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Suppression system by water spray such as sprinkler system is installed in many buildings and well-known as one of highly effective fire protection methods for enclosure. On the other hand, sprinkler system (hereinafter referred to as SP) would have other effects, such as cooling effect in a compartment, cooling effect of building structure and attenuation of radiant heat flux from fire. In this paper, attenuation of radiant heat flux through water droplets were investigated by full-scale experiments. The fuels were used n- heptane and ethanol for comparison of influence of soot particle. 5 kinds of sprinkler nozzles were used in the experiment. Firstly, the fundamental data of the nozzles and flame such as droplets diameter, droplets velocity and distribution of water droplets and radiant spectrum of flame were investigated. Moreover, absorption and transmittance of radiant heat flux was calculated by the Mie theory. And also, an improved prediction model on radiant spectrum was used to predict the radiant spectrum of flame. Thus, absorption and transmittance of radiant heat flux can be calculated by above flame data and fundamental SP data. As the result of calculation parametrically, radiant heat attenuation increases with decreases of droplets diameter. And, it increase approximately linearly depends on amount of total droplets.