I hesitate to use the term 'blast wave' to encompass both the supersonic and the sonic phases due to its potential to mask fundamental differences in the physics at the interface. I refer to Kinney and Graham for this distinction, though similar information can be found in various references.
In the supersonic phase, a thin region exists between the hot, high-pressure gas on the detonation side of the shock and the ambient air through which the shock is travelling, as illustrated in Fig 4-2 below
The interface between a discontinuity in a gas with different state variables is described by the Rankine-Hugoniot condition. This condition is characterised by a set of equations that offer a mathematical model for the process.
The separate sonic phase is characterised by a pressure wave featuring a sharp, almost instantaneous rise in pressure, followed by a smooth reduction back to ambient pressure, as illustrated in Fig 6-3 below:
It also includes a "negative phase"in which the pressure reduces to below ambient pressure.
This shape has been mathematically modelled using the Friedlander equation, and I will refer to it by that name.
As is commonly practised, the depiction of the blast wave often employs a time scale, in contrast to the distance scale used earlier. When both phenomena are graphed on the same set of axes, their distinctions become readily apparent, as illustrated below
While the following table applies to both high explosives such as TNT, C4, and NH4, as well as nuclear explosions, the substantial variation in process intensity may make numerical comparisons somewhat obscure.
Properties | Phase | Phase |
| "Hugoniot" | "Friedlander" |
Propagation speed | Decelerating from hypersonic to sonic. | Steady, Mach 1.0 |
Conditions on blast side the shock | High pressure, hot. | Atmospheric pressure and temperature |
Lifetime, seconds | Very brief:<=10-2 for chemical, <=10 for nuclear | Long: > 102 |
Propagation distance, metres | Very short: <=102 chemical,
<=103 nuclear | Long: > 103 |
Survivable? | No | Yes |
I suggest that the term 'detonation phase' be reserved for the brief, supersonic 'Hugoniot' phase, while 'blast wave' is more appropriately used for the extended sonic 'Friedlander phase' due to these distinctions.