Air blast or air over pressure is one of the negative effects of blasting. An air overpressure (air blast) is an atmospheric pressure wave emanating from the explosion in air. This wave comprises: • The audible part of the airblast (acoustic): higher frequency (from 20 to 20,000Hz); and • The sub-audible part of the airblast (infrasound): low frequency (below 20Hz). Unlike the audible air overpressure (acoustic), which is classified as noise, the air overpressure at frequencies below 20Hz is cal