R. Meyer J. Köhler A. Homburg Explosives

Permissibles; Permitted Explosives
Higher safety grades are achieved in ionexchange explosives in which
the ammonium and sodium (or potassium) ions are exchanged; instead
of
NH4NO3+(inert) NaCl = N2+2 H2O+1/2O2+(inert) NaCl
the reaction is:
NH4Cl+NaNO3 (or KNO3) = N2+2 H2O+1/2O2+NaCl (or kcl).
Thus, a flame-extinguishing smoke of very fine salt particles is produced
by the decomposition reaction itself. Combinations of salt-pair
reactions and “classic” detonation reactions quenched by adding salt
are possible.
Permitted explosives with a higher grade of safety are powder explosives.
They contain a minimum percentage of nitroglycerine-nitroglycol
to ensure reliable initiation and transmission of detonation
and to exclude slow deflagration reactions. The mechanism of salt-pair
detonation in confined and unconfined conditions is explained in W Detonation,
Selective Detonation.
2. Testing galleries
Versuchsstrecken, Sprengstoffprüfstrecken; galeries d’essai.
All coal-mining countries have issued detailed regulations for the
testing, approval, and use of explosives which are safe in firedamp.
The main instrument for these tests is the testing gallery.
Fig. 18. Testing gallery with borehole cannon.
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A test gallery consists of a steel cylinder which initates an underground
roadway; the cross sectional area is about 2 m 2 (5ft P; one end
is closed by a shield of about 30 cm (1ft) P, against which the cannon
is placed. The other end of the chamber which has a volume of ca.
10 m 3 (18ft length) is closed by means of a paper screen. The
remaining part of the tube length (10 m; 32ft) behind the paper screen
is left open to the atmosphere. (The gallery tube can be constructed in
closed form if the noise of the test shots can be diminished.) After
charging and positioning the cannon, the closed chamber is filled with