R. Meyer J. Köhler A. Homburg Explosives

245 Permissibles; Permitted Explosives
charge (containing, e.g., mercury fulminate with chlorates or lead
trinitroresorcinate with Tetrazene) is ignited by the mechanical action
of a firing pin.
Percussion Primer = Percussion-actuated initiator.
Perforation of Oil Wells
Perforation von Erdölbohrlöchern; perforation des trous de sondage
In petroleum technology, shaped charges fired from special firing
mechanisms (jet perforators) are lowered into the borehole down to
the level of the oil horizon. Their purpose is to perforate the pipework
and the cement work at the bottom of the borehole, so as to enable the
oil to enter it.
Permissibles; Permitted Explosives
Wettersprengstoffe; explosifs antigrisouteux
1. Definition
Shotfiring in coal mines constitutes a risk in the presence of firedamp
and coal dust. Permitted explosives are special compositions which
produce short-lived detonation flames and do not ignite methane-air or
coal-dust-air mixtures.
The methane oxidation
CH4 +2O2 = CO2 +2 H2O
needs an “induction period”*) before the reaction proceeds. If the time
required for ignition by the detonation flames is shorter than the
induction period, then ignition of firedamp will not occur. Thus, the
composition of permitted explosives must ensure that any secondary
reactions with a rather long duration, which follow the primary reaction
in the detonation front, are suppressed and that slow W Deflagration
reactions are avoided (W Audibert Tube).
Such explosives are known as “permissibles” in the USA, as “permitted
explosives” in the United Kingdom, as “Wettersprengstoffe” in
Germany, as “explosifs antigrisouteux” in France, and as “explosifs
S.G.P.” (sécurité grisou poussières) in Belgium.
Safety measures to avoid ignition of firedamp uses salt (NaCl) which is
included in the usual compositions of commercial explosives. It lowers
the W Explosion Temperature and shortens the detonation flame.
* Contrary to the delayed ignition, the oxidation of hydrogen with the salt-pair aid
of an ignition source, 2 H2 +O2 = 2 H2O, is instantaneous.