An investigation of the efficiency of water sprays in the protection of buildings and fire-fighting personnel from heat radiation has resulted in a general theoretical study of the transmission of radiation through a layer of water spray of large drops. The treatment is based upon the work of Theissing⁽¹⁾ and takes account of multiple refractive scattering in dense sprays and extends the method to absorbing sprays.

The problem of the single drop is approached from the point of view of geometric optics, from which approximate expressions are derived for the absorption of a drop in terms of the absorption index for any given wavelength and for the angular distribution of radiation transmitted by a single drop. Since the absorption of thermal radiation depends markedly on the drop size it is found that the transmission of such radiation departs from the simple exponential extinction law when the drops and the quantities of water in the sprays are small. When the drops are less than about 0.005 cm in diameter, back reflexion by the spray may become significant.