Detonators:
a guide to the blasting cap
Aluminum & Copper Shell
Electric Detonators and
Nonel Shock Detonator
Detonators, sometimes referred to as blasting caps, are the “spark plug” or primary shock
input for many types of industrial and military explosives and improvised explosive
devices. Bruce Koffler explains their importance, construction and key characteristics.
etonators are used to initiate and powerful primary high explosive. The solid copper, with plastic insulation. For
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the release of stored safety fuse acts as a time delay, burning at special applications, the wires may be
explosive energy contained in the rate of approximately 45 seconds per made of iron or steel.
dynamite, certain “cap- foot (30cm), allowing the blasting operator Another type is the Nonel shock tube
sensitive” water gel and to exit from the area after lighting the fuse. detonator. A single hollow plastic tube and
slurry explosive cartridges, Electric detonator types designed to be sealing plug are crimped into the open
detonating cord, sheet explosives, flexible triggered electrically for more precise mouth of the detonator shell. The entire
linear tape explosives, cast boosters, and blasting, have a bridge-wire and match length of the tube’s interior channel is
binary explosives. assembly configured into a rubber or lightly dusted on the inside with a
In their most common configuration, they plastic plug. This is inserted into the open molecules-thick layer of explosive powder.
consist of a small diameter (4.5mm-7mm) end of the shell and the shell is factory- An initiating spark or flame, input at the
deep-drawn metal shell. The shell is a cup or crimped around it to lock it in place and other end of the shock tube, triggers the
tube, closed at one end and open at the other. seal out moisture. There are two leg-wires explosive dust to very rapidly transfer
Common lengths are between 30mm and or lead wires that pass through the plug energy down the length of the tube. When
70mm, yet shorter and much greater length and terminate in the bridge-wire, usually a this energy reaches the flash and main
special-purpose detonators are also available. very fine platinum wire filament, smaller in charges in the shell, the detonator
The “plain” types are actually half empty. diameter than a human hair. Sensitive explodes. Energy is transferred down the
They are designed for the insertion of a match material surrounds the bridge-wire, tube at the rate of about 2,000 metres per
safety fuse (time fuse) into the void, then which is in contact with the internal flash second. The shock tube is visible to X-ray
usually field-crimped in place, by the charge that in turn initiates the main as an organic material.
blasting operator. The lower portion “base” charge. There may also be a delay These different types of detonators each
contains a flash charge and the main element (measured in milliseconds), in the have their own individual X-ray signatures,
charge (or base charge) of very sensitive explosive train. The two wires are usually and being very small and thin-walled, can
Aviationsecurityinternational February 2009 www.asi-mag.com 15
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