Abstract
Blast hole pressure is the starting point for many blast design calculations, but the way in which it is usually derived, from measured detonation velocity, indicates that more thought is needed as to its true meaning and implication. The general impression is given that the energy in the hole is defined by velocity of detonation (VoD), but this is rarely the case. VoD is defined by the energy released in the detonation driving zone between the shock front and the sonic (or CJ) surface, and for commercial explosives it is normal for reaction not to be complete within this zone. Reaction and energy delivery continues behind it, not reflected by VoD. Thus it would be more appropriate to use the theoretical VoD, not the measured VoD, to derive the starting pressure, since this would reflect the energy input of full reaction. In decoupled situations, the derivation of pressure at the blast hole wall using a polynomial decay concept is also of debatable value, and an alternative is offered.
Acknowledgements
African Explosives Limited gave permission to publish this paper, and sponsored significant interaction with technical authorities in detonation over the years. I am particularly indebted to Dr Martin Braithwaite, Dr Ian Parker and Dr Finn Ouchterlony for patient discussions on the topic.