A History of Research and a Review of Recent Developments

The development of low and high explosives 5
lower and the duration of the impulse much greater. Detonation, as opposed to
deflagration, is obtained by the use of a burster charge containing a mass of
conventional high explosive about one-hundredth of the FAE mass. The control
of FAE weapons was thought to be uneven, and research in the USA was reduced
in the 1970s, but more recently the Soviet air force used weapons of this type in
Afghanistan, and there are reports in the technical military press of the very
successful use of FAE bombs by the US forces in the Gulf War.
Let us now turn to the detonation process, which has been considerably
developed during the past century. There are now many methods for the safe
detonation of high explosives, and nearly all consist of the initiation of a
shock wave into a base charge which then detonates the main explosive charge.
Most recruits to the armed services in the first half of this century will have
handled the small aluminium tubes containing a priming charge of mercury
fulminate (HgC 2N 2O 2), or lead azide (PbN 6) and a secondary charge of PETN.
The primary charge could be set off by impact, as in the spring released system
of a hand grenade, or via a length of safety fuse capable of initiation by a
safety match.
The priming charge can also be ignited by electrical means, and electrical
shotfiring is now widely used. When an electrical charge is connected to the
detonator it heats up a fine wire which then ignites a flashing compound. This
‘fusehead’ fires the primer and base charges. Delaying elements can be
introduced between the fusehead and the primary charge, or the fusehead can
be set to explode so quickly that the entry of the firing current and the detonation
of the base charge is virtually instantaneous. The use of electrical detonation
must be carefully controlled in very sensitive environments where there is a
risk of premature firing by static electricity, or where there are dangerous
methane or dust clouds. Special detonators have been developed to overcome
these problems and to avoid accidental pre-detonation. These are described
in handbooks and in the marketing literature of manufacturers such as ICI
Nobel and Dupont.
The other main detonating medium is the ‘detonating cord’ and ‘Cordtex’
is a universally used version in blasting and quarrying operations, explosive
cutting, and underwater operations. A core of PETN is surrounded by tape
and wrapped with textile or synthetic yarn, and this cord is completely enclosed
by a white plastic tube. It has a high velocity of detonation which means that
it will initiate most commercial explosives, and it can be initiated itself by
most of the standard detonators. There is plenty of information on methods
of using Cordtex for various blasting operations, involving detonating relays,
jointing and branching methods, and initiating systems.
A major area of development has been the artillery fuse. These were originally
the powder train fuses, or rather inaccurate mechanical devices, but more
recently the need for high firing rates has led to the evolution of the electronic
time fuse and to the electronic fuse with a high-explosive boosting charge.
The fuse is the shaped end of a mortar or artillery projectile and consists of an