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I, VIBRATECH® causes the sound waves to refract upwards, thus limiting the distance to which sounds can be heard. If the opposite conditions aze occurring, where the air is warmer above the surface, this is called temperature inversion. In this case the sound waves will be curved back downwazd toward the surface allowing the sounds to be heard at greater distances. 2) Wind Propagating air overpressures are bent by wind. When propagating downwind the waves are bent downward and when propagating upwind the waves are bent upward. Therefore, downwind air overpressures diminish slower than upwind air overpressures. This effect can account for a difference of 10-20 dB with a 20 mph wind or from no wind. Mild crosswinds have little or no effect; however, turbulent winds may mask the sound as well as disrupt the continuity of the air overpressures. On occasion there is a phenomenon where there are layers in the atmosphere. These layers could be either temperature or wind layers where the winds are moving in opposite directions. These layers may cause reflections of the sound waves. Depending on the temperature gradients, there may be a relatively quiet zone at intermediate distances, and then at greater distances the sounds could increase. Atmospheric layers are similar to that of sounds being reflected off a smooth lake. • Time of Day The time and day of blasting is a very important part of the blasting operation. It is important to have knowledge of the community around the blasting operation and what aze the more favorable times to blast. • Topography Topography may have a positive or negative affect of the air overpressures produced by the blasting operation. Some of the positive affects maybe hills, large stockpiles, or the shape of the pit, which could block or deflect the air overpressures. While the negatives affects could be from ' reflections from a high back wall or from a narrow canyon wall. It should be noted however that any one of these could be positive or negative depending on where the complaints are coming from in relation to the blasting activity.