Horizontal barriers are included in international standards as a possible component for the protection of rack storage. A definition of horizontal barrier from the NFPA (National Fire Protection Association) 13, Standard for the Installation of Sprinkler Systems, is “A solid barrier in the horizontal position covering the entire rack, including all flue spaces at certain height increments, to prevent vertical fire spread.” As part of the evaluation of rack storage protection, a simulated fire in a double row rack storage arrangement was used to consider the impact the horizontal barrier had on the fire development. The simulation was done with Version 6.7.1 of Fire Dynamics Simulator (FDS) and Four simulations were run. The temperatures, heat release rates, detector actuation times, and sprinkler actuation times are compared for each scenario. The simulation allowed comparison of results for the particular heat release rate and fire growth specified. The horizontal barrier can be a significant factor in providing protection for rack storage.