R. Meyer J. Köhler A. Homburg Explosives

41 Brisance
Bridgewire Detonator
Brückenzünder; amorce à pont
Bridgewire detonators are used in industrial blasting operations for the
initiation of explosive charges. They contain an incandescent bridge
made of thin resistance wire, which is made to glow by application of
an electric pulse. An igniting pill is built around the wire by repeated
immersion in a solution of a pyrotechnical material followed by drying.
The igniting flash acts directly onto the detonating surface in the case
of instantaneous detonators; in delayed-action detonators it is sent
over a delay device onto the detonating surface of a blasting cap
which has been pressed onto the detonating pill so as to produce a
water-tight bond with it. Non-armed bridgewire detonators have an
open casing, into which a blasting cap may be inserted.
The “U”-detonators which are now employed in mining in the Germany
need a pulse of 16 mW·s/ohm; the earlier detonators required only
3 mW·s/ohm. Thus new detonators afford much better protection
against stray currents. Locations exposed to electrostatic stray
charges (thunderstorms) and which are therefore particularly dangerous,
are equipped with low-sensitivity detonators, which require as
much as 2500 mW·s/ohm for actuation and may therefore be considered
safe (“HU”-detonators).
The delayed-action detonators may be set for a delay of half a second
(half-second detonators) or for a delay of 2–34 ms (millisecond detonators).
Blasting with the latter type of detonators results in a larger
yield of blasted stone fragments; moreover, a smaller shock will be
imparted to the ground around the explosion site.
In coal mining only copper casings rather than the conventional aluminum
casings are permitted because of the danger of firedamp. Explosive
charges equipped with bridgewire detonators are fired by wireconnected
W Blasting Machines from a safe location. If several
charges have to be initiated at the same time, the detonators are
connected in series with the connecting wire. Parallel connection of
the detonators is used only in special cases (extremely wet conditions
with danger of shunting); special blasting machines must be employed
for this purpose.
Brisance
Brisanz
The performance of an explosive cannot be expressed by means of a
single characteristic parameter. Brisance is the destructive fragmentation
effect of a charge on its immediate vicinity. The relevant parameters
are the detonation rate and the loading density (compactness) of