3.6 Blasting

Airblast overpressure is the energy transmitted from a blast site, travelling through the atmosphere in the form of pressure waves. As these waves pass a given position, the pressure of the air rises very rapidly, falls more slowly, then returns to the ambient value after a number of oscillations. The pressure wave consists of both audible (noise) and inaudible (concussion) energy. The maximum excess pressure in this wave is known as the ‘peak air overpressure’, generally measured in decibels using the linear frequency weighting.

The airblast levels received at a location remote from a blast are a function of many factors, including:

  • charge mass
  • stemming height and type of stemming
  • burden
  • blast hole spacing, blast initiation sequence and timing delay between holes
  • ratio of the blast hole diameter to the burden
  • face height and orientation of face
  • topographic shielding
  • distance from the blast
  • meteorological conditions.

Models have been developed to assist in predicting the impact of airblast on neighbouring areas. These models are based on empirical data, and normally need to be refined using airblast overpressure measurements taken once the mine is operational.

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