermo-hydraulic behaviour of a single LPG cylinder when exposed to fire including the pressure within the cylinder and the temperatures of the cylinder and its contents. A comprehensive set of heat transfer paths into, through and within the cylinder are modelled together with bulk boiling of the liquid contents, venting of the material through the prv and failure of the cylinder. The model predictions have been found to be in good agreement with experimental data.
The Simple Stack Model uses a graphic display to illustrate the fire spread based on a simple heat transfer model approximated from experimental data.
The Rigorous Stack Model combines the previous models with a procedure for the calculation of radiative/convective heat transfer from a prv flare to cylinders in a stack, which included an _ empirical correlation for the combined emissivity/configuration factor. This correlation was developed from the results of an experimental programme, which involved measuring the heat input to water filled cylinders from a simulated prv flare. The fire spread was again illustrated by the use of a graphic display.
The discharge coefficient for a typical pressure relief valve was determined experimentally and was used in the Rigorous Stack Model and the Single Cylinder Model to calculate the LPG release rate.
The Rigorous Stack Model was used to simulate earlier experimental trials. Some values of the input parameters could not be sufficiently well defined from the results of these trials, but reasonable agreement was obtained between the small scale experiments and the simulation.