In recent years there has been considerable interest in the growth of fires and the subsequent movement of smoke and toxic gases in multicompartment structures. This activity is motivated by the need to understand and predict the environmental conditions which occur as a fire develops and spreads. Much of the attention has focused on the development of numerical models which are able to make reasonably accurate predictions from the onset of ignition. Most of the effort has centered on the control volume or zone model approach. While this approach loses some of the detailed analysis available from a fully differential model, such as the velocity profile in a vent, much is gained by the reduction in the number of equations to be solved for each compartment.

As with other types of models, the basic equations to be solved include conservation of mass and energy. These equations are usually recast into predictive equations for temperature, pressure, and volume (layer thickness). An almost universal approximation is that the transient pressure term (dP/dt) is not a significant process in energy transfer. One reason for this approximation is the assumption that an algebraic equation is easier and faster to solve than a differential equation.

We have rederived the zone model equations for the usual two-layer model, retaining the transient pressure term. This allows us to recast the equations in a simpler form which is symmetric for the “upper” and “lower” layers.

We have found this form of the equations to be computationally faster. Also, the transient nature of the equations can be seen in the stability of these equations as well as in the stability of physical processes such as flame puffing and flashover.

We have constructed a multicompartment model using a framework discussed in the paper. Testing this model has been done using experimental results discussed in the paper. These comparisons, plus current calculations and timings for the various models, are presented.