AristaTek recently received an E-mail
asking why the explosive Semtex was not in the PEAC
database, although the explosive C-4 was in the PEAC
database. Semtex is the plastic explosive probably most
widely used by international terrorists.
Semtex is a plastic bonded explosive
manufactured by Explosia, a company in the Czech
Republic. It was invented in 1966 by Stanislav Brebera
for the Czechlovakian government, which then sold the
explosive to North Vietnam as a counterpart to the
U.S.-made C-4 plastic bonded explosive. After the
collapse of the Soviet Union, Semtex could be purchased
on the open market. Semtex has many industrial uses, but
unfortunately is also a favorite of terrorists. Only
recently has the Czech government imposed controls.
Both Semtex and C-4 contain two
powerful explosives RDX and PETN [also known as
cyclonite and pentaerythritol tetranitrate] but differ
in the plastic binder material. The explosives RDX and
PETN are manufactured worldwide. Plastic bonded
explosives containing RDX and PETN and binders are
manufactured in several other countries, and theft is
possible resulting in the explosive following into the
hands of terrorists. Iran is believed to manufacture
plastic bonded explosives. By agreement, several
countries that manufacture plastic bonded explosives
(U.S., Canada, Austria) incorporate tracer materials to
enable the explosive to be traced to the country of
In this month’s article, we will
review explosives that might be used by terrorists. This
is a continuation of a PEAC Newsletter article which
appeared in December 2003 [available at /Newsletter/03%2012%20December/Technically%20Speaking.htm
Classification of Explosives
Explosives can be classified into two
broad categories, called “high order explosives” or “low
order explosives”. High explosives produce a defining
supersonic over-pressurization shock wave. Detonation
rates are usually between 1000 to 10000 yards/second.
Examples are TNT [trinitrotoluene], PETN
[pentaerythritol tetranitrate], RDX [cyclonite],
plastic-bonded explosives such as C-4 or Semtex,
dynamite, nitroglycerine, and ammonium nitrate/fuel oil
(ANFO) mixtures. It is custom to rank the explosive
destructive capability in terns of TNT equivalents, for
example, plastic bonded explosives such as Semtex may
contain 1.5 times the explosive destructive power as TNT
on an unit weight basis.
Low order explosives create a
subsonic explosion. Burn rates may be on the order of
inches to yards per second. The characteristic
overpressurization shock wave is not produced. Examples
are gunpowder, pipe bombs, ignition of gasoline vapors,
Molotov cocktails, and aircraft used as guided missiles.
A vapor cloud explosion that occurs if the chemical
concentration in the air is between the lower and upper
explosion limits and is ignited fall into this
Injury patterns are different for
high order as opposed to low order explosives.
Terrorists will use whatever is
available, high order explosives or low order explosives
or a combination thereof. They may be military issued or
purchased from a supplier or
Propellants are explosives used in
the propulsion of projectiles in firearms and rockets.
The propellant may be a low explosive such as
gelatinized nitrocellulose, but it may also be a mixture
of a low explosive and a high explosive such as
nitroglycerine. The propellant must deliver enough force
to deliver the projectile from a gun but not generate a
sudden shock that might break the gun. Some propellants
used are as follows:
Smokeless powder: An explosive used
as a propellant which may be gelatinized nitrocellulose
or nitrocellulose mixed with nitroglycerine. The name is
a misnomer because it is neither free from smoke when
exploded nor is it a true powder. Double-based smokeless
powder or explosive refers to the combination
nitrocellulose mixed with nitroglycerine.
Cordite: A double based, explosive
contains 30 to 40% nitroglycerine, nitrocellulose, and a
small quantity of petroleum jelly as a
High Explosives and Detonators
Many of the high explosives including
TNT, RDX, PETN, and plastic bonded explosives such as
C-4 and Semtex have a high resistance to shock or
friction and can be safely stored and handled. Other
high explosives such as nitroglycerin are so sensitive
to detonation that they are almost always mixed with an
inert desensitizer. Sometimes the high explosives are
mixed to form various compositions. Examples of
Composition B: A mixture of TNT and
wax; used in bombs.
Torpex: A mixture of TNT, wax, and
aluminum. Especially effective for underwater charges.
Pentolite: A mixture of TNT and PETN
Cyclotol: A mixture of RDX and TNT.
Cyclonite is another name for RDX.
Detonators are compounds which are
used to detonate the relatively insensitive high
explosives. The detonators will explode under conditions
of relative mild shock or heat, and this explosion is
enough to set off the main charge. Examples of
- Mercury fulminate
- Mercury fulminate and potassium
- Lead azide
- Lead styphnate
- Mannitol hexanitrate
A blasting cap or exploder is a small
charge of a detonator designed to be embedded with the
main explosive (e.g. dynamite) and ignited by a burning
fuse or a spark.
The following information was
obtained from the Center for Disease Control website at
Explosions produce unique patterns of
personnel injury. The injuries associated with the blast
may be subdivided into four categories as in table 1,
Blast Injuries may include:
1: Mechanisms of Blast Injury
to high explosives, results from the impact of the
over-pressurization wave with body
filled structures are most susceptible - lungs, GI
tract, and middle ear.
lung (pulmonary barotrauma) Tympanic
membrane (TM ) rupture and middle ear
hemorrhage and perforation - Globe (eye) rupture-
Concussion (Traumatic brain injury without
physical signs of head injury)
from flying debris and bomb fragments.
body part may be affected.
ballistic (fragmentation) or blunt injuries
penetration (can be occult)
from individuals being thrown by the blast
body part may be affected.
and traumatic amputation Closed
and open brain injury
explosion-related injuries, illnesses, or diseases
not due to primary, secondary, or tertiary
exacerbation or complications of existing
body part may be affected.
(flash, partial, and full thickness) Crush
and open brain injury Asthma,
Chronic obstructive pulmonary disease, or other
breathing problems from dust, smoke, or toxic
What about Semtex and Terrorists?
lung” is a direct consequence of the high explosive
(HE) over-pressurization wave. It is the most common
fatal primary blast injury among initial survivors.
Signs of blast lung are usually present at the time of
initial evaluation, but they have been reported as
late as 48 hours after the explosion. Blast lung is
characterized by the clinical triad of apnea,
bradycardia, and hypotension. Pulmonary injuries vary
from scattered petechae to confluent hemorrhages.
Blast lung should be suspected for anyone with
dyspnea, cough, hemoptysis, or chest pain following
blast exposure. Blast lung produces a characteristic
“butterfly” pattern on chest X-ray. A chest X-ray is
recommended for all exposed persons and a prophylactic
chest tube (thoracostomy) is recommended before
general anesthesia or air transport is indicated if
blast lung is suspected.
blast injuries of the auditory system cause
significant morbidity, but are easily overlooked.
Injury is dependent on the orientation of the ear to
the blast. TM perforation is the most common injury to
the middle ear. Signs of ear injury are usually
present at time of initial evaluation and should be
suspected for anyone presenting with hearing loss,
tinnitus, otalgia, vertigo, bleeding from the external
canal, TM rupture, or mucopurulent otorhea. All
patients exposed to blast should have an otologic
assessment and audiometry.
sections of the GI tract are most vulnerable to
primary blast effect. This can cause immediate bowel
perforation, hemorrhage (ranging from small petechiae
to large hematomas), mesenteric shear injuries, solid
organ lacerations, and testicular rupture. Blast
abdominal injury should be suspected in anyone exposed
to an explosion with abdominal pain, nausea, vomiting,
hematemesis, rectal pain, tenesmus, testicular pain,
unexplained hypovolemia, or any findings suggestive of
an acute abdomen. Clinical findings may be absent
until the onset of complications;
- Brain Injury: Primary blast
waves can cause concussions or mild traumatic brain
injury (MTBI) without a direct blow to the head.
Consider the proximity of the victim to the blast
particularly when given complaints of headache,
fatigue, poor concentration, lethargy, depression,
anxiety, insomnia, or other constitutional symptoms.
As mentioned before, Semtex is a
trade name for plastic bonded explosive manufactured by
Explosia near Prague in the Czech Republic. An article
which appeared in the magazine, Chemical Week,
Jan 30, 2002, stated that the Czech government will
acquire Explosia from its owner Unipetrol during 2002.
An article in the Sunday Mirror (an English newspaper)
stated that about 7000 metric tons of Semtex was
exported to Libya, Iraq, and North Korea during the
1970’s and 1980’s, at least some of which was delivered
to terrorists [see http://www.intellnet.org/news/2002/11/16/13551-1.html
]. Even after the Czech government took control of
Explosia there were reports of Semtex seizures [ see http://www.buzzle.com/editorials/text7-9-2002-22092.asp
]. There are reports of stolen Semtex [
http://www.rense.com/general20/sem.htm ]. Semtex is a
favorite choice of terrorists [ see http://www.kreten.8m.com/new/semtex.htm
]. It is believed that
world stockpiles of Semtex may be 40,000 tons. Only 12
ounces of Semtex molded inside a Toshiba cassette
recorder brought down Pan Am flight 103 near Locherbie,
Scotland, in 1988, killing 270 people. [see Christian
Science monitor article, http://www.csmonitor.com/2002/0226/p07s02-woeu.html
for additional details]. Semtex was
invented in 1966 by Stanislav Brebera as an explosive
for industrial use and also to safely clear land mines.
It was named after the town of Semtin in Czechoslovakia
where Brebera invented it. Shortly after its invention,
Czechoslovakia began supplying the explosive to North
Detection of Semtex
Approximately 40 varieties of
Semtex has been produced by Explosia. It comes in a
variety of colors, including red, yellow, black, white,
or grey-brown. It is a putty-like material can be molded
into almost any shape. For example, Semtex 1A, used for
blasting operations, is in the form of red bricks.
Semtex 10SE, used primarily for hardening metals, is in
the form of white sheets. Semtex has a lifetime of 20+
years. It is essentially odorless and can pass through
undetected through airport detectors. More recently, a “smelly”
version of Semtex has been invented which can be
detected by sniffer dogs. Metal traces have also been
added to the explosive which enable the material to be
detected by airport scanners. This formulation will also
deteriorate after 3 years making it harder for
terrorists to stockpile the material. The U.S. military explosive
C-4 is also invisible to airport x-rays and is
essentially odorless, but it is Semtex that has fallen
into the wrong hands. Both C-4 and Semtex contain the
explosives RDX and PETN; however, Sentex is reported to
be an improvement over C-4, using a styrene-butadiene
rubber binder to give much-improved consistency and
Detection of explosives depend upon
the fact that explosives leak minute amounts of vapor to
the air. There are several devices available as well as
use of trained sniffer dogs for detection of these
vapors. Sniffer dogs are probably the most effective
option available today. The problem is that these
methods are usually not sensitive enough, especially in
the case of Semtex where the explosives are well
A fairly technical article on
explosive detection published by the Dept. of Energy can
be obtained from the Internet at http://www.osti.gov/bridge/product.biblio.jsp?osti_id=666025.
The magazine, Nature, 23
October 2002, [see http://www.nature.com/nsu/021021/021021-3.html
], carried an article on a British team who developed a
methodology for on-spot detection of minute traces of
RDX vapor with the sensitivity of a few trillionths of a
gram. The sensor device uses a sodium amalgam in
mercury, which converts the RDX to a compound which is
detected by surface-enhanced Raman scattering.
More information on commercially
available explosive detection equipment can be obtained
by visiting the following websites:
Scintrex Trace Corp.
Control Screening LLC
Implant Science Corp.
Advanced Canine Technologies (sniffer
Medimpex United Inc (aerosol field
For a guide and listing of explosive
detection systems visit the website