Upward flame spread over discrete fuels has been analyzed through experimental research on vertical arrays of alternating lengths of PMMA and insulation. By manipulating the lengths of the PMMA fuel and the insulation, several important trends related to flame spread were identified and assessed.

The peak flame spread rate for arrays with 4 cm lengths of PMMA occurred at a fuel percentage of 67%; for arrays with 8 cm PMMA, a peak flame spread rate occurred at fuel percentages of 67%, 80%, and 89%. It has been hypothesized that increased air entrainment at these fuel percentages maximizes the flame spread rate.

Based on observed trends, this study proposed a method for approximation of the fuel spread rate at various fuel percentages. Given reasonable estimates for the homogeneous flame spread rate and the lowest fuel percentage that sustains spread, an estimation for intermediate spread rate values is feasible.