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An intentionally set fire in a warehouse containing high rack storage resulted in total destruction of the structure and contents. The warehouse was protected by a sprinkler system designed for commodities stacked to heights substantially less than was resident at the site at the time of the fire. Consequently, enhanced fm growth and heat transfer, coupled with inadequate water spray distribution caused by the excessive storage heights, resulted in uncontrollable fire spread, and subsequent total destruction of the site. To evaluate and demonstrate the capability of the in-place sprinkler system to protect the structure and contents for the mandate storage height, a study was conducted to compare heat transfer conditions in the area above the racks for the design storage height, and for the actual storage height reported prior to the fm. The study involved experimental determination of fire growth and mass loss rate dynamics for parallel panels of heavy grade cardboard, simulating stacked boxes. The data was correlated in terms of formulas derived from theoretical analyses of upward flame spread and vertical mass burning, and the results used to predict upward flame spread rate, flame height and plume temperature rise in the rack fire. The thermal environment in the ceiling area above the racks, and the effect of sprinkler spray on the temperature reached by the ceiling/floor assembly, was then estimated for the two storage heights. The calculations were finally used to determine the ceiling structure endurance. To visualize the results of the study, a computer generated animation of the progress of the fire was also developed. For the design storage height, the results of the study show that the existing sprinkler system would have prevented structurally destructive thermal conditions in the ceiling, and would probably contained the fire in racks to near the area of origin.