Spray application is a method commonly used to protect structural steel columns from direct fire exposure. The endurance time for a column during a fire test is the time at which temperature at any level exceeds 1000 F. In this study a one-dimensional analysis of heat conduction was performed to define the pertinent parameters. For a fire resistive material this parameter was of the form (A/D)h, where A is the cross-sectional area, D is the heated perimeter; and h is the thickness of fire resistive coating. Correlation of fire test data with the parameter (A/D)h showed that endurance point time for a range of wide flange columns could not be described with a single equation. When (A/D) ratios for the larger columns were determined on the basis of the web dimensions, a single linear relationship between (A/D)h and the endurance time for the complete size range of columns was obtainable. Data from tubular and pipe columns also correlated linearly with the (A/D)h parameter.