Alaskan black spruce often exhibits extreme fire behavior that threatens human values. Theoretical crown fire potential at three recently constructed fuel break treatments were assessed to reducing such risks. Available canopy fuels were reduced by 13% to 75% in thinned and pruned units compared to controls. Scenarios were developed under hot, dry windy weather and average summer day conditions using the Nexus 2.0 fire behavior modeling program. Projected fireline intensities and flame lengths were little changed in two of three treated units, while headfire rates of spread were almost doubled in the treatments relative to the control under certain conditions. Simulations indicated fuel modifications did not preclude crown fire activity, but did reduce the crown fraction burned, indicating a lower potential for spotting. The threshold for sustained active crown fire development was substantially higher in the open treated stands compared to the denser control stands. Fuels modifications effectiveness in altering fire behavior was a trade-off under both weather scenarios.