The gas energy released during the detonation process causes the majority of rock breakage in rock blasting with charges confined in boreholes. The gas pressure, often called explosion pressure, is the pressure that is exerted on the borehole walls by the expanding gases after the chemical reaction has been completed.
Explosion pressure results from the amount of gases liberated per unit weight of explosive and the amount of heat liberated during the reaction. The higher the temperature produced, the higher the gas pressure.
If more gas volume is liberated at the same temperature, the pressure will also increase. For a quick approximation, it is often assumed that explosion pressure is approximately one-half of the detonation pressure.
It should be pointed out that this is only an approximation, and conditions can exist where the explosion pressure exceeds the detonation pressure. This explains the success of ANFO which yields a relatively low detonation pressure, but relatively high explosion pressure.
Explosion pressures are calculated from computer codes or measured using underwater tests. Explosion pressures can also be measured directly in boreholes, however, few of the explosive manufacturers use the new technique in rating their explosives. A review of some very basic explosives chemistry helps one to understand how powdered metals and other substances effect explosion pressures.
Reference
Department of Transportation, «Rock Blasting and Overbreak control. »
