Use of aqueous foam to reduce blast noise

Various laboratories have investigated the use of aqueous foam to reduce blast overpressures. In 1976, the Royal Armament Research and Development Establishment of the United Kingdom measured the reduction in environmental noise produced by filling bomb chambers with high‐expansion fire fighting foam. Reductions in the A‐weighted peak levels were measured as high as 20 dB. However, these results cannot be applied to other configurations because of the confinement of the explosives and the indirect propagation path from explosives to microphone. This paper describes a study conducted by the US Army Construction Engineering Research Laboratory (CERL) which measured the reduction in (1) C‐weighted and flat‐weighted sound exposure level and (2) the flat‐weighted peak level produced by covering explosive charges with high‐expansion foam. CERL used charges ranging in size from 0.135 to 5 lb (0.06 to 2.3 kg): foam depths varied from 6 in. to 4 ft. 9 in. (0.15 to 1.4 m). All of these data, with the exception of the 0.135‐lb (0.06‐kg) data, display a linear relationship between reduction in levels and cube‐root scaled foam depth. The 0.135‐lb data are also linear within experimental accuracy, but display less reduction with scaled foam dimensions.