Human perception is not a good measure of blast effects. Blasting and other vibration producing activities do not take place in the same location each time. The change in distance may affect the actual vibration levels and this would be supported by seismograph measurements. Whether or not the person is expecting the blast or whether they are inside or outside at the time of the blast may affect perception as well. In the case of construction blasting the actual blasts may change the explosives type or amount necessary to break rock being excavated. In addition, the size of the blast, orientation and direction of initiation may also affect perception. Also, the airblast may cause an additional effect. The ground vibration travels faster than the airblast (noise) associated with the detonation, and each affect the structure differently. As airblast is highly affected by environmental conditions, mainly wind, the effects change with each blast.