Foam spread over a liquid pool

Firefighting foam is widely used to extinguish liquid pool fires. To model the extinguishment of pool fires, the spread of the foam over the fuel surface needs to be predicted. Equations of motion for predicting the spreading of foam over a confined liquid pool have been developed. These equations are a variation of the shallow water equations, which assume height-averaged dependent variables and hydrostatic pressure. The derivation includes source terms in the mass and momentum equations that account for mass losses and gains as well as a variety of external forces acting upon the foam. Foam is a non-Newtonian fluid that requires special consideration when determining shearing terms in the momentum equation. Constitutive models were developed to predict the shearing between the foam and fuel. Results from these models indicated that the rate of foam spread over fuel can be increased by reducing the foam yield stress and viscosity. Reductions in foam viscosity had the largest impact.