Airblast (overpressure) is a low frequency, sub-audible fluctuation of air pressure that radiates from blast sites through the atmosphere at the speed of sound (340 m/s) and reduces at an approximate rate of 9 decibels with doubling of distance. The velocity of airblast is lower than seismic waves (2,200-750 m/s) and therefore the airblast period occurs after immediate the ground vibration waves arrive.

The duration of airblast is that of a blast’s initiation period, typically less than 1 second for most quarry blasts. Depending on distance from the blast site, the number of blast holes and initiation sequence used, the combined effects of ground vibration and airblast may be perceptible for 2-5 seconds.

While airblast is sub-audible, it can be perceived by people inside buildings due to structural and audible responses such as a rattling sliding door, a creak of roofing materials or a wobbling window pane. At perceptible levels the effects can be likened to a sudden, short-lived wind gust though the effects are difficult to distinguish from ground vibration responses. The threshold of airblast perception for people inside buildings is considered 100-105 dBL.