R. Meyer J. Köhler A. Homburg Explosives

Detonation
Fig. 12. The Hugoniot curve and the Rayleigh line in the p–v diagram.
3. Selective Detonation
Selectivity in the course of a detonation process, as described by
Ahrens, is noted when processes with very different sensitivities, and
thus also with very different induction periods, participate in the intensive
chemical reaction (W 2. Detonation Wave Theory) produced by
the shock wave. If the intensity of the shock wave is very low owing to
external conditions – explosion in an unconfined space, for example –
the induction periods of less sensitive reactions may become infinite,
i. e., the reaction may fail to take place.
This selectivity is important for ion-exchanged W Permitted Explosives.
The proportion of the nitroglycerine-nitroglycol mixture in these types
of permitted explosives is chosen so that it would just produce a
detonation as if it were dispersed in an inert salt bed. The decomposition
reaction of the ion exchanged salt pairs NaNO3 (or KNO3) + NH4Cl
NaCl (or KCI) + N2 + 2 H2O + 1/2 O2 is insensitive and only takes place
if the detonation process is favored by confinement; otherwise, the
mixture will behave as an inert salt. Thus, if the explosive is detonated
while unconfined (e.g. in angle-shot mortar test or because the confinement
was destroyed in the previous blast), the only reaction which
takes place is that of the nitroglycerine-nitroglycol mixture which is fast
and is limited by its relative proportion and is thus firedamp safe. If the
explosive is detonated in an undamaged borehole, double decomposition
will take place, and the explosive can develop its full strength.
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