Quintiere and Harkleroad found that their data from the Lateral Ignition and Flame spread Test (LIFT) could be correlated based on a simplification of the thermally thick solution. The simplification was the empirical determination of the quantity F(t) as shown below:
Where:
| h | = | overall heat transfer coefficient accounting for both radiation and convection |
Although an exact expression for F(t) is available for a linear approximation of thermally thick solids with constant properties,26, 27 it was determined empirically due to the limits of the thermally thick solution and the predominant form of their results. The empirical values for F(t) are:
Where:
| b | = | a constant related to k ? c |
| t m | = | the characteristic time indicative of the time to reach thermal equilibrium, since F(t) = 1 at t = t m |
Figure 4 shows the Radiata Pine data plotted as 
versus 
showing the linear relationship found by Quintiere et al. The (x) symbols indicate the data points and the solid line is the best-fit linear regression line. The slope of the best-fit line is b, and t m is the time to thermal equilibrium, i.e., the intercept with 
. When the data are plotted in this form, the regression line must pass through the origin. A certain amount of judgment is also required on the part of the researchers. In this particular case, the data above 
were ignored in order to obtain...
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