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~ v~B~TE~N sounds they generate (rustling of windo++a, dishes. etc. I Oficn. thev will believe they have felt ground movement when it was only the structure responding to the airhlast. Uli( :9l'e~J.~f1/t r)I'Ii111'ltl.;ti~l `Itl In a homogeneous atmosphere, air overpressure will attenuate in a known ntanner. I lo+vcvcr, a homogeneous atmosphere is nut the normal conduian Weather conditions are continuously changing, which m turn alTrct the air overpressure. Other factors, which will atl'ect air overpressure, are permanent such as topography Sound pressure levels may be enhanced or reduced by topographic relicf.:1n example of this would be a shadow rone. A shadow lone +vould he behind a hill or txyund the lip of the pit, wore as the obsc;rvcr is protoctcd from the activities dc,~ep within the pit. fiowceer, a location farther away. positioned on a hillside rising atxwo tho pit, rnuld he more exposed to the air overpressure, so that the air overpressure levels may bo higher farther away. Likewise, if an air overpressure is generated between steep +calk of a valley or cam•on. the airhlast will decay quickh due to reflecting olt' the walls, unlike those generated on an open plain which will decay more slowh. I~or each doubling of distance, ground vibrations typically decay to I~_ their former value, which is eyuivalont to a slopo of-1.6. Air overpressures do not decay as quickly as ground vibrations. Because there arc so many variables, which dcternuno the decay of uir overpressures, there arc numerous studies with diffemnt conclusions. Flow•evcr, there is usually a general agreement in concept The majority of the data slum blasting activity is in the runge of 6 d13 per doubling of distance {-LO slope) to 7 2 dB Ixr doubling of distance (-1.2 slope). .A slope of -1.0 means that the pressure is proportional to distance, decaying to ' : the ti~rnter pressures when the distance is doubled. hoe overall purposes applied to blasting operations a decay slope of -I.I or 6.G d[3 per douhhng of distance is used, as socn in figure 3 I'mm I ~°i liiiiilm 191•F, aLuler's F4Mt+ank m r is In \ of ~.~ ~ ~ t i ~~ ~ w ~4 \4',o i,,,.,, i ~~ *,~ • ~ g owl w ~~d \~~. ~ ~. \~i ~ Nate Al -1)W ~• ~\ ~' ~ ~~ i n on um ` tins, ~~ Figure 3 Cube Rivet Scaled Distance (Nlbv''rl O+rrpressurc versus Charge Burial In the graph, the distance is scaled Inonnalircdl by the cube root ol'the maximum charge +celght per delay, rather than the square root By cube rooting the maximum charge weight per delay, it usually gives less scatter, although this is not unanimously true 1 11